1 | =head1 NAME
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2 |
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3 | perlapio - perl's IO abstraction interface.
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4 |
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5 | =head1 SYNOPSIS
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6 |
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7 | #define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */
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8 | #include <perlio.h> /* Usually via #include <perl.h> */
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9 |
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10 | PerlIO *PerlIO_stdin(void);
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11 | PerlIO *PerlIO_stdout(void);
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12 | PerlIO *PerlIO_stderr(void);
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13 |
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14 | PerlIO *PerlIO_open(const char *path,const char *mode);
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15 | PerlIO *PerlIO_fdopen(int fd, const char *mode);
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16 | PerlIO *PerlIO_reopen(const char *path, const char *mode, PerlIO *old); /* deprecated */
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17 | int PerlIO_close(PerlIO *f);
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18 |
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19 | int PerlIO_stdoutf(const char *fmt,...)
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20 | int PerlIO_puts(PerlIO *f,const char *string);
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21 | int PerlIO_putc(PerlIO *f,int ch);
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22 | int PerlIO_write(PerlIO *f,const void *buf,size_t numbytes);
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23 | int PerlIO_printf(PerlIO *f, const char *fmt,...);
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24 | int PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args);
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25 | int PerlIO_flush(PerlIO *f);
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26 |
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27 | int PerlIO_eof(PerlIO *f);
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28 | int PerlIO_error(PerlIO *f);
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29 | void PerlIO_clearerr(PerlIO *f);
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30 |
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31 | int PerlIO_getc(PerlIO *d);
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32 | int PerlIO_ungetc(PerlIO *f,int ch);
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33 | int PerlIO_read(PerlIO *f, void *buf, size_t numbytes);
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34 |
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35 | int PerlIO_fileno(PerlIO *f);
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36 |
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37 | void PerlIO_setlinebuf(PerlIO *f);
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38 |
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39 | Off_t PerlIO_tell(PerlIO *f);
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40 | int PerlIO_seek(PerlIO *f, Off_t offset, int whence);
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41 | void PerlIO_rewind(PerlIO *f);
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42 |
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43 | int PerlIO_getpos(PerlIO *f, SV *save); /* prototype changed */
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44 | int PerlIO_setpos(PerlIO *f, SV *saved); /* prototype changed */
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45 |
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46 | int PerlIO_fast_gets(PerlIO *f);
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47 | int PerlIO_has_cntptr(PerlIO *f);
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48 | int PerlIO_get_cnt(PerlIO *f);
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49 | char *PerlIO_get_ptr(PerlIO *f);
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50 | void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, int count);
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51 |
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52 | int PerlIO_canset_cnt(PerlIO *f); /* deprecated */
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53 | void PerlIO_set_cnt(PerlIO *f, int count); /* deprecated */
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54 |
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55 | int PerlIO_has_base(PerlIO *f);
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56 | char *PerlIO_get_base(PerlIO *f);
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57 | int PerlIO_get_bufsiz(PerlIO *f);
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58 |
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59 | PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
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60 | FILE *PerlIO_exportFILE(PerlIO *f, int flags);
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61 | FILE *PerlIO_findFILE(PerlIO *f);
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62 | void PerlIO_releaseFILE(PerlIO *f,FILE *stdio);
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63 |
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64 | int PerlIO_apply_layers(PerlIO *f, const char *mode, const char *layers);
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65 | int PerlIO_binmode(PerlIO *f, int ptype, int imode, const char *layers);
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66 | void PerlIO_debug(const char *fmt,...)
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67 |
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68 | =head1 DESCRIPTION
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69 |
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70 | Perl's source code, and extensions that want maximum portability,
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71 | should use the above functions instead of those defined in ANSI C's
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72 | I<stdio.h>. The perl headers (in particular "perlio.h") will
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73 | C<#define> them to the I/O mechanism selected at Configure time.
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74 |
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75 | The functions are modeled on those in I<stdio.h>, but parameter order
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76 | has been "tidied up a little".
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77 |
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78 | C<PerlIO *> takes the place of FILE *. Like FILE * it should be
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79 | treated as opaque (it is probably safe to assume it is a pointer to
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80 | something).
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81 |
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82 | There are currently three implementations:
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83 |
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84 | =over 4
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85 |
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86 | =item 1. USE_STDIO
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87 |
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88 | All above are #define'd to stdio functions or are trivial wrapper
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89 | functions which call stdio. In this case I<only> PerlIO * is a FILE *.
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90 | This has been the default implementation since the abstraction was
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91 | introduced in perl5.003_02.
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92 |
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93 | =item 2. USE_SFIO
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94 |
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95 | A "legacy" implementation in terms of the "sfio" library. Used for
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96 | some specialist applications on Unix machines ("sfio" is not widely
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97 | ported away from Unix). Most of above are #define'd to the sfio
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98 | functions. PerlIO * is in this case Sfio_t *.
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99 |
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100 | =item 3. USE_PERLIO
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101 |
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102 | Introduced just after perl5.7.0, this is a re-implementation of the
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103 | above abstraction which allows perl more control over how IO is done
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104 | as it decouples IO from the way the operating system and C library
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105 | choose to do things. For USE_PERLIO PerlIO * has an extra layer of
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106 | indirection - it is a pointer-to-a-pointer. This allows the PerlIO *
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107 | to remain with a known value while swapping the implementation around
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108 | underneath I<at run time>. In this case all the above are true (but
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109 | very simple) functions which call the underlying implementation.
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110 |
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111 | This is the only implementation for which C<PerlIO_apply_layers()>
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112 | does anything "interesting".
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113 |
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114 | The USE_PERLIO implementation is described in L<perliol>.
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115 |
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116 | =back
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117 |
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118 | Because "perlio.h" is a thin layer (for efficiency) the semantics of
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119 | these functions are somewhat dependent on the underlying implementation.
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120 | Where these variations are understood they are noted below.
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121 |
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122 | Unless otherwise noted, functions return 0 on success, or a negative
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123 | value (usually C<EOF> which is usually -1) and set C<errno> on error.
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124 |
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125 | =over 4
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126 |
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127 | =item B<PerlIO_stdin()>, B<PerlIO_stdout()>, B<PerlIO_stderr()>
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128 |
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129 | Use these rather than C<stdin>, C<stdout>, C<stderr>. They are written
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130 | to look like "function calls" rather than variables because this makes
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131 | it easier to I<make them> function calls if platform cannot export data
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132 | to loaded modules, or if (say) different "threads" might have different
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133 | values.
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134 |
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135 | =item B<PerlIO_open(path, mode)>, B<PerlIO_fdopen(fd,mode)>
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136 |
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137 | These correspond to fopen()/fdopen() and the arguments are the same.
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138 | Return C<NULL> and set C<errno> if there is an error. There may be an
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139 | implementation limit on the number of open handles, which may be lower
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140 | than the limit on the number of open files - C<errno> may not be set
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141 | when C<NULL> is returned if this limit is exceeded.
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142 |
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143 | =item B<PerlIO_reopen(path,mode,f)>
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144 |
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145 | While this currently exists in all three implementations perl itself
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146 | does not use it. I<As perl does not use it, it is not well tested.>
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147 |
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148 | Perl prefers to C<dup> the new low-level descriptor to the descriptor
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149 | used by the existing PerlIO. This may become the behaviour of this
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150 | function in the future.
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151 |
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152 | =item B<PerlIO_printf(f,fmt,...)>, B<PerlIO_vprintf(f,fmt,a)>
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153 |
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154 | These are fprintf()/vfprintf() equivalents.
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155 |
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156 | =item B<PerlIO_stdoutf(fmt,...)>
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157 |
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158 | This is printf() equivalent. printf is #defined to this function,
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159 | so it is (currently) legal to use C<printf(fmt,...)> in perl sources.
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160 |
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161 | =item B<PerlIO_read(f,buf,count)>, B<PerlIO_write(f,buf,count)>
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162 |
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163 | These correspond functionally to fread() and fwrite() but the
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164 | arguments and return values are different. The PerlIO_read() and
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165 | PerlIO_write() signatures have been modeled on the more sane low level
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166 | read() and write() functions instead: The "file" argument is passed
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167 | first, there is only one "count", and the return value can distinguish
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168 | between error and C<EOF>.
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169 |
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170 | Returns a byte count if successful (which may be zero or
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171 | positive), returns negative value and sets C<errno> on error.
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172 | Depending on implementation C<errno> may be C<EINTR> if operation was
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173 | interrupted by a signal.
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174 |
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175 | =item B<PerlIO_close(f)>
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176 |
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177 | Depending on implementation C<errno> may be C<EINTR> if operation was
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178 | interrupted by a signal.
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179 |
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180 | =item B<PerlIO_puts(f,s)>, B<PerlIO_putc(f,c)>
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181 |
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182 | These correspond to fputs() and fputc().
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183 | Note that arguments have been revised to have "file" first.
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184 |
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185 | =item B<PerlIO_ungetc(f,c)>
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186 |
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187 | This corresponds to ungetc(). Note that arguments have been revised
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188 | to have "file" first. Arranges that next read operation will return
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189 | the byte B<c>. Despite the implied "character" in the name only
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190 | values in the range 0..0xFF are defined. Returns the byte B<c> on
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191 | success or -1 (C<EOF>) on error. The number of bytes that can be
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192 | "pushed back" may vary, only 1 character is certain, and then only if
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193 | it is the last character that was read from the handle.
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194 |
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195 | =item B<PerlIO_getc(f)>
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196 |
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197 | This corresponds to getc().
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198 | Despite the c in the name only byte range 0..0xFF is supported.
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199 | Returns the character read or -1 (C<EOF>) on error.
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200 |
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201 | =item B<PerlIO_eof(f)>
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202 |
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203 | This corresponds to feof(). Returns a true/false indication of
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204 | whether the handle is at end of file. For terminal devices this may
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205 | or may not be "sticky" depending on the implementation. The flag is
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206 | cleared by PerlIO_seek(), or PerlIO_rewind().
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207 |
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208 | =item B<PerlIO_error(f)>
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209 |
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210 | This corresponds to ferror(). Returns a true/false indication of
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211 | whether there has been an IO error on the handle.
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212 |
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213 | =item B<PerlIO_fileno(f)>
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214 |
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215 | This corresponds to fileno(), note that on some platforms, the meaning
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216 | of "fileno" may not match Unix. Returns -1 if the handle has no open
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217 | descriptor associated with it.
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218 |
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219 | =item B<PerlIO_clearerr(f)>
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220 |
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221 | This corresponds to clearerr(), i.e., clears 'error' and (usually)
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222 | 'eof' flags for the "stream". Does not return a value.
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223 |
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224 | =item B<PerlIO_flush(f)>
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225 |
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226 | This corresponds to fflush(). Sends any buffered write data to the
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227 | underlying file. If called with C<NULL> this may flush all open
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228 | streams (or core dump with some USE_STDIO implementations). Calling
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229 | on a handle open for read only, or on which last operation was a read
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230 | of some kind may lead to undefined behaviour on some USE_STDIO
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231 | implementations. The USE_PERLIO (layers) implementation tries to
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232 | behave better: it flushes all open streams when passed C<NULL>, and
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233 | attempts to retain data on read streams either in the buffer or by
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234 | seeking the handle to the current logical position.
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235 |
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236 | =item B<PerlIO_seek(f,offset,whence)>
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237 |
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238 | This corresponds to fseek(). Sends buffered write data to the
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239 | underlying file, or discards any buffered read data, then positions
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240 | the file descriptor as specified by B<offset> and B<whence> (sic).
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241 | This is the correct thing to do when switching between read and write
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242 | on the same handle (see issues with PerlIO_flush() above). Offset is
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243 | of type C<Off_t> which is a perl Configure value which may not be same
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244 | as stdio's C<off_t>.
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245 |
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246 | =item B<PerlIO_tell(f)>
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247 |
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248 | This corresponds to ftell(). Returns the current file position, or
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249 | (Off_t) -1 on error. May just return value system "knows" without
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250 | making a system call or checking the underlying file descriptor (so
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251 | use on shared file descriptors is not safe without a
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252 | PerlIO_seek()). Return value is of type C<Off_t> which is a perl
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253 | Configure value which may not be same as stdio's C<off_t>.
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254 |
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255 | =item B<PerlIO_getpos(f,p)>, B<PerlIO_setpos(f,p)>
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256 |
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257 | These correspond (loosely) to fgetpos() and fsetpos(). Rather than
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258 | stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What is
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259 | stored there should be considered opaque. The layout of the data may
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260 | vary from handle to handle. When not using stdio or if platform does
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261 | not have the stdio calls then they are implemented in terms of
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262 | PerlIO_tell() and PerlIO_seek().
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263 |
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264 | =item B<PerlIO_rewind(f)>
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265 |
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266 | This corresponds to rewind(). It is usually defined as being
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267 |
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268 | PerlIO_seek(f,(Off_t)0L, SEEK_SET);
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269 | PerlIO_clearerr(f);
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270 |
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271 | =item B<PerlIO_tmpfile()>
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272 |
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273 | This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
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274 | NULL on error. The system will attempt to automatically delete the
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275 | file when closed. On Unix the file is usually C<unlink>-ed just after
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276 | it is created so it does not matter how it gets closed. On other
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277 | systems the file may only be deleted if closed via PerlIO_close()
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278 | and/or the program exits via C<exit>. Depending on the implementation
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279 | there may be "race conditions" which allow other processes access to
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280 | the file, though in general it will be safer in this regard than
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281 | ad. hoc. schemes.
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282 |
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283 | =item B<PerlIO_setlinebuf(f)>
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284 |
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285 | This corresponds to setlinebuf(). Does not return a value. What
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286 | constitutes a "line" is implementation dependent but usually means
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287 | that writing "\n" flushes the buffer. What happens with things like
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288 | "this\nthat" is uncertain. (Perl core uses it I<only> when "dumping";
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289 | it has nothing to do with $| auto-flush.)
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290 |
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291 | =back
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292 |
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293 | =head2 Co-existence with stdio
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294 |
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295 | There is outline support for co-existence of PerlIO with stdio.
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296 | Obviously if PerlIO is implemented in terms of stdio there is no
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297 | problem. However in other cases then mechanisms must exist to create a
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298 | FILE * which can be passed to library code which is going to use stdio
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299 | calls.
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300 |
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301 | The first step is to add this line:
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302 |
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303 | #define PERLIO_NOT_STDIO 0
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304 |
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305 | I<before> including any perl header files. (This will probably become
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306 | the default at some point). That prevents "perlio.h" from attempting
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307 | to #define stdio functions onto PerlIO functions.
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308 |
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309 | XS code is probably better using "typemap" if it expects FILE *
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310 | arguments. The standard typemap will be adjusted to comprehend any
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311 | changes in this area.
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312 |
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313 | =over 4
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314 |
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315 | =item B<PerlIO_importFILE(f,mode)>
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316 |
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317 | Used to get a PerlIO * from a FILE *.
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318 |
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319 | The mode argument should be a string as would be passed to
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320 | fopen/PerlIO_open. If it is NULL then - for legacy support - the code
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321 | will (depending upon the platform and the implementation) either
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322 | attempt to empirically determine the mode in which I<f> is open, or
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323 | use "r+" to indicate a read/write stream.
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324 |
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325 | Once called the FILE * should I<ONLY> be closed by calling
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326 | C<PerlIO_close()> on the returned PerlIO *.
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327 |
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328 | The PerlIO is set to textmode. Use PerlIO_binmode if this is
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329 | not the desired mode.
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330 |
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331 | This is B<not> the reverse of PerlIO_exportFILE().
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332 |
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333 | =item B<PerlIO_exportFILE(f,mode)>
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334 |
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335 | Given a PerlIO * create a 'native' FILE * suitable for passing to code
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336 | expecting to be compiled and linked with ANSI C I<stdio.h>. The mode
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337 | argument should be a string as would be passed to fopen/PerlIO_open.
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338 | If it is NULL then - for legacy support - the FILE * is opened in same
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339 | mode as the PerlIO *.
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340 |
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341 | The fact that such a FILE * has been 'exported' is recorded, (normally
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342 | by pushing a new :stdio "layer" onto the PerlIO *), which may affect
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343 | future PerlIO operations on the original PerlIO *. You should not
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344 | call C<fclose()> on the file unless you call C<PerlIO_releaseFILE()>
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345 | to disassociate it from the PerlIO *. (Do not use PerlIO_importFILE()
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346 | for doing the disassociation.)
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347 |
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348 | Calling this function repeatedly will create a FILE * on each call
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349 | (and will push an :stdio layer each time as well).
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350 |
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351 | =item B<PerlIO_releaseFILE(p,f)>
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352 |
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353 | Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
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354 | complete. It is removed from the list of 'exported' FILE *s, and the
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355 | associated PerlIO * should revert to its original behaviour.
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356 |
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357 | Use this to disassociate a file from a PerlIO * that was associated
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358 | using PerlIO_exportFILE().
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359 |
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360 | =item B<PerlIO_findFILE(f)>
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361 |
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362 | Returns a native FILE * used by a stdio layer. If there is none, it
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363 | will create one with PerlIO_exportFILE. In either case the FILE *
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364 | should be considered as belonging to PerlIO subsystem and should
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365 | only be closed by calling C<PerlIO_close()>.
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366 |
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367 |
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368 | =back
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369 |
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370 | =head2 "Fast gets" Functions
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371 |
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372 | In addition to standard-like API defined so far above there is an
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373 | "implementation" interface which allows perl to get at internals of
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374 | PerlIO. The following calls correspond to the various FILE_xxx macros
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375 | determined by Configure - or their equivalent in other
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376 | implementations. This section is really of interest to only those
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377 | concerned with detailed perl-core behaviour, implementing a PerlIO
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378 | mapping or writing code which can make use of the "read ahead" that
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379 | has been done by the IO system in the same way perl does. Note that
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380 | any code that uses these interfaces must be prepared to do things the
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381 | traditional way if a handle does not support them.
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382 |
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383 | =over 4
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384 |
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385 | =item B<PerlIO_fast_gets(f)>
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386 |
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387 | Returns true if implementation has all the interfaces required to
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388 | allow perl's C<sv_gets> to "bypass" normal IO mechanism. This can
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389 | vary from handle to handle.
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390 |
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391 | PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
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392 | PerlIO_canset_cnt(f) && \
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393 | `Can set pointer into buffer'
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394 |
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395 |
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396 | =item B<PerlIO_has_cntptr(f)>
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397 |
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398 | Implementation can return pointer to current position in the "buffer"
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399 | and a count of bytes available in the buffer. Do not use this - use
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400 | PerlIO_fast_gets.
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401 |
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402 | =item B<PerlIO_get_cnt(f)>
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403 |
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404 | Return count of readable bytes in the buffer. Zero or negative return
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405 | means no more bytes available.
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406 |
|
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407 | =item B<PerlIO_get_ptr(f)>
|
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408 |
|
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409 | Return pointer to next readable byte in buffer, accessing via the
|
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410 | pointer (dereferencing) is only safe if PerlIO_get_cnt() has returned
|
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411 | a positive value. Only positive offsets up to value returned by
|
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412 | PerlIO_get_cnt() are allowed.
|
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413 |
|
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414 | =item B<PerlIO_set_ptrcnt(f,p,c)>
|
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415 |
|
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416 | Set pointer into buffer, and a count of bytes still in the
|
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417 | buffer. Should be used only to set pointer to within range implied by
|
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418 | previous calls to C<PerlIO_get_ptr> and C<PerlIO_get_cnt>. The two
|
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419 | values I<must> be consistent with each other (implementation may only
|
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420 | use one or the other or may require both).
|
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421 |
|
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422 | =item B<PerlIO_canset_cnt(f)>
|
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423 |
|
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424 | Implementation can adjust its idea of number of bytes in the buffer.
|
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425 | Do not use this - use PerlIO_fast_gets.
|
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426 |
|
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427 | =item B<PerlIO_set_cnt(f,c)>
|
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428 |
|
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429 | Obscure - set count of bytes in the buffer. Deprecated. Only usable
|
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430 | if PerlIO_canset_cnt() returns true. Currently used in only doio.c to
|
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431 | force count less than -1 to -1. Perhaps should be PerlIO_set_empty or
|
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432 | similar. This call may actually do nothing if "count" is deduced from
|
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433 | pointer and a "limit". Do not use this - use PerlIO_set_ptrcnt().
|
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434 |
|
---|
435 | =item B<PerlIO_has_base(f)>
|
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436 |
|
---|
437 | Returns true if implementation has a buffer, and can return pointer
|
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438 | to whole buffer and its size. Used by perl for B<-T> / B<-B> tests.
|
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439 | Other uses would be very obscure...
|
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440 |
|
---|
441 | =item B<PerlIO_get_base(f)>
|
---|
442 |
|
---|
443 | Return I<start> of buffer. Access only positive offsets in the buffer
|
---|
444 | up to the value returned by PerlIO_get_bufsiz().
|
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445 |
|
---|
446 | =item B<PerlIO_get_bufsiz(f)>
|
---|
447 |
|
---|
448 | Return the I<total number of bytes> in the buffer, this is neither the
|
---|
449 | number that can be read, nor the amount of memory allocated to the
|
---|
450 | buffer. Rather it is what the operating system and/or implementation
|
---|
451 | happened to C<read()> (or whatever) last time IO was requested.
|
---|
452 |
|
---|
453 | =back
|
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454 |
|
---|
455 | =head2 Other Functions
|
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456 |
|
---|
457 | =over 4
|
---|
458 |
|
---|
459 | =item PerlIO_apply_layers(f,mode,layers)
|
---|
460 |
|
---|
461 | The new interface to the USE_PERLIO implementation. The layers ":crlf"
|
---|
462 | and ":raw" are only ones allowed for other implementations and those
|
---|
463 | are silently ignored. (As of perl5.8 ":raw" is deprecated.) Use
|
---|
464 | PerlIO_binmode() below for the portable case.
|
---|
465 |
|
---|
466 | =item PerlIO_binmode(f,ptype,imode,layers)
|
---|
467 |
|
---|
468 | The hook used by perl's C<binmode> operator.
|
---|
469 | B<ptype> is perl's character for the kind of IO:
|
---|
470 |
|
---|
471 | =over 8
|
---|
472 |
|
---|
473 | =item 'E<lt>' read
|
---|
474 |
|
---|
475 | =item 'E<gt>' write
|
---|
476 |
|
---|
477 | =item '+' read/write
|
---|
478 |
|
---|
479 | =back
|
---|
480 |
|
---|
481 | B<imode> is C<O_BINARY> or C<O_TEXT>.
|
---|
482 |
|
---|
483 | B<layers> is a string of layers to apply, only ":crlf" makes sense in
|
---|
484 | the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in favour
|
---|
485 | of passing NULL.)
|
---|
486 |
|
---|
487 | Portable cases are:
|
---|
488 |
|
---|
489 | PerlIO_binmode(f,ptype,O_BINARY,Nullch);
|
---|
490 | and
|
---|
491 | PerlIO_binmode(f,ptype,O_TEXT,":crlf");
|
---|
492 |
|
---|
493 | On Unix these calls probably have no effect whatsoever. Elsewhere
|
---|
494 | they alter "\n" to CR,LF translation and possibly cause a special text
|
---|
495 | "end of file" indicator to be written or honoured on read. The effect
|
---|
496 | of making the call after doing any IO to the handle depends on the
|
---|
497 | implementation. (It may be ignored, affect any data which is already
|
---|
498 | buffered as well, or only apply to subsequent data.)
|
---|
499 |
|
---|
500 | =item PerlIO_debug(fmt,...)
|
---|
501 |
|
---|
502 | PerlIO_debug is a printf()-like function which can be used for
|
---|
503 | debugging. No return value. Its main use is inside PerlIO where using
|
---|
504 | real printf, warn() etc. would recursively call PerlIO and be a
|
---|
505 | problem.
|
---|
506 |
|
---|
507 | PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} typical
|
---|
508 | use might be
|
---|
509 |
|
---|
510 | Bourne shells (sh, ksh, bash, zsh, ash, ...):
|
---|
511 | PERLIO_DEBUG=/dev/tty ./perl somescript some args
|
---|
512 |
|
---|
513 | Csh/Tcsh:
|
---|
514 | setenv PERLIO_DEBUG /dev/tty
|
---|
515 | ./perl somescript some args
|
---|
516 |
|
---|
517 | If you have the "env" utility:
|
---|
518 | env PERLIO_DEBUG=/dev/tty ./perl somescript some args
|
---|
519 |
|
---|
520 | Win32:
|
---|
521 | set PERLIO_DEBUG=CON
|
---|
522 | perl somescript some args
|
---|
523 |
|
---|
524 | If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a no-op.
|
---|
525 |
|
---|
526 | =back
|
---|