usr/share/man/cat3/fopen.0



FOPEN(3)                      1989                       FOPEN(3)


N\bNA\bAM\bME\bE
     fopen, freopen, fdopen - open a stream

S\bSY\bYN\bNO\bOP\bPS\bSI\bIS\bS
     #\b#i\bin\bnc\bcl\blu\bud\bde\be <\b<s\bst\btd\bdi\bio\bo.\b.h\bh>\b>

     F\bFI\bIL\bLE\bE *\b*f\bfo\bop\bpe\ben\bn(\b(f\bfi\bil\ble\ben\bna\bam\bme\be,\b, t\bty\byp\bpe\be)\b)
     c\bch\bha\bar\br *\b*f\bfi\bil\ble\ben\bna\bam\bme\be,\b, *\b*t\bty\byp\bpe\be;\b;

     F\bFI\bIL\bLE\bE *\b*f\bfr\bre\beo\bop\bpe\ben\bn(\b(f\bfi\bil\ble\ben\bna\bam\bme\be,\b, t\bty\byp\bpe\be,\b, s\bst\btr\bre\bea\bam\bm)\b)
     c\bch\bha\bar\br *\b*f\bfi\bil\ble\ben\bna\bam\bme\be,\b, *\b*t\bty\byp\bpe\be;\b;
     F\bFI\bIL\bLE\bE *\b*s\bst\btr\bre\bea\bam\bm;\b;

     F\bFI\bIL\bLE\bE *\b*f\bfd\bdo\bop\bpe\ben\bn(\b(f\bfi\bil\bld\bde\bes\bs,\b, t\bty\byp\bpe\be)\b)
     c\bch\bha\bar\br *\b*t\bty\byp\bpe\be;\b;

D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
     _\bF_\bo_\bp_\be_\bn opens the file named by _\bf_\bi_\bl_\be_\bn_\ba_\bm_\be and associates a
     stream with it.  _\bF_\bo_\bp_\be_\bn returns a pointer to be used to iden-
     tify the stream in subsequent operations.

     _\bT_\by_\bp_\be is a character string having one of the following
     values:

     "r"  open for reading

     "w"  create for writing

     "a"  append: open for writing at end of file, or create for
          writing

     In addition, each _\bt_\by_\bp_\be may be followed by a "+" to have the
     file opened for reading and writing.  "r+" positions the
     stream at the beginning of the file, "w+" creates or trun-
     cates it, and "a+" positions it at the end.  Both reads and
     writes may be used on read/write streams, with the limita-
     tion that an _\bf_\bs_\be_\be_\bk, _\br_\be_\bw_\bi_\bn_\bd, or reading an end-of-file must
     be used between a read and a write or vice-versa.

     _\bF_\br_\be_\bo_\bp_\be_\bn substitutes the named file in place of the open
     _\bs_\bt_\br_\be_\ba_\bm.  It returns the original value of _\bs_\bt_\br_\be_\ba_\bm.  The ori-
     ginal stream is closed.

     _\bF_\br_\be_\bo_\bp_\be_\bn is typically used to attach the preopened constant
     names, s\bst\btd\bdi\bin\bn,\b, s\bst\btd\bdo\bou\but\bt,\b, s\bst\btd\bde\ber\brr\br,\b, to specified files.

     _\bF_\bd_\bo_\bp_\be_\bn associates a stream with a file descriptor obtained
     from _\bo_\bp_\be_\bn, _\bd_\bu_\bp, _\bc_\br_\be_\ba_\bt, or _\bp_\bi_\bp_\be(2).  The _\bt_\by_\bp_\be of the stream
     must agree with the mode of the open file.

S\bSE\bEE\bE A\bAL\bLS\bSO\bO
     open(2), fclose(3)


Printed 7/27/90               April                             1


FOPEN(3)                      1989                       FOPEN(3)


D\bDI\bIA\bAG\bGN\bNO\bOS\bST\bTI\bIC\bCS\bS
     _\bF_\bo_\bp_\be_\bn and _\bf_\br_\be_\bo_\bp_\be_\bn return the pointer N\bNU\bUL\bLL\bL if _\bf_\bi_\bl_\be_\bn_\ba_\bm_\be cannot
     be accessed, if too many files are already open, or if other
     resources needed cannot be allocated.

B\bBU\bUG\bGS\bS
     _\bF_\bd_\bo_\bp_\be_\bn is not portable to systems other than UNIX.

     The read/write _\bt_\by_\bp_\be_\bs do not exist on all systems.        Those
     systems without read/write modes will probably treat the
     _\bt_\by_\bp_\be as if the "+" was not present.  These are unreliable in
     any event.

     In order to support the same number of open files as does
     the system, _\bf_\bo_\bp_\be_\bn must allocate additional memory for data
     structures using _\bc_\ba_\bl_\bl_\bo_\bc after 20 files have been opened.
     This confuses some programs which use their own memory allo-
     cators.  An undocumented routine, _\bf__\bp_\br_\be_\ba_\bl_\bl_\bo_\bc, may be called
     to force immediate allocation of all internal memory except
     for buffers.


Printed 7/27/90               April                             2