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Annotation of 43BSDReno/lib/libc/stdio/fopen.3, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)fopen.3     6.4 (Berkeley) 4/1/89
        !             6: .\"
        !             7: .TH FOPEN 3  "April 1, 1989"
        !             8: .UC 4
        !             9: .SH NAME
        !            10: fopen, freopen, fdopen \- open a stream
        !            11: .SH SYNOPSIS
        !            12: .B #include <stdio.h>
        !            13: .PP
        !            14: .SM
        !            15: .B FILE
        !            16: .B *fopen(filename, type)
        !            17: .br
        !            18: .B char *filename, *type;
        !            19: .PP
        !            20: .SM
        !            21: .B FILE
        !            22: .B *freopen(filename, type, stream)
        !            23: .br
        !            24: .B char *filename, *type;
        !            25: .br
        !            26: .SM
        !            27: .B FILE
        !            28: .B *stream;
        !            29: .PP
        !            30: .SM
        !            31: .B FILE
        !            32: .B *fdopen(fildes, type)
        !            33: .br
        !            34: .B char *type;
        !            35: .SH DESCRIPTION
        !            36: .I Fopen
        !            37: opens the file named by
        !            38: .I filename
        !            39: and associates a stream with it.
        !            40: .I Fopen
        !            41: returns a pointer to be used to identify the stream in subsequent operations.
        !            42: .PP
        !            43: .I Type
        !            44: is a character string having one of the following values:
        !            45: .TP 5
        !            46: "r"
        !            47: open for reading
        !            48: .ns
        !            49: .TP 5
        !            50: "w"
        !            51: create for writing
        !            52: .ns
        !            53: .TP 5
        !            54: "a"
        !            55: append: open for writing at end of file, or create for writing
        !            56: .PP
        !            57: In addition, each
        !            58: .I type
        !            59: may be followed by a "+" to have the file opened for reading and writing.
        !            60: "r+" positions the stream at the beginning of the file, "w+" creates
        !            61: or truncates it, and "a+" positions it at the end.  Both reads and writes
        !            62: may be used on read/write streams, with the limitation that an
        !            63: .I fseek, rewind,
        !            64: or reading an end-of-file must be used between a read and a write or vice-versa.
        !            65: .PP
        !            66: .I Freopen
        !            67: substitutes the named file in place of the open
        !            68: .IR stream .
        !            69: It returns the original value of
        !            70: .IR stream .
        !            71: The original stream is closed.
        !            72: .PP
        !            73: .I Freopen
        !            74: is typically used to attach the preopened constant names,
        !            75: .B stdin, stdout, stderr,
        !            76: to specified files.
        !            77: .PP
        !            78: .I Fdopen
        !            79: associates a stream with a file descriptor obtained from
        !            80: .I open, dup, creat,
        !            81: or
        !            82: .IR pipe (2).
        !            83: The
        !            84: .I type
        !            85: of the stream must agree with the mode of the open file.
        !            86: .SH "SEE ALSO"
        !            87: open(2),
        !            88: fclose(3)
        !            89: .SH DIAGNOSTICS
        !            90: .I Fopen
        !            91: and 
        !            92: .I freopen
        !            93: return the pointer
        !            94: .SM
        !            95: .B NULL
        !            96: if
        !            97: .I filename
        !            98: cannot be accessed,
        !            99: if too many files are already open,
        !           100: or if other resources needed cannot be allocated.
        !           101: .SH BUGS
        !           102: .I Fdopen
        !           103: is not portable to systems other than UNIX.
        !           104: .PP
        !           105: The read/write 
        !           106: .I types
        !           107: do not exist on all systems.  Those systems without
        !           108: read/write modes will probably treat the 
        !           109: .I type
        !           110: as if the "+" was not present.  These are unreliable in any event.
        !           111: .PP
        !           112: In order to support the same number of open files as does the system,
        !           113: .I fopen
        !           114: must allocate additional memory for data structures using
        !           115: .I calloc
        !           116: after 20 files have been opened.
        !           117: This confuses some programs which use their own memory allocators.
        !           118: An undocumented routine,
        !           119: .IR f_prealloc ,
        !           120: may be called to force immediate allocation of all internal memory
        !           121: except for buffers.

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