projects / unix-history / blame
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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 | .\" | |
| cf0272dc | 5 | .\" @(#)fopen.3 6.1 (Berkeley) %G% |
| 251f9c2d | 6 | .\" |
| cf0272dc | 7 | .TH FOPEN 3S "" |
| 251f9c2d KM |
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 | |
| e2703397 | 41 | returns a pointer to be used to identify the stream in subsequent operations. |
| 251f9c2d KM |
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" | |
| e2703397 | 55 | append: open for writing at end of file, or create for writing |
| 251f9c2d KM |
56 | .PP |
| 57 | In addition, each | |
| 58 | .I type | |
| e2703397 KM |
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 | |
| 251f9c2d KM |
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, | |
| e2703397 | 64 | or reading an end-of-file must be used between a read and a write or vice-versa. |
| 251f9c2d KM |
65 | .PP |
| 66 | .I Freopen | |
| e2703397 | 67 | substitutes the named file in place of the open |
| 251f9c2d KM |
68 | .IR stream . |
| 69 | It returns the original value of | |
| 70 | .IR stream . | |
| 71 | The original stream is closed. | |
| 72 | .PP | |
| 73 | .I Freopen | |
| e2703397 | 74 | is typically used to attach the preopened constant names, |
| 251f9c2d KM |
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 | .SH BUGS | |
| 100 | .I Fdopen | |
| 101 | is not portable to systems other than UNIX. | |
| 102 | .PP | |
| 103 | The read/write | |
| 104 | .I types | |
| 105 | do not exist on all systems. Those systems without | |
| 106 | read/write modes will probably treat the | |
| 107 | .I type | |
| e2703397 | 108 | as if the '+' was not present. These are unreliable in any event. |