1STDIO(3) Linux Programmer's Manual STDIO(3)
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6 stdio - standard input/output library functions
7
9 #include <stdio.h>
10 FILE *stdin;
12 FILE *stdout;
13 FILE *stderr;
14
16 The standard I/O library provides a simple and efficient buffered
17 stream I/O interface. Input and output is mapped into logical data
18 streams and the physical I/O characteristics are concealed. The func‐
19 tions and macros are listed below; more information is available from
20 the individual man pages.
21 A stream is associated with an external file (which may be a physical
23 device) by opening a file, which may involve creating a new file. Cre‐
24 ating an existing file causes its former contents to be discarded. If
25 a file can support positioning requests (such as a disk file, as op‐
26 posed to a terminal), then a file position indicator associated with
27 the stream is positioned at the start of the file (byte zero), unless
28 the file is opened with append mode. If append mode is used, it is un‐
29 specified whether the position indicator will be placed at the start or
30 the end of the file. The position indicator is maintained by subse‐
31 quent reads, writes, and positioning requests. All input occurs as if
32 the characters were read by successive calls to the fgetc(3) function;
33 all output takes place as if all characters were written by successive
34 calls to the fputc(3) function.
35 A file is disassociated from a stream by closing the file. Output
37 streams are flushed (any unwritten buffer contents are transferred to
38 the host environment) before the stream is disassociated from the file.
39 The value of a pointer to a FILE object is indeterminate after a file
40 is closed (garbage).
41 A file may be subsequently reopened, by the same or another program ex‐
43 ecution, and its contents reclaimed or modified (if it can be reposi‐
44 tioned at the start). If the main function returns to its original
45 caller, or the exit(3) function is called, all open files are closed
46 (hence all output streams are flushed) before program termination.
47 Other methods of program termination, such as abort(3) do not bother
48 about closing files properly.
49 At program startup, three text streams are predefined and need not be
51 opened explicitly: standard input (for reading conventional input),
52 standard output (for writing conventional output), and standard error
53 (for writing diagnostic output). These streams are abbreviated stdin,
54 stdout, and stderr. When opened, the standard error stream is not
55 fully buffered; the standard input and output streams are fully
56 buffered if and only if the streams do not refer to an interactive de‐
57 vice.
58 Output streams that refer to terminal devices are always line buffered
60 by default; pending output to such streams is written automatically
61 whenever an input stream that refers to a terminal device is read. In
62 cases where a large amount of computation is done after printing part
63 of a line on an output terminal, it is necessary to fflush(3) the stan‐
64 dard output before going off and computing so that the output will ap‐
65 pear.
66 The stdio library is a part of the library libc and routines are auto‐
68 matically loaded as needed by cc(1). The SYNOPSIS sections of the fol‐
69 lowing manual pages indicate which include files are to be used, what
70 the compiler declaration for the function looks like and which external
71 variables are of interest.
72 The following are defined as macros; these names may not be reused
74 without first removing their current definitions with #undef: BUFSIZ,
75 EOF, FILENAME_MAX, FOPEN_MAX, L_cuserid, L_ctermid, L_tmpnam, NULL,
76 SEEK_END, SEEK_SET, SEEK_CUR, TMP_MAX, clearerr, feof, ferror, fileno,
77 getc, getchar, putc, putchar, stderr, stdin, stdout. Function versions
78 of the macro functions feof, ferror, clearerr, fileno, getc, getchar,
79 putc, and putchar exist and will be used if the macros definitions are
80 explicitly removed.
81 List of functions
83 Function Description
84 ────────────────────────────────────────────────────────────────────────
85 clearerr(3) check and reset stream status
86 fclose(3) close a stream
87 fdopen(3) stream open functions
88 feof(3) check and reset stream status
89 ferror(3) check and reset stream status
90 fflush(3) flush a stream
91 fgetc(3) get next character or word from input stream
92 fgetpos(3) reposition a stream
93 fgets(3) get a line from a stream
94 fileno(3) return the integer descriptor of the argument stream
95 fopen(3) stream open functions
96 fprintf(3) formatted output conversion
97 fpurge(3) flush a stream
98 fputc(3) output a character or word to a stream
99 fputs(3) output a line to a stream
100 fread(3) binary stream input/output
101 freopen(3) stream open functions
102 fscanf(3) input format conversion
103 fseek(3) reposition a stream
104 fsetpos(3) reposition a stream
105 ftell(3) reposition a stream
106 fwrite(3) binary stream input/output
107 getc(3) get next character or word from input stream
108 getchar(3) get next character or word from input stream
109 gets(3) get a line from a stream
110 getw(3) get next character or word from input stream
111 mktemp(3) make temporary filename (unique)
112 perror(3) system error messages
113 printf(3) formatted output conversion
114 putc(3) output a character or word to a stream
115 putchar(3) output a character or word to a stream
116 puts(3) output a line to a stream
117 putw(3) output a character or word to a stream
118 remove(3) remove directory entry
119 rewind(3) reposition a stream
120 scanf(3) input format conversion
121 setbuf(3) stream buffering operations
122 setbuffer(3) stream buffering operations
123 setlinebuf(3) stream buffering operations
124 setvbuf(3) stream buffering operations
125 sprintf(3) formatted output conversion
126 sscanf(3) input format conversion
127 strerror(3) system error messages
128 sys_errlist(3) system error messages
129 sys_nerr(3) system error messages
130 tempnam(3) temporary file routines
131 tmpfile(3) temporary file routines
132 tmpnam(3) temporary file routines
134 ungetc(3) un-get character from input stream
135 vfprintf(3) formatted output conversion
136 vfscanf(3) input format conversion
137 vprintf(3) formatted output conversion
138 vscanf(3) input format conversion
139 vsprintf(3) formatted output conversion
140 vsscanf(3) input format conversion
141
143 The stdio library conforms to C89.
144
146 close(2), open(2), read(2), write(2), stdout(3), unlocked_stdio(3)
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149 This page is part of release 5.13 of the Linux man-pages project. A
150 description of the project, information about reporting bugs, and the
151 latest version of this page, can be found at
152 https://www.kernel.org/doc/man-pages/.
153 2021-03-22 STDIO(3)