1STDIO(3) Linux Programmer's Manual STDIO(3)
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6 stdio - standard input/output library functions
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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
26 opposed 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
29 unspecified whether the position indicator will be placed at the start
30 or 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
43 execution, 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 input), and standard error
53 (for writing diagnostic output). These streams are abbreviated
54 stdin,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 to refer to an interactive
57 device.
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
65 appear.
66 The stdio library is a part of the library libc and routines are auto‐
68 matically loaded as needed by the compilers cc(1) and pc(1). The SYN‐
69 OPSIS sections of the following manual pages indicate which include
70 files are to be used, what the compiler declaration for the function
71 looks like and which external variables are of interest.
72 The following are defined as macros; these names may not be re-used
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, SEE_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
83 Function Description
84 clearerr check and reset stream status
86 fclose close a stream
88 fdopen stream open functions
90 feof check and reset stream status
92 ferror check and reset stream status
94 fflush flush a stream
96 fgetc get next character or word from input stream
98 fgetpos reposition a stream
100 fgets get a line from a stream
102 fileno return the integer descriptor of the argument stream
104 fopen stream open functions
106 fprintf formatted output conversion
108 fpurge flush a stream
110 fputc output a character or word to a stream
112 fputs output a line to a stream
114 fread binary stream input/output
116 freopen stream open functions
118 fscanf input format conversion
120 fseek reposition a stream
122 fsetpos reposition a stream
124 ftell reposition a stream
126 fwrite binary stream input/output
128 getc get next character or word from input stream
130 getchar get next character or word from input stream
132 gets get a line from a stream
134 getw get next character or word from input stream
136 mktemp make temporary filename (unique)
138 perror system error messages
140 printf formatted output conversion
142 putc output a character or word to a stream
144 putchar output a character or word to a stream
146 puts output a line to a stream
148 putw output a character or word to a stream
150 remove remove directory entry
152 rewind reposition a stream
154 scanf input format conversion
156 setbuf stream buffering operations
158 setbuffer stream buffering operations
160 setlinebuf
162 stream buffering operations
163 setvbuf stream buffering operations
165 sprintf formatted output conversion
167 sscanf input format conversion
169 strerror system error messages
171 sys_errlist
173 system error messages
174 sys_nerr system error messages
176 tempnam temporary file routines
178 tmpfile temporary file routines
180 tmpnam temporary file routines
182 ungetc un-get character from input stream
184 vfprintf formatted output conversion
186 vfscanf input format conversion
188 vprintf formatted output conversion
190 vscanf input format conversion
192 vsprintf formatted output conversion
194 vsscanf input format conversion
196
198 The stdio library conforms to C89.
199
201 close(2), open(2), read(2), write(2), stdout(3), unlocked_stdio(3)
202 2001-12-26 STDIO(3)