stdio(3) — Linux manual page


STDIO(3)                  Linux Programmer's Manual                 STDIO(3)

NAME         top

       stdio - standard input/output library functions

SYNOPSIS         top

       #include <stdio.h>

       FILE *stdin;
       FILE *stdout;
       FILE *stderr;

DESCRIPTION         top

       The standard I/O library provides a simple and efficient buffered
       stream I/O interface.  Input and output is mapped into logical data
       streams and the physical I/O characteristics are concealed.  The
       functions and macros are listed below; more information is available
       from the individual man pages.

       A stream is associated with an external file (which may be a physical
       device) by opening a file, which may involve creating a new file.
       Creating an existing file causes its former contents to be discarded.
       If a file can support positioning requests (such as a disk file, as
       opposed to a terminal), then a file position indicator associated
       with the stream is positioned at the start of the file (byte zero),
       unless the file is opened with append mode.  If append mode is used,
       it is unspecified whether the position indicator will be placed at
       the start or the end of the file.  The position indicator is
       maintained by subsequent reads, writes and positioning requests.  All
       input occurs as if the characters were read by successive calls to
       the fgetc(3) function; all output takes place as if all characters
       were written by successive calls to the fputc(3) function.

       A file is disassociated from a stream by closing the file.  Output
       streams are flushed (any unwritten buffer contents are transferred to
       the host environment) before the stream is disassociated from the
       file.  The value of a pointer to a FILE object is indeterminate after
       a file is closed (garbage).

       A file may be subsequently reopened, by the same or another program
       execution, and its contents reclaimed or modified (if it can be
       repositioned at the start).  If the main function returns to its
       original caller, or the exit(3) function is called, all open files
       are closed (hence all output streams are flushed) before program
       termination.  Other methods of program termination, such as abort(3)
       do not bother about closing files properly.

       At program startup, three text streams are predefined and need not be
       opened explicitly: standard input (for reading conventional input),
       standard output (for writing conventional output), and standard error
       (for writing diagnostic output).  These streams are abbreviated
       stdin, stdout, and stderr.  When opened, the standard error stream is
       not fully buffered; the standard input and output streams are fully
       buffered if and only if the streams do not refer to an interactive

       Output streams that refer to terminal devices are always line
       buffered by default; pending output to such streams is written
       automatically whenever an input stream that refers to a terminal
       device is read.  In cases where a large amount of computation is done
       after printing part of a line on an output terminal, it is necessary
       to fflush(3) the standard output before going off and computing so
       that the output will appear.

       The stdio library is a part of the library libc and routines are
       automatically loaded as needed by cc(1).  The SYNOPSIS sections of
       the following manual pages indicate which include files are to be
       used, what the compiler declaration for the function looks like and
       which external variables are of interest.

       The following are defined as macros; these names may not be reused
       without first removing their current definitions with #undef: BUFSIZ,
       EOF, FILENAME_MAX, FOPEN_MAX, L_cuserid, L_ctermid, L_tmpnam, NULL,
       SEEK_END, SEEK_SET, SEEK_CUR, TMP_MAX, clearerr, feof, ferror,
       fileno, getc, getchar, putc, putchar, stderr, stdin, stdout.
       Function versions of the macro functions feof, ferror, clearerr,
       fileno, getc, getchar, putc, and putchar exist and will be used if
       the macros definitions are explicitly removed.

   List of functions
       Function         Description
       clearerr(3)      check and reset stream status
       fclose(3)        close a stream
       fdopen(3)        stream open functions
       feof(3)          check and reset stream status
       ferror(3)        check and reset stream status
       fflush(3)        flush a stream
       fgetc(3)         get next character or word from input stream
       fgetpos(3)       reposition a stream
       fgets(3)         get a line from a stream
       fileno(3)        return the integer descriptor of the argument stream
       fopen(3)         stream open functions
       fprintf(3)       formatted output conversion
       fpurge(3)        flush a stream
       fputc(3)         output a character or word to a stream
       fputs(3)         output a line to a stream
       fread(3)         binary stream input/output
       freopen(3)       stream open functions
       fscanf(3)        input format conversion
       fseek(3)         reposition a stream
       fsetpos(3)       reposition a stream
       ftell(3)         reposition a stream
       fwrite(3)        binary stream input/output
       getc(3)          get next character or word from input stream
       getchar(3)       get next character or word from input stream
       gets(3)          get a line from a stream
       getw(3)          get next character or word from input stream
       mktemp(3)        make temporary filename (unique)
       perror(3)        system error messages
       printf(3)        formatted output conversion
       putc(3)          output a character or word to a stream
       putchar(3)       output a character or word to a stream
       puts(3)          output a line to a stream
       putw(3)          output a character or word to a stream
       remove(3)        remove directory entry
       rewind(3)        reposition a stream
       scanf(3)         input format conversion
       setbuf(3)        stream buffering operations
       setbuffer(3)     stream buffering operations
       setlinebuf(3)    stream buffering operations
       setvbuf(3)       stream buffering operations
       sprintf(3)       formatted output conversion
       sscanf(3)        input format conversion
       strerror(3)      system error messages
       sys_errlist(3)   system error messages
       sys_nerr(3)      system error messages
       tempnam(3)       temporary file routines
       tmpfile(3)       temporary file routines

       tmpnam(3)        temporary file routines
       ungetc(3)        un-get character from input stream
       vfprintf(3)      formatted output conversion
       vfscanf(3)       input format conversion
       vprintf(3)       formatted output conversion
       vscanf(3)        input format conversion
       vsprintf(3)      formatted output conversion
       vsscanf(3)       input format conversion

CONFORMING TO         top

       The stdio library conforms to C89.

SEE ALSO         top

       close(2), open(2), read(2), write(2), stdout(3), unlocked_stdio(3)

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

                                 2017-11-26                         STDIO(3)

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