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 the compilers cc(1) and pc(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      check and reset stream status
       fclose        close a stream
       fdopen        stream open functions
       feof          check and reset stream status
       ferror        check and reset stream status
       fflush        flush a stream
       fgetc         get next character or word from input stream
       fgetpos       reposition a stream
       fgets         get a line from a stream
       fileno        return the integer descriptor of the argument stream
       fopen         stream open functions
       fprintf       formatted output conversion
       fpurge        flush a stream
       fputc         output a character or word to a stream
       fputs         output a line to a stream
       fread         binary stream input/output
       freopen       stream open functions
       fscanf        input format conversion
       fseek         reposition a stream
       fsetpos       reposition a stream
       ftell         reposition a stream
       fwrite        binary stream input/output
       getc          get next character or word from input stream
       getchar       get next character or word from input stream
       gets          get a line from a stream
       getw          get next character or word from input stream
       mktemp        make temporary filename (unique)
       perror        system error messages
       printf        formatted output conversion
       putc          output a character or word to a stream
       putchar       output a character or word to a stream
       puts          output a line to a stream
       putw          output a character or word to a stream
       remove        remove directory entry
       rewind        reposition a stream
       scanf         input format conversion
       setbuf        stream buffering operations
       setbuffer     stream buffering operations
       setlinebuf    stream buffering operations
       setvbuf       stream buffering operations
       sprintf       formatted output conversion
       sscanf        input format conversion
       strerror      system error messages
       sys_errlist   system error messages
       sys_nerr      system error messages
       tempnam       temporary file routines
       tmpfile       temporary file routines

       tmpnam        temporary file routines
       ungetc        un-get character from input stream
       vfprintf      formatted output conversion
       vfscanf       input format conversion
       vprintf       formatted output conversion
       vscanf        input format conversion
       vsprintf      formatted output conversion
       vsscanf       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 4.13 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

                                 2001-12-26                         STDIO(3)

Pages that refer to this page: pmsnap(1)_exit(2)fcntl(2)vfork(2)curs_addch(3x)exit(3)ferror(3)popen(3)stdin(3)unlocked_stdio(3)