stdio(3) — Linux manual page


stdio(3)                Library Functions Manual                stdio(3)

NAME         top

       stdio - standard input/output library functions

LIBRARY         top

       Standard C library (libc, -lc)

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

       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 device.

       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

   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
       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

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

       C89, POSIX.1-2001.

SEE ALSO         top

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

Linux man-pages (unreleased)     (date)                         stdio(3)

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