stdio

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



NAME
       stdio - standard input/output library functions

SYNOPSIS
       #include <stdio.h>

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

DESCRIPTION
       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 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 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
       The stdio library conforms to C89.

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

COLOPHON
       This page is part of release 5.13 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
       https://www.kernel.org/doc/man-pages/.



                                   2021-03-22                           STDIO(3)