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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 posi‐
       tion 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)

                                                                               2021-03-22                                                                       STDIO(3)