scanf(3)                   Library Functions Manual                   scanf(3)

NAME
       scanf, fscanf, vscanf, vfscanf - input FILE format conversion

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <stdio.h>

       int scanf(const char *restrict format, ...);
       int fscanf(FILE *restrict stream,
                  const char *restrict format, ...);

       #include <stdarg.h>

       int vscanf(const char *restrict format, va_list ap);
       int vfscanf(FILE *restrict stream,
                  const char *restrict format, va_list ap);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       vscanf(), vfscanf():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       The scanf() family of functions scans formatted input like sscanf(3),
       but read from a FILE.  It is very difficult to use these functions
       correctly, and it is preferable to read entire lines with fgets(3) or
       getline(3) and parse them later with sscanf(3) or more specialized
       functions such as strtol(3).

       The scanf() function reads input from the standard input stream stdin
       and fscanf() reads input from the stream pointer stream.

       The vfscanf() function is analogous to vfprintf(3) and reads input from
       the stream pointer stream using a variable argument list of pointers
       (see stdarg(3).  The vscanf() function is analogous to vprintf(3) and
       reads from the standard input.

RETURN VALUE
       On success, these functions return the number of input items
       successfully matched and assigned; this can be fewer than provided for,
       or even zero, in the event of an early matching failure.

       The value EOF is returned if the end of input is reached before either
       the first successful conversion or a matching failure occurs.  EOF is
       also returned if a read error occurs, in which case the error indicator
       for the stream (see ferror(3)) is set, and errno is set to indicate the
       error.

ERRORS
       EAGAIN The file descriptor underlying stream is marked nonblocking, and
              the read operation would block.

       EBADF  The file descriptor underlying stream is invalid, or not open
              for reading.

       EILSEQ Input byte sequence does not form a valid character.

       EINTR  The read operation was interrupted by a signal; see signal(7).

       EINVAL Not enough arguments; or format is NULL.

       ENOMEM Out of memory.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +-------------------------------------+---------------+----------------+
       |Interface                            | Attribute     | Value          |
       +-------------------------------------+---------------+----------------+
       |scanf (), fscanf (), vscanf (),      | Thread safety | MT-Safe locale |
       |vfscanf ()                           |               |                |
       +-------------------------------------+---------------+----------------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       C99, POSIX.1-2001.

CAVEATS
       These functions make it difficult to distinguish newlines from other
       white space, This is especially problematic with line-buffered input,
       like the standard input stream.

       These functions can't report errors after the last non-suppressed
       conversion specification.

BUGS
       It is impossible to accurately know how many characters these functions
       have consumed from the input stream, since they only report the number
       of successful conversions.  For example, if the input is "123\n a",
       scanf("%d %d", &a, &b) will consume the digits, the newline, and the
       space, but not the letter a.  This makes it difficult to recover from
       invalid input.

SEE ALSO
       fgets(3), getline(3), sscanf(3)

Linux man-pages 6.7               2023-12-09                          scanf(3)