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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | CAVEATS | BUGS | SEE ALSO | COLOPHON |
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scanf(3) Library Functions Manual scanf(3)
scanf, fscanf, vscanf, vfscanf - input FILE format conversion
Standard C library (libc, -lc)
#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
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.
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.
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.
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() │ │ │
└───────────────────────────────┴───────────────┴────────────────┘
C11, POSIX.1-2008.
C99, POSIX.1-2001.
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.
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.
fgets(3), getline(3), sscanf(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 scanf(3)
Pages that refer to this page: curs_scanw(3x), fgetc(3), FILE(3type), getline(3), gets(3), intmax_t(3type), intN_t(3type), intptr_t(3type), lber-decode(3), pmfstring(3), printf(3), ptrdiff_t(3type), puts(3), size_t(3type), stdarg(3), stdio(3), strptime(3), void(3type), proc_pid_stat(5), locale(7), system_data_types(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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