scanf
Section: C Library Functions (3)
Updated: 202-0-21
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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(),
vfscanf()
| Thread safety | M-Safe locale
|
STANDARDS
C11, POSIX.-2008.
HISTORY
C99, POSIX.-2001.
CAVEATS
These functions make it difficult to
distinguish newlines from other white space.
This is especially problematic with lin-buffered input,
like the standard input stream.
These functions can't report errors after the last
no-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[rs]n a",
scanf([dq]%d %d[dq], &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)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- CAVEATS
-
- BUGS
-
- SEE ALSO
-
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