ATOI(3) Linux Programmer's Manual ATOI(3)
NAME
atoi, atol, atoll - convert a string to an integer
SYNOPSIS
#include <stdlib.h>
int atoi(const char *nptr);
long atol(const char *nptr);
long long atoll(const char *nptr);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
atoll():
_ISOC99_SOURCE ||
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
The atoi() function converts the initial portion of the string pointed
to by nptr to int. The behavior is the same as
strtol(nptr, NULL, 10);
except that atoi() does not detect errors.
The atol() and atoll() functions behave the same as atoi(), except that
they convert the initial portion of the string to their return type of
long or long long.
RETURN VALUE
The converted value or 0 on error.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├────────────────────────┼───────────────┼────────────────┤
│atoi(), atol(), atoll() │ Thread safety │ MT-Safe locale │
└────────────────────────┴───────────────┴────────────────┘
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99, SVr4, 4.3BSD. C89 and POSIX.1-1996
include the functions atoi() and atol() only.
NOTES
POSIX.1 leaves the return value of atoi() on error unspecified. On
glibc, musl libc, and uClibc, 0 is returned on error.
BUGS
errno is not set on error so there is no way to distinguish between 0
as an error and as the converted value. No checks for overflow or un-
derflow are done. Only base-10 input can be converted. It is recom-
mended to instead use the strtol() and strtoul() family of functions in
new programs.
SEE ALSO
atof(3), strtod(3), strtol(3), strtoul(3)
COLOPHON
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latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
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