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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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atoi(3) Library Functions Manual atoi(3)
atoi, atol, atoll - convert a string to an integer
Standard C library (libc, -lc)
#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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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.
The converted value or 0 on error.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────┼───────────────┼────────────────┤
│ atoi(), atol(), atoll() │ Thread safety │ MT-Safe locale │
└──────────────────────────────┴───────────────┴────────────────┘
POSIX.1 leaves the return value of atoi() on error unspecified.
On glibc, musl libc, and uClibc, 0 is returned on error.
C11, POSIX.1-2008.
C99, POSIX.1-2001, SVr4, 4.3BSD.
C89 and POSIX.1-1996 include the functions atoi() and atol()
only.
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 underflow are done. Only base-10 input can be
converted. It is recommended to instead use the strtol() and
strtoul() family of functions in new programs.
atof(3), strtod(3), strtol(3), strtoul(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-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. 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
[email protected]
Linux man-pages 6.9.1 2024-05-02 atoi(3)
Pages that refer to this page: atof(3), form_field_validation(3x), strtod(3), strtol(3), strtoul(3)
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HTML rendering created 2024-06-26 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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