atoi(3) — Linux manual page


ATOI(3)                 Linux Programmer's Manual                ATOI(3)

NAME         top

       atoi, atol, atoll - convert a string to an integer

SYNOPSIS         top

       #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

               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION         top

       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         top

       The converted value or 0 on error.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                      Attribute     Value          │
       │atoi(), atol(), atoll()        │ Thread safety │ MT-Safe locale │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, C99, SVr4, 4.3BSD.  C89 and
       POSIX.1-1996 include the functions atoi() and atol() only.

NOTES         top

       POSIX.1 leaves the return value of atoi() on error unspecified.
       On glibc, musl libc, and uClibc, 0 is returned on error.

BUGS         top

       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.

SEE ALSO         top

       atof(3), strtod(3), strtol(3), strtoul(3)

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

GNU                            2021-03-22                        ATOI(3)

Pages that refer to this page: atof(3)form_field_validation(3x)strtod(3)strtol(3)strtoul(3)