atoi(3) — Linux manual page

atoi(3)                 Library Functions Manual                 atoi(3)

NAME

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

LIBRARY

       Standard C library (libc, -lc)

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 <= 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
       attributes(7).
       ┌──────────────────────────────┬───────────────┬────────────────┐
       │ Interface                    │ Attribute     │ Value          │
       ├──────────────────────────────┼───────────────┼────────────────┤
       │ atoi(), atol(), atoll()      │ Thread safety │ MT-Safe locale │
       └──────────────────────────────┴───────────────┴────────────────┘

VERSIONS

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

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       C99, POSIX.1-2001, SVr4, 4.3BSD.

       C89 and POSIX.1-1996 include the functions atoi() and atol()
       only.

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 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

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

COLOPHON

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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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