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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 <= 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 │
       └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

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 underflow are done.  On‐
       ly 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)

GNU                                                                            2021-03-22                                                                        ATOI(3)