Manpages - atoi.3

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

  #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).

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

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

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)

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