atoi(3) Library Functions Manual atoi(3) atoi, atol, atoll - C (libc, -lc) #include int atoi(const char *nptr); long atol(const char *nptr); long long atoll(const char *nptr); glibc (. feature_test_macros(7)): atoll(): _ISOC99_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE atoi() , nptr, int. strtol(nptr, NULL, 10); atoi() . atol() atoll() , atoi(), , long long long. The converted value or 0 on error. attributes(7). +----------------------------+----------------------------------------------------------+--------------------------+ | | | | +----------------------------+----------------------------------------------------------+--------------------------+ |atoi(), atol(), atoll() | | 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) () Dmitry Bolkhovskikh Yuri Kozlov ; GNU (GNU General Public License - GPL, 3 ) , - . - , , () () () <>. Linux 6.9.1 2 2024 . atoi(3)