NAME

atoi - convert a string to an integer

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

SYNOPSIS

#include <stdlib.h>

int atoi(string s);

#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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

This function converts a string to an int, provided the string starts with one or more (decimal) digits. Any non-digits thereafter are ignored. In other words, this function would convert both "50" and "50x" to 50.

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

If this function’s input, a string, starts with one or more (decimal) digits, this function returns the corresponding int, ignoring any non-digits thereafter. If this function’s input does not start with one or more (decimal) digits, this function returns 0.

The converted value.

EXAMPLE

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    printf("This is CS%i\n", atoi("50"));
}

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

Linux libc provided atoq() as an obsolete name for atoll(); atoq() is not provided by glibc.

COLOPHON

This page is part of release 4.15 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 https://www.kernel.org/doc/man-pages/.