atoi, atol, atoll

Header: <stdlib.h>

Interprets an integer value in a byte string pointed to by str. The implied radix is always 10.

# Declarations

int atoi ( const char* str );

long atol ( const char* str );

long long atoll( const char* str );

(since C99)

# Parameters

# Return value

Integer value corresponding to the contents of str on success.

# Notes

The name stands for “ASCII to integer”.

# Example

#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    printf("%i\n", atoi(" -123junk"));
    printf("%i\n", atoi(" +321dust"));
    printf("%i\n", atoi("0"));
    printf("%i\n", atoi("0042")); // treated as a decimal number with leading zeros
    printf("%i\n", atoi("0x2A")); // only leading zero is converted discarding "x2A"
    printf("%i\n", atoi("junk")); // no conversion can be performed
    printf("%i\n", atoi("2147483648")); // UB: out of range of int
}

# See also