atoi, atol, atoll - cppreference.com (original) (raw)

Defined in header <stdlib.h>
int atoi ( const char* str );	(1)
long atol ( const char* str );	(2)
long long atoll( const char* str );	(3)	(since C99)

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

Discards any whitespace characters until the first non-whitespace character is found, then takes as many characters as possible to form a valid integer number representation and converts them to an integer value. The valid integer value consists of the following parts:

(optional) plus or minus sign
numeric digits

If the value of the result cannot be represented, i.e. the converted value falls out of range of the corresponding return type, the behavior is undefined.

[edit] Parameters

str	-	pointer to the null-terminated byte string to be interpreted

[edit] Return value

Integer value corresponding to the contents of str on success.

If no conversion can be performed, 0 is returned.

[edit] Notes

The name stands for “ASCII to integer”.

[edit] 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 }

Possible output:

-123 321 0 42 0 0 -2147483648

[edit] References