### 3.8 `atoi`, `atol`—string to integer ¶

Synopsis

    #include <stdlib.h>
    int atoi(const char *s);
    long atol(const char *s);
    int _atoi_r(struct _reent *ptr, const char *s);
    long _atol_r(struct _reent *ptr, const char *s);

Description
`atoi` converts the initial portion of a string to an `int`. `atol` converts the initial portion of a string to a `long`.

`atoi(s)` is implemented as `(int)strtol(s, NULL, 10).` `atol(s)` is implemented as `strtol(s, NULL, 10).`

`_atoi_r` and `_atol_r` are reentrant versions of `atoi` and `atol` respectively, passing the reentrancy struct pointer.

Returns
The functions return the converted value, if any. If no conversion was made, `0` is returned.

Portability
`atoi`, `atol` are ANSI.

No supporting OS subroutines are required.