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2.8 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.