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Manual Pages  — ATOI


atoi – convert ASCII string to integer



Standard C Library (libc, -lc)


#include <stdlib.h>

atoi(const char *nptr);


The atoi() function converts the initial portion of the string pointed to by nptr to int representation.

It is equivalent to:

(int)strtol(nptr, (char **)NULL, 10);

The atoi() function has been deprecated by strtol() and should not be used in new code.


The function atoi() need not affect the value of errno on an error.


atof(3), atol(3), strtod(3), strtol(3), strtoul(3)


The atoi() function conforms to IEEE Std 1003.1-90 ("POSIX.1"), ISO/IEC 9899:1990 ("ISO C90"), and ISO/IEC 9899:1999 ("ISO C99").

ATOI (3) June 4, 1993

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