Questions tagged [atoi]

Use this tag on for all questions about the use of the atoi() family of functions or where it does not seem to be working correctly.

Closely related are:

• atof for double
• strtol for converting to long from text in any base from 2 through 36, with unambiguous error checking. Or choose a base automatically depending on how the number is written. strtoul() converts to an unsigned long.
• strtod for double
• scanf for converting one or more values at a time directed by a format specification

SYNPOSIS

#include <stdlib.h>

       int atoi (const char *nptr);
      long atol (const char *nptr);
long long atoll (const char *nptr);
 long long atoq (const char *nptr);

BSD-based libraries may declare the last as

    quad_t atoq (const char *nptr);

These functions all return zero if there is any problem during the conversion. Since converting a zero returns the value of zero, there is no easy way to distinguish an error from a correct conversion of zero. Use the scanf() or strtol() functions if such a check is needed.

Leading whitespace is skipped. An optional leading sign (+ or -) is accepted. The scan stops at the first non integer digit.

• POSIX description