C Pocket Reference

Conversion Between Strings and Numbers

A variety of functions are declared in the header file stdlib.h to obtain numerical interpretations of the initial digit characters in a string. The resulting number is the return value of the function.

int atoi( const char *s );

Interprets the contents of the string s as a number with type int. The analogous functions atol(), atoll() ^(*), and atof() are used to convert a string into a number with type long, long long ^(*), or double.

double strtod( const char *s, char **pptr );

Serves a similar purpose to that of atof(), but takes the address of a char pointer as a second argument. If the char pointer referenced by pptr is not NULL, it is set to the first character in the string s (excluding any leading whitespace) that is not part of the substring representing a floating-point number.

The corresponding functions for conversion to the types float and long double are strtof() ^(*) and strtold() ^(*).

long strtol( const char *s, char **pptr, int base );

Converts a string to a number with type long. The third parameter is the base of the numeral string, and may be an integer between 2 and 36, or 0. If base is 0, the string s is interpreted as a numeral in base 8, 16, or 10, depending on whether it begins with 0, 0x, or one of the digits 1 to 9.

The analogous functions for converting a string to unsigned long, long long ^(*) or unsigned long long ^(*) are strtoul() ^(*), strtoll() ^(*), and strtoull() ^(*).

The header file inttypes.h