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ComputingCStdlib.h

strtol

Convert a string value to a long, long long, intmax_t or quad_t integer
+ View other versions (3)

Interface

#include <stdlib.h> ;
#include <limits.h>
long strtol (const char * restrict nptr, char ** restrict endptr, int base)
long strtoll (const char * restrict nptr, char ** restrict endptr, int base)

#include <inttypes.h>
intmax_t strtoimax (const char * restrict nptr, char ** restrict endptr, int base)

#include <sys/types.h> ; #include <stdlib.h> ; #include <limits.h>
quad_t strtoq (const char *nptr, char **endptr, int base)

Description

The strtol function converts the string in \c nptr to a long value. The strtoll function converts the string in \c nptr to a long long value. The strtoimax function converts the string in \c nptr to an intmax_t value. The strtoq function converts the string in \c nptr to a quad_t value. The conversion is done according to the given \c base, which must be between 2 and 36 inclusive, or be the special value 0.

The string may begin with an arbitrary amount of white space (as determined by isspace) followed by a single optional + or - sign. If \c base is zero or 16, the string may then include a 0x prefix, and the number will be read in base 16; otherwise, a zero \c base is taken as 10 (decimal) unless the next character is 0, in which case it is taken as 8 (octal).

The remainder of the string is converted to a long, long long, intmax_t or quad_t value in the obvious manner, stopping at the first character which is not a valid digit in the given base. (In bases above 10, the letter A in either upper or lower case represents 10, B represents 11, and so forth, with Z representing 35.)

If \c endptr is not NULL, strtol stores the address of the first invalid character in \c *endptr. If there were no digits at all, however, strtol stores the original value of \c nptr in \c *endptr. (Thus, if \c *nptr is not \0 but \c **endptr is \0 on return, the entire string was valid.)

Extended locale versions of these functions are documented in strtol_l. See xlocale for more information.

The code below shows how to use the strtol function to convert a number from base 2 to base 10.

Example:

Example - Convert a string value to a long, long long, intmax_t or quad_t integer
Workings
#include <stdio.h>
#include <stdlib.h>
int main ()
{
  char binary[10] = "101010101", *end;
  long x = strtol(binary, &end, 2);
  printf("%s in base 2 = %ld in base 10\n", binary, x);
  return 0;
}
Solution

Output:
101010101 in base 2 = 341 in base 10

Return Values

The strtol, strtoll, strtoimax and strtoq functions return the result of the conversion, unless the value would underflow or overflow. If no conversion could be performed, 0 is returned and the global variable errno is set to EINVAL. If an overflow or underflow occurs, errno is set to ERANGE and the function return value is clamped according to the following table.
Function overflow underflow
strtol LONG_MIN LONG_MAX
strtoll LLONG_MIN LLONG_MAX
strtoimax INTMAX_MIN INTMAX_MAX
strtoq LLONG_MIN LLONG_MAX

Errors

EINVAL The value of \c base is not supported or no conversion could be performed.
ERANGE The given string was out of range; the value converted has been clamped.

Standards

The strtol function conforms to ISO/IEC 9899:1990 ("ISO C90"). The strtoll and strtoimax functions conform to ISO/IEC 9899:1999 ("ISO C99"). The BSD strtoq function is deprecated.