strtoul, strtoull

< c‎ | string‎ | byte

Defined in header <stdlib.h>
unsigned long      strtoul( const char          *str, char          **str_end,
                            int base );
(until C99)
unsigned long      strtoul( const char *restrict str, char **restrict str_end,
                            int base );
(since C99)
unsigned long long strtoull( const char *restrict str, char **restrict str_end,
                             int base );
(since C99)

Interprets an unsigned integer value in a byte string pointed to by str.

Function discards any whitespace characters (as identified by calling isspace()) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid base-n (where n=base) unsigned integer number representation and converts them to an integer value. The valid unsigned integer value consists of the following parts:

  • (optional) prefix (0) indicating octal base (applies only when the base is 8 or 0)
  • (optional) prefix (0x or 0X) indicating hexadecimal base (applies only when the base is 16 or 0)
  • a sequence of digits

The set of valid digits for base-2 integer is 01, for base-3 integer is 012, and so on. For bases larger than 10, valid digits include alphabetic characters, starting from Aa for base-11 integer, to Zz for base-36 integer. The case of the characters is ignored.

Additional numeric formats may be accepted by the currently installed C locale.

If the value of base is 0, the numeric base is auto-detected: if the prefix is 0, the base is octal, if the prefix is 0x or 0X, the base is hexadecimal, otherwise the base is decimal.

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is NULL, it is ignored.


[edit] Parameters

str - pointer to the null-terminated byte string to be interpreted
str_end - pointer to a pointer to character.
base - base of the interpreted integer value

[edit] Return value

Integer value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs and ULONG_MAX or ULLONG_MAX is returned. If no conversion can be performed, 0 is returned.

[edit] Example

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
int main(void) 
    /* Decimal */
    printf("%lu\n", strtoul("",NULL,10));        /* empty string           */
    printf("%lu\n", strtoul(" +0123",NULL,10));  /* leading space and zero */
    printf("%lu\n", strtoul("123",NULL,0));
    /* Binary */
    printf("%lu\n", strtoul("1100", NULL,2));
    /* Octal */
    printf("%lu\n", strtoul("14",NULL,8));
    printf("%lu\n", strtoul("014",NULL,0));
    /* Base 13 */
    printf("%lu\n", strtoul("1c",NULL,13));
    /* Hexadecimal */
    printf("%lu\n", strtoul("FFFFFFFFFFFFFFFF",NULL,16));
    printf("%lu\n", strtoul("0xFFFFFFFFFFFFFFFF",NULL,0));
    /* Base 36 */
    printf("%lu\n", strtoul("XyZ",NULL,36));   /* 44027 */
    /* Overflow, a value too large for type unsigned long int. */
    errno = 0;
    printf("%lu\n", strtoul("18446744073709551616",NULL,10));           
    printf("%s\n",strerror(errno));   /* range error */
    /* Underflow. a value too small for type unsigned long int. */
    errno = 0;
    printf("%lu\n", strtoul("-1",NULL,10));
    printf("%s\n",strerror(errno));   /* success */
    /* Using str_end. */
    char *str_end;
    printf("%lu\n", strtoul("  00123 999",&str_end,10));
    printf("[%c]\n", *str_end);
    printf("%lu\n", strtoul(str_end,NULL,10)); 
    return 0;


Numerical result out of range
[ ]

[edit] See also

converts a byte string to an integer value
converts a byte string to an integer value
C++ documentation for strtoul