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# strtol, strtoll

From cppreference.com
< c‎ | string‎ | byte

Defined in header `<stdlib.h>` |  |

long strtol( const char *str, char **str_end, int base ); |  | (until C99)
long strtol( const char *restrict str, char **restrict str_end, int base ); |  | (since C99)
long long strtoll( const char *restrict str, char **restrict str_end, int base ); |  | (since C99)

Interprets an 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) integer number representation and converts them to an integer value. The valid integer value consists of the following parts:

- (optional) plus or minus sign
- (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. In non-default locales, additional numeric formats may be accepted.

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.

If the `str` is empty or does not have the expected form, no conversion is performed, and (if `str_end` is not NULL) the value of `str` is stored in the object pointed to by `str_end`.

### [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

- If successful, an integer value corresponding to the contents of `str` is returned.
- If the converted value falls out of range of corresponding return type, a range error occurs (setting errno to ERANGE) and LONG_MAX, LONG_MIN, LLONG_MAX or LLONG_MIN is returned.
- If no conversion can be performed, ​0​ is returned.

### [edit] Example

Run this code

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <errno.h>

    int main()
    {
        char str[] = "Is 0xff bigger than 0 or 0x00? The answer is 42.";
        int i = 0;
        int len = strlen(str);
        char *num;

        while (i < len) {
            long found = strtol(&str[i], &num, 0);

            if (errno) {
                perror("Error");
                exit(EXIT_FAILURE);
            } else if (found || num != &str[i]) {
                printf("Found %li at position %d\n", found, i);
                i = num - str;
            } else {
                i++;
            }
        }

        /* Base 36 */
        printf("\n%ld\n", strtol("XyZ",NULL,36));

        /* Overflow (range error) */
        errno = 0;
        printf("%ld\n", strtol("9223372036854775808",NULL,10));   // LONG_MAX+1 --> LONG_MAX
        printf("errno = %d\n", errno);                            // 34, range error

        return 0;
    }

Output:

    Found 255 at position 2
    Found 0 at position 19
    Found 0 at position 24
    Found 42 at position 44

    44027
    9223372036854775807
    errno = 34

### [edit] See also

atoi atol atoll | converts a byte string to an integer value (function) [edit]
strtoul strtoull | converts a byte string to an unsigned integer value (function) [edit]
C++ documentation for strtol, strtoll

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