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# std::strtoul, std::strtoull

From cppreference.com
< cpp‎ | string‎ | byte

Defined in header `<cstdlib>` |  |
unsigned long strtoul( const char *str, char **str_end, int base ); |  |
unsigned long long strtoull( const char *str, char **str_end, int base ); |  | (since C++11)

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

Run this code

    #include <iostream>
    #include <cstdlib>

    int main()
    {
        const char* begin = "10 200000000000000000000000000000 30 40";
        char *end;
        for (unsigned long i = std::strtoul(begin, &end, 10);
             begin != end;
             i = std::strtoul(begin, &end, 10))
        {
            begin = end;
            if (errno == ERANGE){
                std::cout << "range error\n";
                errno = 0;
            }
            std::cout << i << '\n';
        }
    }

Output:

    10
    range error
    18446744073709551615
    30
    40

### [edit] See also

atoiatolatoll | converts a byte string to an integer value (function) [edit]
strtolstrtoll | converts a byte string to an integer value (function) [edit]
C documentation for strtoul, strtoull

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