Difference between revisions of "cpp/string/basic string/stol"

Revision as of 15:47, 24 February 2022

Interprets a signed integer value in the string str.

Discards any whitespace characters (as identified by calling std::isspace) until the first non-whitespace character is found, then 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 values for base is {0,2,3,...,36}. The set of valid digits for base-2 integers is {0,1}, for base-3 integers is {0,1,2}, 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.

If the minus sign was part of the input sequence, the numeric value calculated from the sequence of digits is negated as if by unary minus in the result type.

If pos is not a null pointer, then a pointer ptr - internal to the conversion functions - will receive the address of the first unconverted character in str.c_str(), and the index of that character will be calculated and stored in *pos, giving the number of characters that were processed by the conversion.

Parameters

Return value

Integer value corresponding to the content of str.

Exceptions

• std::invalid_argument if no conversion could be performed
• std::out_of_range if the converted value would fall out of the range of the result type or if the underlying function (std::strtol or std::strtoll) sets errno to ERANGE.

Example

#include <string>
#include <iomanip>
#include <iostream>
#include <stdexcept>
 
int main()
{
    const auto data = {
        "45",
        "+45",
        " -45",
        "3.14159",
        "31337 with words",
        "words and 2",
        "12345678901",
    };
 
    for (const std::string s : data)
    {
        std::size_t pos{};
        try
        {
            std::cout << "std::stoi('" << s << "'): ";
            const int i {std::stoi(s, &pos)};
            std::cout << i << "; pos: " << pos << '\n';
        }
        catch(std::invalid_argument const& ex)
        {
            std::cout << "... std::invalid_argument::what(): " << ex.what() << '\n';
        }
        catch(std::out_of_range const& ex)
        {
            std::cout << "... std::out_of_range::what(): " << ex.what() << '\n';
            const long long ll {std::stoll(s, &pos)};
            std::cout << "std::stoll('" << s << "'): " << ll << "; pos = " << pos << '\n';
        }
    }
 
    std::cout << "\nCalling with different radixes:\n";
    for (const int base: {2, 3, 4, 8, 10, 12, 16, 20, 36})
    {
        const int i {std::stoi("111", nullptr, base)};
        std::cout << "std::stoi('111', " << base << "): " << i << '\n';
    }
}

std::stoi('45'): 45; pos: 2
std::stoi('+45'): 45; pos: 3
std::stoi(' -45'): -45; pos: 4
std::stoi('3.14159'): 3; pos: 1
std::stoi('31337 with words'): 31337; pos: 5
std::stoi('words and 2'): ... std::invalid_argument::what(): stoi
std::stoi('12345678901'): ... std::out_of_range::what(): stoi
std::stoll('12345678901'): 12345678901; pos = 11
 
Calling with different radixes:
std::stoi('111', 2): 7
std::stoi('111', 3): 13
std::stoi('111', 4): 21
std::stoi('111', 8): 73
std::stoi('111', 10): 111
std::stoi('111', 12): 157
std::stoi('111', 16): 273
std::stoi('111', 20): 421
std::stoi('111', 36): 1333

See also