CODEWITHSUNDEEP
c++
bartop
bartop

Reputation: 10315

Version of std::stoi rejecting any non-number

As you may know, std::sto* function family works in a way that reads number in string until it finds non-number, like that:

std::string pseudoNum = "123haha";
int num = std::stoi(pseudoNum); //no problem, num = 123

Is there any standard way to have more strict integer parsing, which causes exception/error code return in such situations (when string is not completely integer)?

Upvotes: 4

Views: 654

Answers (3)

NutCracker
NutCracker

Reputation: 12263

You can use C++17's std::from_chars and check the length of the parsed value:

#include <iostream>
#include <charconv>

int main() {
    const std::string str { "123haha" };
    int value = 0;
    const auto result = std::from_chars(str.data(), 
                                        str.data() + str.size(), 
                                        value);

    if (result.ec == std::errc()) {
        std::cout << "Value: " << value << std::endl;
        std::cout << "Length: " << result.ptr - str.data() << std::endl;
    }

    return 0;
}

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C++11 solution

A second parameter to std::stoi is an address of an integer to store the number of characters processed.

#include <iostream>

int main() {
    const std::string str { "123haha" };
    std::size_t processed_chars = 0;
    int value = std::stoi(str, &processed_chars);

    std::cout << "Value: " << value << std::endl;
    std::cout << "Length: " << processed_chars << std::endl;

    return 0;
}

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Upvotes: 2

Evgeny
Evgeny

Reputation: 1072

Doesn't the second argument suite you? Second argument of std::stoi is very usefull for that: if returned position is equills the size of the string then whole string is a number.

Upvotes: 1

Raz Rotenberg
Raz Rotenberg

Reputation: 609

The second argument of std::sto*() methods is std::size_t * pos which will be set to the number of numeric characters used for the conversion (can be seen here).

This is how I implemented this:

int my_stoi(const std::string & str)
{
    std::string::size_type pos;
    const int value = std::stoi(str, /* out */ &pos);

    if (pos != str.size())
    {
        std::cerr << "Failed parsing string '" << str << "' as an integer" << std::endl;
    }

    return value;
}

Upvotes: 1

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