std::atoi, std::atol, std::atoll - cppreference.com

Original:

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

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Original:

Function discards any whitespace characters until first non-whitespace character is found. Then it takes as many characters as possible to form a valid integer number representation and converts them to integer value. The valid integer value consists of the following parts:

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Original:

Integer value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, the return value is undefined. If no conversion can be performed, 0 is returned.

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#include <iostream>
#include <cstdlib>

int main()
{
    const char *str1 = "42";
    const char *str2 = "3.14159";
    const char *str3 = "31337 with words";
    const char *str4 = "words and 2";

    int num1 = std::atoi(str1);
    int num2 = std::atoi(str2);
    int num3 = std::atoi(str3);
    int num4 = std::atoi(str4);

    std::cout << "std::atoi(\"" << str1 << "\") is " << num1 << '\n';
    std::cout << "std::atoi(\"" << str2 << "\") is " << num2 << '\n';
    std::cout << "std::atoi(\"" << str3 << "\") is " << num3 << '\n';
    std::cout << "std::atoi(\"" << str4 << "\") is " << num4 << '\n';
}

std::atoi("42") is 42
std::atoi("3.14159") is 3
std::atoi("31337 with words") is 31337
std::atoi("words and 2") is 0