# std::atoi, std::atol, std::atoll

From cppreference.com
< cpp‎ | string‎ | byte

Defined in header `<cstdlib>` |  |
int atoi( const char *str ); |  |
long atol( const char *str ); |  |
long long atoll( const char *str ); |  | (since C++11)

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

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

- (optional) plus or minus sign
- numeric digits

### Parameters

str | - | pointer to the null-terminated byte string to be interpreted

### Return value

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.

### Example

Run this code

    #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';
    }

Output:

    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

### See also

stoistolstoll (C++11)(C++11)(C++11) | converts a string to a signed integer (function)
strtolstrtoll | converts a byte string to an integer value (function)
strtoul strtoull | converts a byte string to an unsigned integer value (function)

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