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

< 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


[edit] Parameters

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

[edit] Return value

Integer value corresponding to the contents of str on success.

If no conversion can be performed, 0 is returned.

If the value of the result cannot be represented, i.e. the converted value falls out of range of the corresponding return type, behavior is undefined.

[edit] Example

#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

[edit] See also

converts a string to a signed integer
(function) [edit]
converts a string to an unsigned integer
(function) [edit]
converts a byte string to an integer value
(function) [edit]
converts a byte string to an unsigned integer value
(function) [edit]
converts a byte string to std::intmax_t or std::uintmax_t
(function) [edit]
converts a character sequence to an integer or floating-point value
(function) [edit]
C documentation for atoi, atol, atoll