atol() is a Utility Function that converts a string into a long value. The string must contain a valid long integer value, the rest of the string characters are terminated by white space, punctuation, characters. If a long integer is not found the result may be undefined, but in most scenarios will return 0.

    int atol(const char *str);

   #include <stdlib.h>
   #include <iostream.h>
   int main()
     {
        char arr[10];
        cout << "Enter a string with a long integer:: ";
        cin >> arr;
        cout << "Value returned by atol is:: " << atoi(arr) <<'\n';
        cout << "Bytes occupied is:: " << sizeof(atoi(arr));
     }

   Enter a string with a long integer:: 134.56
   The entered value is:: 134
   The bytes occupied is:: 4

In the above example atol() is used to return the long value as "134" leaving the decimal ".56".