What is atol() in C++?
The atol() function in C++ is used to convert a string to an integer data-type long int. atol() interprets the contents of the string as an integer.
Library
To use the atol() function, include the following library:
#include <cstdlib>
Declaration
The atol() function can be declared as:
long int atol(const char* str);
str: The string to be converted to an integer.
Return value
The atol() function returns a long int type variable that is the integer interpretation of the string str.
Note: The
atol()function returns 0 if:
stris empty.strcontains only whitespace characters.- The sequence of non-whitespace characters in
stris not a valid integer.- Non-numeric characters are placed before numeric characters.
Examples
Example 1
Consider the code snippet below, which demonstrates the use of the atol() function:
#include <cstdlib>#include <iostream>using namespace std;int main(){char str1[] = "123";char str2[] = "-123";char str3[] = "12end with words";long int asint1 = atol(str1);cout<<"atol( "<<str1<<" ) = "<<asint1<<endl;long int asint2 = atol(str2);cout<<"atol( "<<str2<<" ) = "<<asint2<<endl;long int asint3 = atol(str3);cout<<"atol( "<<str3<<" ) = "<<asint3<<endl;return 0;}
Explanation
Three strings, str1, str2, and str3, are declared in lines 8-10. The atol() function is used in line 12, line 15, and line 18 to convert str1, str2, and str3 to integers, respectively.
Example 2
Consider the code snippet below, which demonstrates when the atol() function returns 0:
#include <cstdlib>#include <iostream>using namespace std;int main(){char str1[] = "";char str2[] = " \t ";char str3[] = "abc";char str4[] = "start with words12";long int asint1 = atol(str1);cout<<"atol( "<<str1<<" ) = "<<asint1<<endl;long int asint2 = atol(str2);cout<<"atol( "<<str2<<" ) = "<<asint2<<endl;long int asint3 = atol(str3);cout<<"atol( "<<str3<<" ) = "<<asint3<<endl;long int asint4 = atol(str4);cout<<"atol( "<<str4<<" ) = "<<asint4<<endl;return 0;}
Explanation
Four strings, str1, str2, str3, and str4, are declared in lines 8-11.
- line 13: The
atol()function is used to convertstr1to an integer. Theatol()function returns 0, asstr1is empty. - line 16: The
atol()function is used to convertstr2to an integer. Theatol()function returns 0, asstr2only contains whitespace characters. - line 19: The
atol()function is used to convertstr3to an integer. Theatol()function returns 0, as non-whitespace characters ofstr3do not represent a valid integer. - line 22: The
atol()function is used to convertstr4to an integer. Theatol()function returns 0, as non-numeric characters are placed before numeric characters ofstr4.
