The function atol converts a string to a long integer(long int). The function skips all white-space characters at the beginning of the string until the first non-whitespace character is found. Then it converts the subsequent characters into a long integer number until it finds a character which is not a digit. It also takes an optional initial plus or minus sign before first base-10 digit in string.
Function prototype of atol
long int atol(const char *str);
- str : A pointer to a string beginning with the representation of an long integer number.
Return value of atol
The function returns the converted integer number as a long int value otherwise it returns zero(0), If no valid conversion could be performed.
C program using atol function
The following program shows the use of atol function for string to long integer conversion.
#include <stdio.h>
#include <stdlib.h>
int main(){
char string[100];
long value;
printf("Enter a string\n");
scanf("%s", &string);
/* String to Long integer conversion */
value = atol(string);
printf("Long value %ld\n", value);
return 0;
}
Output
Enter a string 1234 Long value 1234
Enter a string 1234.555 Long value 1234
Enter a string 1234ABCD Long value 1234
Enter a string ABCD Long value 0