What is strtol in C?
The strtol library function in C converts a string to a long integer. The function works by ignoring any whitespace at the beginning of the string, converting the next characters into a long integer, and stopping when it comes across the first non-integer character.
Syntax
Here is how it is defined in C:
long int strtol(const char *str, char **endptr, int base);
Functions used to define it in C:
str: A pointer to the string that is to be converted to a long integer.endptr: A pointer used bystrtol, which points to the first non-integer character signaled to stop conversion.base: The base of the number being converted. It must be between 2 and 32, inclusive, or be a special value 0.
Note: If the base is 0, the number is assumed to be a decimal, unless, the converted number starts with O (for Octal) or Ox (for hexadecimal).
Examples
1. String to long integer conversion
A simple conversion from a string, to a long integer, works like this:
#include <stdlib.h> // the library required to use strtolint main() {char str[50] = "2020111224234234";char *remaining;long answer;answer = strtol(str, &remaining, 10);printf("The converted long integer is %ld\n", answer);return 0;}
2. String with whitespace and characters to long integer
This example highlights how
strtol ignores whitespaces at the start, and also stores the rest of the string in remaining.
#include <stdlib.h> // the library required to use strtolint main() {char str[50] = " 90908752 rest of the string";char *remaining;long answer;answer = strtol(str, &remaining, 10);printf("The converted long integer is %ld\n", answer);printf("The string part was: %s. ", remaining);return 0;}
3. String to hexadecimal conversion
Here’s how to convert a string to hexadecimal. Note that the base argument strtol is set to 16, which is the base for hexadecimals.
#include <stdlib.h> // the library required to use strtolint main() {char str[50] = "0x85fa4b";char *remaining;long answer;answer = strtol(str, &remaining, 16);printf("The converted hexadecimal is %lx\n", answer); // %lx is the format for hexadecimalsreturn 0;}
Free Resources
