C strlen() Function

The strlen() function in C is used to determine the length of a string. It returns the number of characters in a string, excluding the null terminator ('0'). The string is passed to the function as a pointer to the first character of the string, and the function calculates the length until it encounters the null character.

Syntax of strlen()

The syntax of the strlen() function is as follows:

                        
size_t strlen(const char *str);
                  
                    

The function takes a single argument str, which is a pointer to the string whose length is to be determined. The return value is of type size_t, which is an unsigned integer representing the length of the string.

Example of strlen() Function

Here is an example that demonstrates how the strlen() function works:

                        
#include <stdio.h>
#include <string.h>
int main() 
{
   char str[] = "Hello, World!";
                
   // Calculating the length of the string
   size_t length = strlen(str);
                
   // Displaying the length
   printf("The length of the string is: %zu\n", length);
                
   return 0;
}
                        
                    

Explanation of the Example

In this example:

• We define a string str with the value "Hello, World!".
• We use the strlen() function to get the length of the string.
• The function returns 13 because there are 13 characters in the string, excluding the null character.
• Finally, the length is printed using printf().

                        
#include <stdio.h>
#include <:string.h>
int main() 
{
   char str[100];
   printf("Enter a string: ");
   fgets(str, sizeof(str), stdin);
    
   // Remove newline character added by fgets
   str[strcspn(str, "\n")] = '0';
    
   printf("The length of the string '%s' is: %zu\n", str, strlen(str));
   return 0;
}
                        
                    

Important Notes

• The strlen() function only works with null-terminated strings. If the string is not null-terminated, the result will be undefined.
• The function does not count the null terminator ('0') at the end of the string.