C strlen()

The strlen() function takes a string as an argument and returns its length. The returned value is of type size_t (an unsigned integer type).

It is defined in the <string.h> header file.

Example: C strlen() function

#include <stdio.h>
#include <string.h>
int main()
{
    char a[20]="Program";
    char b[20]={'P','r','o','g','r','a','m','\0'};

    // using the %zu format specifier to print size_t
    printf("Length of string a = %zu \n",strlen(a));
    printf("Length of string b = %zu \n",strlen(b));

    return 0;
}

Output

Length of string a = 7
Length of string b = 7

Note that the strlen() function doesn't count the null character \0 while calculating the length.