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.