how to get char length in c++ code example

Example 1: c++ length of char*

#include <iostream>
#include <string.h>

using namespace std;

int main()
{
    char *str = "ABC";
    cout << strlen(str) << endl;
    return 0;
}

Example 2: char size length c++

char* a = "ABC";
int length = sizeof(a)/sizeof(char);