Question

I’m trying to understand un-managed code. I come from a background of C# and I’m playing around a little with C++.

Why is that this code:

#include <iostream>

using namespace std;

int main()
{
    char s[] = "sizeme";

    cout << sizeof(s);

    int i = 0;
    while(i<sizeof(s))
    {
        cout<<"\nindex "<<i<<":"<<s[i];
        i++;
    }
    return 0;
}

prints out this:

7
index 0:s
index 1:i
index 2:z
index 3:e
index 4:m
index 5:e
index 6:

????

Shouldn’t sizeof() return 6?

Answer 1

C strings are “nul-terminated” which means there is an additional byte with value 0x00 at the end. When you call sizeof(s), you are getting the size of the entire buffer including the nul terminator. When you call strlen(s), you are getting the length of the string contained in the buffer, not including the nul.

Note that if you modify the contents of s and put a nul terminator somewhere other than at the end, then sizeof(s) would still be 7 (because that’s a static property of how s is declared) but strlen(s) could be somewhat less (because that’s calculated at runtime).