Is this how the size() function really works in std::string?

Question

I wrote a simple function that can get the size of a std::string class object, and I know that size() function in std::string does the same job, So I wanted to know if the size() function really works like my function or if it is more complicated? If it's more complicated, then how?

int sizeOfString(const string str) {
    int i=0;
    while (str[i] != '\0') {
        ++i;
    }
    return i;
}

Answer 1

An std::string can contain null bytes, so your sizeOfString() function will produce a different result on the following input:

std::string evil("abc\0def", 7);

As for your other question: the size() method simply reads out an internal size field, so it is always constant time, while yours is linear in the size of the string.

You can peek at the implementation of std::string::size for various implementations for yourself: libc++, MSVC, libstdc++.