将C＃哈希函数转换为C ++

Question

I have this function in C#:

public static unsafe int GetMonoHash(string str) {
    unsafe {
        fixed (char* src = str) {
            char* chPtr2 = src; // + offset;
            char* chPtr3 = (chPtr2 + str.Length) - 1;
            int num = 0;
            while (chPtr2 < chPtr3) {
                num = ((num << 5) - num) + chPtr2[0];
                num = ((num << 5) - num) + chPtr2[1];
                chPtr2 += 2;
            }
            chPtr3++;
            if (chPtr2 < chPtr3) {
                num = ((num << 5) - num) + chPtr2[0];
            }
            return num;
        }
    }
}

I tried to rewrite it in C++ and I got this far:

int Utils::getMonoHash(std::string str)
{
    char* src = &str[0];
    char* chPtr2 = src; // + offset;
->  char* chPtr3 = (chPtr2 + str.length) - 1;
    int num = 0;
    while (chPtr2 < chPtr3) {
        num = ((num << 5) - num) + chPtr2[0];
        num = ((num << 5) - num) + chPtr2[1];
        chPtr2 += 2;
    }
    chPtr3++;
    if (chPtr2 < chPtr3) {
        num = ((num << 5) - num) + chPtr2[0];
    }
    return num; 
}

This was throwing a compilation errors:

C3867 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>::length': non-standard syntax; use '&' to create a pointer to member
C2297 '+': illegal, right operand has type 'unsigned __int64 (__cdecl std::basic_string<char,std::char_traits<char>,std::allocator<char>>::* )(void) noexcept const'

So I changed the indicated ( -> ) line to

char* chPtr3 = (chPtr2 + (char *)str.length) - 1;

which gave me a new compilation error (just one this time, yay!):

C2440 'type cast': cannot convert from 'unsigned __int64 (__cdecl std::basic_string<char,std::char_traits<char>,std::allocator<char>>::* )(void) noexcept const' to 'char *'

I have no idea what to do now. I need the C++ function to have the same output as the C# one when given the same input as the C# one.

What do I do here?

Answer 1

str.length is not a property, it is a function and needs ()

In my experience as a C# programmer, this is one of the most common mistakes C# programmers make when writing C++.

Answer 2

Don't forget parenthesis after str.length. Correct type should be like this

char* chPtr3 = (chPtr2 + str.length()) - 1;

Answer 3

What do you do? You stop "translating" as if C++ and C# have anything in common, and write from scratch using your base requirements — and your C++ book — as a guide.

In this case your problem is that you are using a member function incorrectly. It is str.length() . The compiler's complaints are about using a function name incorrectly, without actually calling it.