如何将 C 样式数组复制到 C++ 中的空指针中？

Question

So basically I've recently started coding in C++ instead of C so maybe that's not the C++ way of doing this, but I've got a program where the user passes an array as a function parameter ( void foo(void* pass_array_here) ) and I want to copy it in a private member of a class, also declared as void* array_private . I'm copying it like this:

void foo(void* pass_array_here) {
    array_private = pass_array_here;
}

I must note that I'm working with OpenGL so I don't know if I can rely on the new keyword or the heap in general. So how do I do that?

(Note, on a sizeof call, a 9-element float array appeared as 8 bytes in the stack, so it definitely didn't work).

Answer 1

1. As already commented above, using void* is not very useful.
2. If you need an array object, it's recommended in C++ to use either std::array for a fixed size array, or std::vector for dynamic size array.
3. This line: array_private = pass_array_here is simply assigning the pointer, not copying the array content.
4. If you use std::array or std::vector as suggested in point 2 above, you can utilize the copy constructor of these classes to actually copy the array's content easily:

    void foo(std::vector<SomeType> const & pass_array_here) {
        array_private = pass_array_here;
    }

5. If the caller of the function foo does not need to use the array after calling the function, you can save the copy of the data, and utilize C++ move semantics (available since C++ 11):

    void foo(std::vector<SomeType> && pass_array_here) {
        array_private = std::move(pass_array_here);
    }

6. If the caller does not have a std::vector but an old C style array, it is possible to initialize the std::vector member from it (which will copy the data). See: std::vector::assign .

For 4, 5 and 6 above, your private data member will have to be defined as:

std::vector<SomeType> array_private; 

7. If you need to access the data buffer managed by an std::vector , you can use std::vector::data : std::vector::data . You can cast this data pointer into a void* if you need to pass it to a C style function, eg in opengl (no need to copy the data).

8. More about move semantics and R value references here: Understanding rvalue references