Declare variables at top of function or in separate scopes?

Question

Which is preferred, method 1 or method 2?

Method 1:

LRESULT CALLBACK wpMainWindow(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
    switch (         


        

Answer 1

Memory allocation is not specified in the Standard to this detail, so for a real answer you'll have to specify compiler and platform. It's not going to matter for performance.

What you want is readability, and in general that's done by declaring variables in the smallest usable scope, and preferably when you can immediately initialize them with reasonable values. The smaller a variable's scope, the less it can potentially interact with the rest of the program in unpredictable ways. The closer the declaration to initialization, the less opportunity for anything bad to happen.

What would probably be better is something like

RECT rc;
GetClientRect(hwnd, &rc);
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);

This is for C++. For C, the rule is similar, except that earlier versions of C required all the variables to be declared at the top of a block.