Learning reversing via C++, but what does this line do?

typedef int(__stdcall *__MessageBoxA)(HWND, LPCSTR, LPCSTR, UINT); 

As I said, im trying to learn how to reverse engineer programs using C++ / Assembly, so I'm going through some open source projects I found on the internet. But can anyone explain what this line does? Im not advanced in C++, which is why I'm going through sources.

Your code is C language. So it also compiles fine in C++.

Let 's go step by step.

1. Here is a function declaration or prototype or signature.
   It returns an int, accepts 4 parameters :

int __stdcall MessageBoxA(HWND, LPCSTR, LPCSTR, UINT); 

2. Here ptr is a pointer variable to a function :

int(__stdcall *ptr)(HWND, LPCSTR, LPCSTR, UINT); 
ptr = NULL;
/ assign a correct adress
ptr = MessageBoxA;
// call the function with parameters using the pointer
(*ptr)(hWnd, NULL, NULL, 0); 

3. Here __MessageBoxA is a type that helps to define a variable that is a pointer to a function:

typedef int(__stdcall *__MessageBoxA)(HWND, LPCSTR, LPCSTR, UINT); 

So a pointer to a function variable can be declared.

__MessageBoxA ptr1 = NULL;

__stdcall is the way the function is called by the compiler ( Are parameters passed from left to right or reverse ? Is return value passed through stack memory or CPU register ?) - details most people don't care as long as caller and called agree

Regards