MingW Header Files Have No Labels

Question

I've installed vscode extension (ms-vscode.cpptools) from Microsoft to enable intellisense. But, when i typed MessageBox, the parameters have no labels.

It should be

MessageBoxW(HWND hWnd, LPCWSTR lpText, LPCWSTR lpCaption, UINT uType)

My Question: Why MingW distribute the header files without labels?

Answer 1

It should be

MessageBoxW(HWND hWnd, LPCWSTR lpText, LPCWSTR lpCaption, UINT uType)

That is not so.

The tooltip is showing you the declaration of the function, as declared in MingGW's header winuser.h. That declaration specifies the function's prototype, consisting of:

• The return type of the function, then
• The name of the function, then
• The types of the parameters in the parameter-list, within brackets, in the right order.

as the tooltip does:

int MessageBoxW (HWND, LPCSTR, LPCSTR, UINT)

What you call "labels" are parameter-names. They are optional, and redundant, in a function declaration, since the compiler does not need them to understand how the declared function will be called, and what it returns. MessageBoxW is to be called with arguments that are a HWND, a LPCSTR, another LPCSTR, and a UINT, in that order; and it returns and int.

The compiler requires parameters to be named in a function definition:

add.c

// definition

int add(int x, int y)
{
    return x + y;
}

main.c

#include <stdio.h>

extern int add(int,int); // Declaration

int main()
{
    printf("%d\n",add(3,4));
    return 0;
}

Compile with maximum strictness, link and run:

$ gcc -Wall -Wextra -pedantic -o prog main.c add.c
$ ./prog
7

See also Function Declaration in C

Parameter-names are useful to human readers in a function-declaration when the declaration is accompanied by documentation of the function, since the documentation can then refer to the parameter-names to explain the function's behaviour:

/*
    Return the sum of `x` and `y`
*/
int add(int x, int y);

But they are unnecessary to the compiler.

Like the MinGW windows headers, Micorosoft's own headers do not contain comments to document the APIs, but they do contain parameter-names, and also SAL Annotations of the parameter names. E.g. in Microsoft's WinUser.h (SDK 2017) the declaration of MessageBoxW is:

int
WINAPI
MessageBoxW(
    _In_opt_ HWND hWnd,
    _In_opt_ LPCWSTR lpText,
    _In_opt_ LPCWSTR lpCaption,
    _In_ UINT uType);

The SAL annotations, (_In_opt_, _In_ and similar) are a non-standard Microsoft language extension that supports static analysis of the correctness of code implementing or invoking the APIs and they are used for that purpose by Microsoft's compilers.

Such SAL-based static analysis needs names for the annotated parameters in order to provide meaningful diagnostics; hence the parameters have names in the annotated declarations in Microsoft's headers.

GCC, including MinGW ports, does not support SAL; so parameter names remain redundant in function declarations.