It's worth remembering that Windows 1.x and 2.x predates the C89 standard. This also explains why WINAPI calling convention was inherited from Pascal instead of C. The C standard library was "just another competitor" at the time.

The WINAPI calling convention is a cross between C and Pascal - C-style order of arguments on the stack, but Pascal-style callee cleaning the stack before return.

The reason for its use in Windows is that it makes generated code slightly smaller and more efficient, at the cost of not supporting varags easily (which you don't need for most functions anyway). Back when you had 640 Kb of RAM, saving a few bytes here and there adds up quickly.

Those functions explicitly? I can't find any definitive explanation on why they exist.

It looks like nowdays ZeroMemory() and RtlZeroMemory() are just macros for memset().

Here's an article on some of the RECT helper functions. Relevant for the 8088 CPU but probably not so much today: https://devblogs.microsoft.com/oldnewthing/20200224-00/?p=10...

Windows didn't standardize on C. It was mostly assembly and some Pascal in the beginning with C and C++ later.

Microsoft have always viewed C as just another language, it's not privileged in the way UNIX privileges C. By implication, the C standard library was provided by your compiler and shipped with your app as a dependency on Windows, it wasn't provided by the operating system.

These days that's been changing, partly because lots of installers dumped the MSVC runtime into c:\windows\system and so whether it was a part of the OS or not became blurred and partly because Microsoft got more willing to privilege languages at the OS level. Even so, the Windows group retains a commitment to language independence that other operating systems just don't have. WinRT comes with lots of metadata for binding it into other languages, for example.

> Windows didn't standardize on C. It was mostly assembly and some Pascal in the beginning with C and C++ later.

No, it was never Pascal. It was always C from the beginning. You may have been confused by them using the Pascal calling convention because it was generally faster on the 16-bit CPUs of the time.

Apple was the one going with Pascal for the OS, originally the Object Pascal linage was started at Apple, in collaboration with Niklaus Wirth that gave feedback on the design.

You could write code without using libc / the C runtime. You still can.

Unlike Unix, Windows historically didn't have a standard C runtime at all. Stuff like MSVCRT.DLL etc came later (and are themselves implemented on top of Win32 API, not directly on top of syscalls as is typical in Unix land).