How it is possible to have entry point other than main(), in Win32 projects in C++. (WinMain)

Question

From the books i have read about C and C++ I understood that the entry point in C program must be main.Till now i had made only console applications and now im starting to learn about windows applications. So my questions is :

Why the entry point in Win32 project is not main (but WinMain) and how is it possible to be different ( maybe main calls WinMain ?) ?

ps. Sorry for bad english

Possible duplicate of [WinMain vs. main (C++)](https://stackoverflow.com/questions/18709403/winmain-vs-main-c) — phuclv, Feb 18 '18 at 00:32

score 4 · Answer 1 · answered Feb 17 '18 at 23:09

4

It is true that C++ requires main to be the "entrypoint" of the program, at least under what's called "hosted implementations" (the ones you're probably using). This is why you get a linker error with GCC if you forgot to define a main.

However, in practice, the gap where your program ends and the "runtime" begins, makes things seem a little more wooly — when your program is launched, the first functions called are actually inside the runtime, which will eventually get around to invoking main. It is actually this invocation which causes the linker error if you forgot to define a main.

Microsoft has decided that, for Windows GUI programs, instead of invoking main, their runtime will invoke WinMain. As a consequence, you have to define a function WinMain for it to find, instead of main. Technically this violates the C++ standard, but it works because Microsoft makes it work.

answered Feb 17 '18 at 23:09

Lightness Races in Orbit

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It's more than a convention. It's a requirement for programs compiled with the MS linker and working with the MS runtime. – Sebastian Redl Feb 17 '18 at 23:41
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Windows GUI programs are non-portable anyway so the fact that Microsoft has a non-standard entry point for them is not a big deal... I think... – bolov Feb 17 '18 at 23:51
@bolov: I concur. – Lightness Races in Orbit Feb 18 '18 at 00:23
@SebastianRedl: Is that not what I said? – Lightness Races in Orbit Feb 18 '18 at 00:23
@LightnessRacesinOrbit I was replying to a now-deleted comment. – Sebastian Redl Feb 18 '18 at 10:00
@SebastianRedl: Yours was the first comment on this answer. Are you sure you weren't intending to reply on Remy's? I talked about convention in a deleted comment there (although, again, saying the exact same thing as you) – Lightness Races in Orbit Feb 18 '18 at 14:08
I'm 90% sure I was replying to a comment on your post. – Sebastian Redl Feb 18 '18 at 16:27
@SebastianRedl: You must have hopped parallel universes For the record, my comment under Remy's answer was something along the lines of "the standard requires blah blah blah, so it's a little more than a convention, but not by much" – Lightness Races in Orbit Feb 18 '18 at 17:00
The comment I replied to was short, just "So it's just a convention." or something similar. – Sebastian Redl Feb 18 '18 at 17:08
@SebastianRedl: Okay I must have missed it then. No worries – Lightness Races in Orbit Feb 18 '18 at 18:02

Remy Lebeau · Answer 2 · 2018-02-17T22:57:38.257

The actual name and signature of the entry point in your code is dictated by the runtime framework you decide to use inside your EXE.

When the OS executes an EXE, it first calls an entry point specified in the EXE header by the linker, and is usually located in the compiler vendor's runtime library.

The runtime library's entry point initializes the library, sets up globals, etc, and then finally calls an entry point that your code must implement (the runtime library contains a reference to an external entry point, and the linker hooks up your code's entry point to that reference).

So, your code's entry point is whatever the runtime library requires it to be. The standard entry point for console apps in C/C++ is main, and the traditional entry point for Windows GUI apps is WinMain. But this is not a requirement as far as the OS is concerned.

score 1 · Answer 3 · answered Feb 17 '18 at 23:37

In fact main is just a name look at assembly language: you are free to declare your Entry Point as you want eg:

.code

START:
ret
END START

But in C++ it doesn't allow you to define your own EP. So must implement the convention: for console you need main, wmain, win32: WinMain, for Dll: dllmain...

How it is possible to have entry point other than main(), in Win32 projects in C++. (WinMain)

3 Answers3