WINAPI identifiers in function declaration C++ in DLL entrypoint function

Question

I'm just learning how to create a dll with C++.

There appears this :

BOOL WINAPI DllMain(HINSTANCE hinstDLL,DWORD fdwReason,LPVOID lpvReserved)

And I can not understand what is "WINAPI" in DllMain()?

I know that a function is :

typeReturn functionName (params) { function body }

typeReturn : is the value that function returns,
functionName : is the name of the function,
params : are the parameters for the function,
{function body} : is the code inside in the function.
...

Then, following the explanation, what does WINAPI mean in C++ that or __stdcall?

I'm not asking what means WINAPI itself.

************ UPDATE **************

C++ has (calling conventions) that is used to put in memory each parameter given in a special way. please read correctly the question and avoid mark it as duplicate, because people learning c/c++ needs learn without fall into confusions

For me, searching "WINAPI" in Google gives the answer in the first link: https://stackoverflow.com/questions/2348442/what-does-winapi-in-main-function-mean — Ivan Aksamentov - Drop, Aug 19 '18 at 04:14
yes, but what does IN C++ mean? can i write functions with extra identifier that crowns functions? — Andres Camilo Sierra Hormiga, Aug 19 '18 at 04:20

BattleTested_закалённый в бою · Accepted Answer · 2018-08-19T11:16:27.507

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WINAPI is defined as __stdcall.

Actually __stdcall is a calling convention And different calling conventions push parameters in different ways, Bellow are some of c/c++ Calling Conventions :

In x86 :

C calling convention (__cdecl). The main characteristics of __cdecl calling convention are :
1. Arguments are passed from right to left, and placed on the stack.
2. Stack cleanup is performed by the caller.
3. Function name is decorated by prefixing it with an underscore character '_' .
Standard calling convention (__stdcall). The main characteristics of __stdcall calling convention are :
1. Arguments are passed from right to left, and placed on the stack.
2. Stack cleanup is performed by the called function.
3. Function name is decorated by prepending an underscore character and appending a '@' character and the number of bytes of stack space required.
Fast calling convention (__fastcall). he main characteristics of __fastcall calling convention are :
1. The first two function arguments that require 32 bits or less are placed into registers ECX and EDX. The rest of them are pushed on the stack from right to left.
2. Arguments are popped from the stack by the called function.
3. Function name is decorated by by prepending a '@' character and appending a '@' and the number of bytes (decimal) of space required by the arguments.

Consider to Read This Link

In x64 : In x64, only __fastcall exists. All other attributes are ignored.

The x64 Application Binary Interface (ABI) uses a four register fast-call calling convention by default.

Notice : When you call a function, what happens at the assembly level is all the passed-in parameters are pushed to the stack or placed in registers or placed in static storage, then the program jumps to a different area of code. The new area of code looks at the stack and expects the parameters to be placed there.

Different calling conventions push parameters in different ways. Some might push the first parameter first, or some might push the first param last. Or some might keep a parameter in a register and not push it at all.

By specifying a calling convention, you are telling the compiler how the parameters are to be pushed.

edited Aug 19 '18 at 11:16

answered Aug 19 '18 at 04:18

BattleTested_закалённый в бою

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so, PARAMETERS can be passed to stack, why? or why do i need push parameters to another site? sorry, i'm very new in c++. – Andres Camilo Sierra Hormiga Aug 19 '18 at 04:32
The `__cdecl` convention is "safer" because it is the caller that needs to deallocate the stack. What may happen in a `__stdcall` library is that the developer might have forgotten to deallocate the stack properly, or an attacker might inject some code by corrupting the DLL's stack (e.g. by API hooking) which is then not checked by the caller. See this [Link](https://stackoverflow.com/questions/6511096/cdecl-or-stdcall-on-windows) – BattleTested_закалённый в бою Aug 19 '18 at 04:37
then, "calling conventions" in C++ are a safer way to call functions, avoiding some attackers inject code to corrupt my function. searching in google... – Andres Camilo Sierra Hormiga Aug 19 '18 at 04:45
"pushed to the stack" or placed in registers or placed in static storage... Not sure if I should downvote, so I choose not to. But please do fix. – Cheers and hth. - Alf Aug 19 '18 at 04:54
@Cheersandhth.-Alf do you mean i refer to "or placed in registers or placed in static storage" in my answer? – BattleTested_закалённый в бою Aug 19 '18 at 05:07
@Cheersandhth.-Alf fixed – BattleTested_закалённый в бою Aug 19 '18 at 05:10
You might add some sentences about cleaning up the stack again, too, as there are differences as well (e. g. cdecl: caller; stdcall: callee). – Aconcagua Aug 19 '18 at 05:11
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@AndresCamiloSierraHormiga Calling conventions in general aren't a "safer" way to call functions. _Every_ function has a calling convention. It's the contract between the caller and the callee that both agree to adhere to so that the callee knows where to find its parameters and where to put its return value so the caller can find it. – Miles Budnek Aug 19 '18 at 05:23
@Miles Budnek you're right. guys i found: https://stackoverflow.com/questions/949862/what-are-the-different-calling-conventions-in-c-c-and-what-do-each-mean ... at the second answer, that is an explaination about cdecl, fastcall, etc. – Andres Camilo Sierra Hormiga Aug 19 '18 at 05:29
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Worth noting, those calling conventions are relevant in 32-bit code only. The 64-bit ABI of the Windows API defines only a single calling convention, and you can get away with not specifying one in your code, because the choice is unambiguous. – IInspectable Aug 19 '18 at 07:04
decoration, which you describe, is only for *x86* platform and only for *extern "C"* funtions – RbMm Aug 19 '18 at 08:33
@RbMm Fixed.... – BattleTested_закалённый в бою Aug 19 '18 at 11:17

score 0 · Answer 2 · answered Aug 19 '18 at 04:17

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Dynamic-Link Library, used in Windows operating system, so the entry point of DLL function should be crowned by "WINAPI" if it is running on Windows.

answered Aug 19 '18 at 04:17

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WINAPI identifiers in function declaration C++ in DLL entrypoint function

2 Answers2