What do __cdecl and (void) mean?

Question

I'm currently programming a tcp/ip server using WSA. After some troubleshooting a friend of mine said that i should use bool __cdecl winsock_server ( void ) instead of bool winsock_server().

But he didn't explain to me what __cdecl and (void) are doing. I already know that __cdecl changes the way how arguments are put on the stack on assembler level, but what does (void) mean?

I should point out that I'm new to C++. I only programmed in C# and VB.NET before.

Thanks in advance!

They do nothing useful. `__cdecl` is already the default calling convention for free functions, in C++ member functions are `__thiscall` and cannot be `__cdecl`. Do not confuse it with `extern "C"` like the upvoted answer did. `(void)` is only useful in C to emphasize that the function has zero arguments. — Hans Passant, Jun 06 '19 at 06:56

Gyapti Jain · Accepted Answer · 2019-06-06T14:35:25.443

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__cdecl
You got it right. It enforces function calling convention to c-style and thus the way function is called (How arguments are passed, who cleans stack). BTW this is already default calling convention.

(void) v/s ()
In C++ they are equivalent(no arguments).
In C however former means no arguments and latter means any number of arguments. So it can cause problems when you reuse the header file for C.

edited Jun 06 '19 at 14:35

answered Jun 06 '19 at 06:18

Gyapti Jain

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do i get any advantages when using __cdecl ? – AcrimEx Jun 06 '19 at 06:21
@Th3Bamb00zl3r Yes, you get compatibility with 'C'. About the performance, there may be arguments on either side. (cdecl stands for c declaration) – Gyapti Jain Jun 06 '19 at 06:23
cdecl ain't extern C, see https://learn.microsoft.com/en-us/cpp/cpp/cdecl?view=vs-2019 – JVApen Jun 06 '19 at 07:23
@JVApen `__cdecl` is C calling convention. Both C and C++ symbols(functions and variable names) may use it. `extern C` is a C++ thing that suggests C++ compiler not to do name-mangling in C++ way. (C way is just an underscore before function name which is enough as function overloading is not supported). C++ declaration may use both or one or none according to the requirements. – Gyapti Jain Jun 06 '19 at 09:14

score 0 · Answer 2 · answered Jun 06 '19 at 06:18

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(void) means it has no arguments. It's more of a code style thing. you could use only () but writing (void) explicitly shows that the function have no arguments.

answered Jun 06 '19 at 06:18

Niek Nooijens

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`()` also shows that the function has no arguments in C++. – melpomene Jun 06 '19 at 06:54
yeah but writing (void) makes it more explicit. it's a code style thing. the compiler won' t care. – Niek Nooijens Jun 06 '19 at 07:49
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It's only "more explicit" if you're coming from C. In all other languages an empty parameter list means an empty parameter list. I don't think it's idiomatic C++. – melpomene Jun 06 '19 at 07:52
@Niek: Yes it will – Lightness Races in Orbit Jun 06 '19 at 14:53
@melpomene It's because I read your comment as "in C" rather than "in C++" somehow – Lightness Races in Orbit Jun 06 '19 at 16:56
It is NOT only a coding style thing! Writing function(void) means a function with no parameters (parameter type list is void), whereas function() *could* mean a function with multiple parameters; the amount is determined by the initializer list, not the parameter type list. I learned about this here: https://jameshfisher.com/2016/11/27/c-k-and-r/ – Bert Regelink Oct 20 '22 at 11:18

What do __cdecl and (void) mean?

2 Answers2