what the heck is __stdcall about?

User 3037427

Nibu babu thomas

sruti_p wrote:

what the heck is __stdcall about?

Hehe nice way to ask?:rolleyes: Calling conventions demystified[^] by Nemanja.

Nibu thomas A Developer Programming tips[^] My site[^]

Hamid Taebi

See Calling Convetions in Microsoft Visual C++[^]_**

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whitesky

Smith

__cdecl is the default calling convention for C and C++ programs. The advantage of this calling convetion is that it allows functions with a variable number of arguments to be used. The disadvantage is that it creates larger executables. __stdcall is used to call Win32 API functions. It does not allow functions to have a variable number of arguments. __fastcall attempts to put arguments in registers, rather than on the stack, thus making function calls faster. Thiscall calling convention is the default calling convention used by C++ member functions that do not use variable arguments. What's "variable number of arguments" ?? means Overloaded functions? And about _fastcall, if it's going to be faster, why not use it for every function we create? can you tell me about , where a particular convention must be used strictly. (yes, I've not gone through the article fully, but if you can explain please do) :)

Steve S

Variable number of arguments: Think printf, where you can pass one or more arguments, and the format control string determines how many arguments there are (hopefully correctly!). fastcall wouldn't be suitable for functions that take more than two or three arguments, and in some cases might be slower; there aren't an unlimited number of registers on a 32 bit processor. Generally, you don't need to specify the calling convention, but in some cases, you do, simply to ensure that the function has the one expected. Good examples are the functions you pass to things like qsort() and _beginthreadex(). Steve S Developer for hire

Smith

thanks :) NULL

Nibu babu thomas

Meat Loaf wrote:

What's "variable number of arguments" ?? means Overloaded functions?

You must have used printf, sprintf, fprintf, scanf, sscanf etc. They all take variable number of arguments. Take a look at va_start, va_end, va_arg. __cdecl calling convention specifies that the caller has to clean up the stack leading to larger executable size. Hence permitting the use of variable number of arguments.

Meat Loaf wrote:

__stdcall is used to call Win32 API functions. It does not allow functions to have a variable number of arguments.

Yeah true. For eg: WINAPI, PASCAL are #defined to be __stdcall. This is windows specific. This means the callee has to clean up the stack just before the callee returns hense variable number of arguments cannot be used here.

Meat Loaf wrote:

__fastcall attempts to put arguments in registers, rather than on the stack, thus making function calls faster.

Meat Loaf wrote:

And about _fastcall, if it's going to be faster, why not use it for every function we create?

Because we have limited number of registers.

Meat Loaf wrote:

can you tell me about , where a particular convention must be used strictly.

You have to decide. Where what should be used. __stdcall doesn't permit variable number of arguments hence which calling convention will you use?

Meat Loaf wrote:

Thiscall calling convention is the default calling convention used by C++ member functions that do not use variable arguments.

This calling convention allows class member functions to have the implicit this argument.

Meat Loaf wrote:

(yes, I've not gone through the article fully

Then please do. :)

Nibu thomas A Developer Programming tips[^]

User 3037427

Thanks for ur reply.:)