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Microsoft Specific

This is the default calling convention for C and C++ programs. Because the stack is cleaned up by the caller, it can do vararg functions. The __cdecl calling convention creates larger executables than __stdcall, because it requires each function call to include stack cleanup code. The following list shows the implementation of this calling convention.

Element Implementation

Argument-passing order

Right to left

Stack-maintenance responsibility

Calling function pops the arguments from the stack

Name-decoration convention

Underscore character (_) is prefixed to names, except when exporting __cdecl functions that use C linkage.

Case-translation convention

No case translation performed


For related information, see Decorated Names.

On Itanium Processor Family (IPF) and x64 processors, __cdecl is accepted and ignored by the compiler; on IPF, by convention, parameters are passed in register.

Place the __cdecl modifier before a variable or a function name. Because the C naming and calling conventions are the default, the only time you need to use __cdecl is when you have specified the /Gz (stdcall) or /Gr (fastcall) compiler option. The /Gd compiler option forces the __cdecl calling convention.

For non-static class functions, if the function is defined out-of-line, the calling convention modifier does not have to be specified on the out-of-line definition. That is, for class non-static member methods, the calling convention specified during declaration is assumed at the point of definition. Given this class definition,

struct CMyClass {
   void __cdecl mymethod();


void CMyClass::mymethod() { return; }

is equivalent to this

void __cdecl CMyClass::mymethod() { return; }

In the following example, the compiler is instructed to use C naming and calling conventions for the system function:

// Example of the __cdecl keyword on function
int __cdecl system(const char *);
// Example of the __cdecl keyword on function pointer
typedef BOOL (__cdecl *funcname_ptr)(void * arg1, const char * arg2, DWORD flags, ...);
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