__stdcall

Microsoft Specific

The __stdcall calling convention is used to call Win32 API functions. The callee cleans the stack, so the compiler makes vararg functions __cdecl. Functions that use this calling convention require a function prototype.

Syntax

return-type __stdcall function-name[( argument-list )]

Remarks

The following list shows the implementation of this calling convention.

Element Implementation
Argument-passing order Right to left.
Argument-passing convention By value, unless a pointer or reference type is passed.
Stack-maintenance responsibility Called function pops its own arguments from the stack.
Name-decoration convention An underscore (_) is prefixed to the name. The name is followed by the at sign (@) followed by the number of bytes (in decimal) in the argument list. Therefore, the function declared as int func( int a, double b ) is decorated as follows: _func@12
Case-translation convention None

The /Gz compiler option specifies __stdcall for all functions not explicitly declared with a different calling convention.

For compatibility with previous versions, _stdcall is a synonym for __stdcall unless compiler option /Za (Disable language extensions) is specified.

Functions declared using the __stdcall modifier return values the same way as functions declared using __cdecl.

On ARM and x64 processors, __stdcall is accepted and ignored by the compiler; on ARM and x64 architectures, by convention, arguments are passed in registers when possible, and subsequent arguments are passed on the stack.

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 __stdcall mymethod();
};

this

void CMyClass::mymethod() { return; }

is equivalent to this

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

Example

In the following example, use of __stdcall results in all WINAPI function types being handled as a standard call:

// Example of the __stdcall keyword
#define WINAPI __stdcall
// Example of the __stdcall keyword on function pointer
typedef BOOL (__stdcall *funcname_ptr)(void * arg1, const char * arg2, DWORD flags, ...);

See also

Argument Passing and Naming Conventions
Keywords