Argument Passing and Naming Conventions

Microsoft Specific

All arguments are widened to 32 bits when they are passed. Return values are also widened to 32 bits and returned in the EAX register, except for 8-byte structures, which are returned in the EDX:EAX register pair. Larger structures are returned in the EAX register as pointers to hidden return structures. Parameters are pushed onto the stack from right to left. Structures that are not PODs will not be returned in registers.

The compiler generates prolog and epilog code to save and restore the ESI, EDI, EBX, and EBP registers, if they are used in the function.

Nota

When a struct, union, or class is returned from a function by value, all definitions of the type need to be the same, else the program may fail at runtime.

For information on how to define your own function prolog and epilog code, see Naked Function Calls.

The following calling conventions are supported by the Visual C/C++ compiler.

Keyword	Stack cleanup	Parameter passing
__cdecl	Caller	Pushes parameters on the stack, in reverse order (right to left)
__clrcall	n/a	Load parameters onto CLR expression stack in order (left to right).
__stdcall	Callee	Pushes parameters on the stack, in reverse order (right to left)
__fastcall	Callee	Stored in registers, then pushed on stack
__thiscall	Callee	Pushed on stack; this pointer stored in ECX

For related information, see Obsolete Calling Conventions.

END Specific

See Also

Concepts

Calling Conventions