This documentation is archived and is not being maintained.

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.

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.

Note   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)
__stdcall Callee Pushes parameters on the stack, in reverse order (right to left)
__fastcall Callee Stored in registers, then pushed on stack
(not a keyword)
Callee Pushed on stack; this pointer stored in ECX

For related information, see Obsolete Calling Conventions.

END Microsoft Specific

See Also

Calling Conventions