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 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 |
| thiscall (not a keyword) |
Callee | Pushed on stack; this pointer stored in ECX |
For related information, see Obsolete Calling Conventions.