KB100832 - Description of the calling conventions that the 32-bit compiler supports

SUMMARY

Visual C++, 32-bit Edition, supports three calling conventions: C (_cdecl), standard (_stdcall), and fastcall (_fastcall). The compiler does not support the Pascal calling convention (_pascal) provided by Microsoft compilers for MS-DOS and 16-bit Windows.

The following table summarizes the calling conventions.

                          _cdecl         _stdcall       _fastcall

   -------------------------------------------------------------------
   Arguments              Pushed R to L  Pushed R to L  Note 3
   Stack cleaned up by    Caller         Called         Called
   Naming convention      Prepend "_"    Note 1         Note 2

Note 1 The _stdcall calling convention decorates each function name by prepending an underscore character (as the _cdecl convention does) and appending an at sign "@" and the decimal representation of the number of bytes of stack space required. Each argument is widened to a multiple of four bytes.

Note 2 The _fastcall calling convention decorates each function name by prepending an at sign "@" and appending an at sign and the decimal representation of the number of bytes of stack space required. Each argument is widened to a multiple of four bytes.

Note 3 The first two function arguments that require four or fewer bytes are placed into registers. The caller pushes the remainder of the parameters onto the stack from right to left. This behavior may change in future versions.

The default calling convention is _cdecl. If an application declares a function that accepts a variable number of arguments with the _fastcall or _stdcall calling convention, the compiler uses the _cdecl calling convention for that function.

MORE INFORMATION

int _cdecl CFunc(int a, int b); calling function called function ------------------------------------------- push b _CFunc PROC NEAR push a . call _CFunc . add esp,8 . . RET . _CFunc ENDP . int _cdecl CVarFunc(int a, ...); calling function called function ------------------------------------------- push ... _CVarFunc PROC NEAR push a . call _CVarFunc . add esp,4+... . . RET . _CVarFunc ENDP .

int _stdcall StdFunc(int a, int b); calling function called function ------------------------------------------- push b _StdFunc@8 PROC NEAR push a . call _StdFunc@8 . . . . RET 8 . _StdFunc@8 ENDP

int _fastcall FastFunc(int a, int b); calling function called function ------------------------------------------- mov edx, b @FastFunc@8 PROC NEAR mov ecx, a . call @FastFunc@8 . . . . RET 8 . @FastFunc@8 ENDP