Article: Q117428
Product(s): Microsoft C Compiler
Version(s): 1.0,2.0,2.1,4.0,5.0,6.0
Operating System(s):
Keyword(s): kbLangCPP kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600
Last Modified: 11-FEB-2002
-------------------------------------------------------------------------------
The information in this article applies to:
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 5.0, 6.0
-------------------------------------------------------------------------------
SUMMARY
=======
When porting code that uses GetProcAddress() from C to C++, the C++ compiler for
MS-DOS can return the following error message:
error C2564: formal/actual parameters mismatch in call through pointer to
function
The error message that is returned with the 32-bit compiler is:
error C2197: 'int (__stdcall *)(void )' : too many actual parameters
MORE INFORMATION
================
In a traditional C application, use GetProcAddress() to obtain the address of a
function to be called. Declare a variable of type FARPROC, initialize the
pointer with the value returned from GetProcAddress(), and then call the
function through a pointer as shown:
void func1(void)
{
HINSTANCE hLib;
FARPROC lpfnDLLProc;
UINT param1 = 1;
int param2;
hLib = LoadLibrary ("dll1.dll");
if (hLib)
{
lpfnDLLProc = GetProcAddress (hLib, "DLLProc");
(*lpfnDLLProc) (param1, (LPINT)¶m2);
FreeLibrary (hLib);
}
}
When not compiling with STRICT, FARPROC is defined in the WINDOWS.H file as
follows:
typedef int (CALLBACK* FARPROC)();
When the sample code above is converted to C++, a type-mismatch error occurs
because C and C++ have a fundamental difference in the way they interpret empty
parentheses in function declarations. In C, a function declared as follows:
int (*funcptr)();
declares a function that accepts an unknown number of arguments. In C++, the same
declaration represents a function that accepts no arguments. In other words, in
C++, the statement is equivalent to:
int (*funcptr)(void);
Because of this difference, when a pointer of type FARPROC is used to call a
function with parameters in C, no error occurs. In C++, when the function being
passed to GetProcAddress() has parameters, the formal/actual-parameter-mismatch
error occurs because the function of type FARPROC is defined as a function that
has void parameters rather than as a function that accepts parameters.
To eliminate the error, define the function pointer as a pointer to a function
with the correct number of parameters and then typecast the return value from
GetProcAddress() to the appropriate type:
typedef void (CALLBACK *ULPRET)(UINT,LPINT);
void func1(void)
{
HINSTANCE hLib;
ULPRET lpfnDLLProc;
UINT param1 = 1;
int param2;
hLib = LoadLibrary ("dll1.dll");
if (hLib)
{
lpfnDLLProc = (ULPRET) GetProcAddress (hLib,"DLLProc");
(*lpfnDLLProc) (param1, (LPINT)¶m2);
FreeLibrary (hLib);
}
}
Additional query words: 8.00 8.00c 9.00 9.10
======================================================================
Keywords : kbLangCPP kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600
Technology : kbVCsearch kbVC400 kbAudDeveloper kbvc100 kbVC500 kbVC600 kbVC200 kbVC210 kbVC32bitSearch kbVC500Search
Version : :1.0,2.0,2.1,4.0,5.0,6.0
Issue type : kbinfo
=============================================================================