ChangeServiceConfig2 using GetProcAddress to support multiple version of windows - c++

Question

I'm using ChangeServiceConfig2 API of windows to change the service description. Since the same api is not supported in windows 98, ME I have used LoadLibraray and GetProcAddress to prevent static linking of the API in the exe. Please refer the code for more details:
typedef BOOL (*ChgSvcDesc) (SC_HANDLE hService, DWORD dwInfoLevel, LPVOID lpInfo);
eBool ServiceConfigNT::Install(IN tServiceDesc * pServiceDesc){
SC_HANDLE hservice;
SC_HANDLE hservicemgr;
SERVICE_DESCRIPTION desc;
ULong starttype;
HMODULE hmod;
ChgSvcDesc fpsvcdesc;
// Opens the Service Control Manager
hservicemgr = OpenSCManager(NULL, NULL, SC_MANAGER_ALL_ACCESS);
if(!hservicemgr){
vPrepareError(_TEXT("Failed to open service control manager!!"));
goto err;
}
// Set start method of service.
starttype = (pServiceDesc->uAutoStart == TRUE)? SERVICE_AUTO_START : SERVICE_DEMAND_START;
// Create the service
hservice = CreateService(hservicemgr, vServiceName, pServiceDesc->uDisplayName, SERVICE_ALL_ACCESS,
pServiceDesc->uServiceType, starttype, SERVICE_ERROR_NORMAL,pServiceDesc->uExePath,
NULL, NULL, NULL, NULL, NULL);
if(!hservice) {
vPrepareError(_TEXT("Failed to create service.!!"));
goto err;
}
// Set the description string
if(pServiceDesc->uServiceDescription && *pServiceDesc->uServiceDescription) {
desc.lpDescription = pServiceDesc->uServiceDescription;
// This cannot be executed since it is not supported in Win98 and ME OS
//(Void)ChangeServiceConfig2 (hservice, SERVICE_CONFIG_DESCRIPTION, &desc);
hmod = LoadLibrary(_TEXT("Advapi32.dll"));
if(hmod) {
// _UNICODE macro is set, hence im using the "W" version of the api
fpsvcdesc = (ChgSvcDesc)GetProcAddress(hmod, "ChangeServiceConfig2W");
if(fpsvcdesc)
// On execution of the below statement, I get the error handle is invalid
fpsvcdesc(hservice, SERVICE_CONFIG_DESCRIPTION, &desc);
}
CloseServiceHandle(hservice);
CloseServiceHandle(hservicemgr);
return TRUE;
err:
if(hservicemgr)
CloseServiceHandle(hservicemgr);
return FALSE;
}
I debugged the code many times to find out why I am getting handle is invalid error ? On calling the API directly the description of service is changing but using the function pointer it gives the error.
I think that the API is writing something to the service handle of the SCM, but I have no clues as to why ?
Can somebody help me with this ?

Answer 1

Your function pointer is declared with no calling convention specified. The default calling convention is __cdecl. But Windows API functions are __stdcall. You need to add the calling convention to your function pointer type.
typedef BOOL (__stdcall *ChgSvcDesc) (SC_HANDLE hService,
DWORD dwInfoLevel, LPVOID lpInfo);