I am trying to create a function pointer to another function in c++.
This is what I have so far:
LONG (*function)(LPSTR,LPVIPERVAR4,LONG)=&CWilExtender::DllVarHandler;
When I try to compile my program, I get this error:
.\MyExtender.cpp(132) : error C2440: 'initializing' : cannot convert from
'LONG (__thiscall CWilExtender::* )(LPSTR,LPVIPERVAR4,LONG)' to
'LONG (__cdecl *)(LPSTR,LPVIPERVAR4,LONG)'
There is no context in which this conversion is possible
I don't know how the DllVarHandler was defined, and I don't know how to reproduce the type for the function pointer.
How do I change the (_cdecl *) to match (__thisscall CWilExtender::*)?
Specifically, what does LONG (__thiscall CWilExtender::* )(LPSTR,LPVIPERVAR4,LONG) mean and how do I write that as the function pointer's type?
Thanks.
Thanks to the comments by #OliCharlesworth and #user814628, I solved my problem.
The correct code should be:
LONG (CWilExtender::* function)(LPSTR,LPVIPERVAR4,LONG)=&CWilExtender::DllVarHandler;
Thanks for being so quick to help!
Related
In the question How to register member function to lua without lua bind in c++ one answer suggested the following code:
class C {
public:
void blah(lua_State* L);
};
C inst;
lua_pushcclosure(L, std::bind(&C::blah, &inst, std::placeholder::_1), 0);
lua_setglobal(L, "blah");
(Quoted as it stood, including the small error in std::placeholders)
However, I cuold not get that to work. The error message I got back states that the function returned by std::bind can't be converted to a lua_CFunction.
I have also tried changing the return type of blah to int, but I get the same error message. If it's helpful to anyone, the full error message is:
Error C2664 'void lua_pushcclosure(lua_State *,lua_CFunction,int)': cannot convert argument 2 from 'std::_Binder<std::_Unforced,int (__thiscall C::* )(lua_State *),C *,const std::_Ph<1> &>' to 'lua_CFunction'
I even tried to change &C::blah to &inst.blah, but that unsurprisingly didn't work either.
Has anyone gotten it to work? Or is it just not meant to work?
I have some old C++ file which I know used to compile. I have created a new install of Visual C++ version 6.
I am getting lots of compile errors with CStrings about not being able to convert to const char *
Here's an example.
CString dogs = "test";
writeoutfile(dogs, 1);
void Crender::writeoutfile(CString data, long data_size) {}
I get this error:
error C2664: 'void __thiscall Crender::writeoutfile(const char *,long)' : cannot convert parameter 1 from 'class CString' to 'const char *'
Is there some way I can get round this?
You have to get the raw pointer to the char field. This can be done with
CString::GetBuffer()
so you could call
writeoutfile(dogs.GetBuffer(), 1);
CString should convert to const char*. Is it a Unicode build? That's the only explanation I can think of.
GetBuffer() is for getting a writeable pointer to the data contained inside CString. Don't do that!
I've a function declared in this way:
unsigned WINAPI searchSTR(void *j);
And I need a pointer to this function. My idea was:
unsigned (*pointerF) (void*);
pointerF = &searchSTR;
But there is an error:
"1 error C2440: '=' : cannot convert from 'unsigned int (__stdcall *)(void *)'
to 'unsigned int (__cdecl *)(void *)' ".
I tried other sintax, but nothing seems correct, he doesn't like the word WINAPI.
Can you suggest me the correct syntax? Maybe it is easy but I am blocked ! Thanks to all
The WINAPI macro expands to __stdcall, which is a different calling convention from the default __cdecl. You need to mark your function pointer with the calling convention to use:
unsigned (WINAPI *pointerF) (void*)
auto pointerF = &searchSTR;
Stop writing 1990's code. The compiler already knows the right type.
I use Multi-thread method in vs2008 ,use c++ language. when I use _beginthreadex function， I got the follow error:
error C2664: '_beginthreadex' : cannot convert parameter 3 from 'unsigned int
(__stdcall *)(void *)' to 'unsigned int (__stdcall *)(void *)'
ps: I use the template on the threadFunc like this:
template<class T>
unsigned int WINAPI closingReconstruction_ThreadFunc(void* pvPara)
{...}
,and then i creat the thread
_beginthreadex(NULL,0,closingReconstruction_ThreadFunc<T>,(PVOID)(tPara+i),0,NULL)
so i get this error , of course , if I remove the template ,it can be work,but i need to use template, are there any methods to solve this.
You forgot to mention the immediately preceding error message,
error C2065: 'T' : undeclared identifier
Let me just state that looking at the first error message first, is generally a good idea.
Cheers & hth.,
I have a class SoundManager which contains a function called 'recordLoop'. In the constructor of the SoundManager, I am using this code:
recordHandle = (HANDLE)_beginthreadex(NULL,0,recordLoop,
(void*)exinfo->length,CREATE_SUSPENDED,0);
It is giving me the following errors:
error C3867: 'SoundManager::recordLoop': function call missing argument list; use '&SoundManager::recordLoop' to create a pointer to member
IntelliSense: argument of type "unsigned int (__stdcall SoundManager::*)(void *params)" is incompatible with parameter of type "unsigned int (__stdcall *)(void *)"
So I've tried using the &SoundManager::recordLoop as suggested, but it gives me this:
error C2664: '_beginthreadex' : cannot convert parameter 3 from 'unsigned int (__stdcall SoundManager::* )(void *)' to 'unsigned int (__stdcall *)(void *)'
IntelliSense: argument of type "unsigned int (__stdcall SoundManager::*)(void *params)" is incompatible with parameter of type "unsigned int (__stdcall *)(void *)"
Is it illegal to start a thread on a class method or did I do something wrong?
Thanks in advance
EDIT: Sorry forgot to add the recordLoop >.< here it is:
public:
unsigned __stdcall recordLoop(void* params);
It's illegal to start a thread on a non-static class member since there is no way for the created thread to know what this is.
What is the definition of recordLoop?
I had the same problem with casting.
Ignoring all other problems like one mentioned in the answer above, function pointer must be cast to (unsigned(__stdcall*)(void*)) in _beginthreadex, no matter what type the function is or what is its parameter list.