Why won't std::shared_ptr accept my deleter function object? - c++

I'm have a problem with *passing a deleter functor into a std::smart_ptr*. This is the first time I've tried anything like this, so I may be overlooking something very simple..
Here's what my functor class looks like;
#pragma once;
#ifndef ASSETDELETERS_H
#define ASSETDELETERS_H
#include "RenderSystem.h"
struct SourceImageDeleter
{
RenderSystem & refGraphicsRenderer;
unsigned int * ptrTextureID;
explicit SourceImageDeleter( RenderSystem & tempRef, unsigned int * tempPtrID )
: refGraphicsRenderer( tempRef ) ,
ptrTextureID(tempPtrID) {};
SourceImageDeleter( const SourceImageDeleter & originalCopy )
: refGraphicsRenderer( originalCopy.refGraphicsRenderer ) ,
ptrTextureID( originalCopy.ptrTextureID ) {};
void operator() ()
{
refGraphicsRenderer.deregisterTexture( ptrTextureID );
}
};
#endif
The RenderSystem::deregisterTexture function only requires one argument (unsigned int *), because of that, it's being passed at the creation of the functor. I've looked into the use of std::bind, but I don't have much experience with that and wasn't able to have much success using it instead of making a functor.
And here's the only method that uses it so far..
std::shared_ptr<SourceImage> Engine::createSourceImage( std::string tempFilepath )
{
SourceImage * tempImagePtr = new SourceImage( tempFilepath );
registerTexture( &tempImagePtr->textureID, &tempImagePtr->image );
return std::shared_ptr<SourceImage>( tempImagePtr , SourceImageDeleter( this->graphicsRenderer, &tempImagePtr->textureID ) );
}
I'm not sure why it's not working! I've basically been trying to have my smart_ptr run a custom deletion function all week, and between trying to figure out how pointers-to-method passing works, how std::bind/std::mem_fun_ref works, and how functors work has been stumping me all week..
Anyway, here's the compile error that Visual Studio has been giving me, I hope someone can help me figure out what I've been screwing up;
error C2064: term does not evaluate to a function taking 1 arguments
1> class does not define an 'operator()' or a user defined conversion operator to a pointer-to-function or reference-to-function that takes appropriate number of arguments
1> c:\program files (x86)\microsoft visual studio 10.0\vc\include\memory(1438) : see reference to function template instantiation 'void std::tr1::shared_ptr<_Ty>::_Resetp<_Ux,_Dx>(_Ux *,_Dx)' being compiled
1> with
1> [
1> _Ty=SourceImage,
1> _Ux=SourceImage,
1> _Dx=SourceImageDeleter
1> ]
1> c:\projects\source\engine.cpp(151) : see reference to function template instantiation 'std::tr1::shared_ptr<_Ty>::shared_ptr<SourceImage,SourceImageDeleter>(_Ux *,_Dx)' being compiled
1> with
1> [
1> _Ty=SourceImage,
1> _Ux=SourceImage,
1> _Dx=SourceImageDeleter
1> ]
(By the way, engine.cpp(151) is the return line inside Engine::createSourceImage shown above.. If I remove the deleter argument, the program compiles and runs fine aside from the obvious resource leaks associated with improper image deletion..)

std::shared_ptr passes in the pointer being deleted to the deleter, which is exactly what your error message says: the class does not define an operator() with the correct number of arguments.
Your deleter isn't expecting any parameters, so it won't work; you'll need to change it to void operator()(SourceImage*)

Related

std::function vs alias function pointer , why one wont compile

Wanting to investigate the performance hit (if any) of std:function.
I have this struct:
struct InstructionDescription
{
std::string name;
word mask;
word code;
std::function<void(Cpu*, word)> func;
word flags;
};
and I set up a vector of them like this
std::vector<InstructionDescription> instructions_{
{
{"clr", DD_MASK, 0005000, &Cpu::Clr},
{"clrb", DD_MASK, 0105000, &Cpu::Clr},
{"com", DD_MASK, 0005100, &Cpu::Com},
.....
Works fine. Now if I change the struct to use a function pointer:
using InstrFunc = void(*)(Cpu*, word);
struct InstructionDescription
{
std::string name;
word mask;
word code;
InstrFunc func;
word flags;
};
which as far as I can see should be equivalent. And yet I get
1>C:\work\pdp\mysim\mysim\instructions.h(60,50): error C2664: 'std::vector<Cpu::InstructionDescription,std::allocator<Cpu::InstructionDescription>>::vector(std::initializer_list<_Ty>,const _Alloc &)': cannot convert argument 1 from 'initializer list' to 'std::initializer_list<_Ty>'
1> with
1> [
1> _Ty=Cpu::InstructionDescription,
1> _Alloc=std::allocator<Cpu::InstructionDescription>
1> ]
1> and
1> [
1> _Ty=Cpu::InstructionDescription
1> ]
1>C:\work\pdp\mysim\mysim\instructions.h(60,50): message : Element '1': no conversion from 'initializer list' to '_Ty'
1> with
1> [
1> _Ty=Cpu::InstructionDescription
1> ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.25.28610\include\vector(512,5): message : see declaration of 'std::vector<Cpu::InstructionDescription,std::allocator<Cpu::InstructionDescription>>::vector'
1>Console.cpp
VS2019. VS GUI is also highlighting the std::vector line saying 'InstructionDescription' is unknown and that the function names are not accessible (&Cpu::Clr for example)
The Cpu class is defined like:
struct Cpu {
void Clr(word) {};
void Com(word) {};
};
What am I doing wrong?
The std::function is very convenient: it recognizes that &Cpu::Clr is a member function whose first parameter will be a Cpu*.
When you make it a function pointer, this doesn't work like this. You have to use a member function pointer:
using InstrFunc = void (Cpu::*)(word);
Additional info
This is standard: std::function nicely copes with pointers to member functions by adding a pointer to the class as first argument. Of course, when you call it, you have to provide that additional parameter:
Cpu cpu;
for (auto& i:instructions_) {
i.func(&cpu, i.code); // as simple as that with std::function
}
When you go for the pointer to member function, it's less convenient:
Cpu cpu;
for (auto& i:instructions) {
(cpu.*i.func)(i.code);
}
Online demo (you need to comment/ comment out the specific lines)

How can I initialize the default value of a CArray<CClass*> function parameter with an empty CArray?

I know I could do this better with std::vector, but the application I am messing with, has already a bunch of CArray parameters on a lot of related functions ... and I will not change them all at the moment!
I simply want to define an empty CArray<CClass*> — array of pointers to CClass, so the problem can not be on the CClass constructor — as the default value of a function parameter.
Approach 1
If I try to do it with assignment operator and default constructor:
void Function(CArray<CClass*> parameter = CArray<CClass*>());
I get the error:
1>C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\atlmfc\include\afxTempl.h(262): error C2248: 'CObject::CObject' : cannot access private member declared in class 'CObject'
1> C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\atlmfc\include\afx.h(535) : see declaration of 'CObject::CObject'
1> C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\atlmfc\include\afx.h(510) : see declaration of 'CObject'
1> This diagnostic occurred in the compiler generated function 'CArray<TYPE>::CArray(const CArray<TYPE> &)'
1> with
1> [
1> TYPE=CClass *
1> ]
Approach 2
I also tried with a copy constructor:
void Function(CArray<Class*> parameter(CArray<CClass*>()));
I got the errors:
>File.cpp(line X): error C2664: 'FunctionClass::Function' : cannot convert parameter 1 from 'CArray<TYPE>' to 'CArray<TYPE> (__cdecl *)(CArray<TYPE> (__cdecl *)(void))'
1> with
1> [
1> TYPE=CClass*
1> ]
1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
line X: contains a call supplying the parameter to Function, as shown: pFunctionClass->Function(parameter);
1>CFunctionClass.cpp(line Y): error C2511: 'void CFunctionClass::Function(CArray)' : overloaded member function not found in 'CShoePlaceDoc'
1> with
1> [
1> TYPE=CClass*
1> ]
1> FunctionClass.h(line A) : see declaration of 'CFunctionClass'
line Y contains the Function implementation header, as shown: `void CFunctionClass::Function(CArray parameter)
1>File.cpp(line Z): error C2660: 'CClassFunction::Function' : function does not take 0 arguments
line Z: contains a call to Functionwithout supplying it parameters, as shown: pClassFunction->Function();
The approach didn't work, but it got its way towards a conclusion: It is not possible to use a copy-constructor for assigning a default value for a function parameter.
Approach 3
And if I try with a lambda:
void Function(CArray<CClass*> parameter = [] () -> CArray<CClass*>{ return CArray<CClass*> (); } );
, then I will get multiple outputs of these two errors:
1>FunctionClass.h(line A): error C2440: 'default argument' : cannot convert from '`anonymous-namespace'::<lambda2>' to 'CArray<TYPE>'
1> with
1> [
1> TYPE=CClass*
1> ]
1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>FunctionClass.h(line B): fatal error C1903: unable to recover from previous error(s); stopping compilation
line A: method declaration
line B: closing } of FunctionClass class that contains Function method
Origin of the problem
The root cause of the problem seems to be the fact that CArray is a class directly derived from CObject, which declares the assignment operator as private:
class AFX_NOVTABLE CObject
{
//...
private:
CObject(const CObject& objectSrc); // no implementation
void operator=(const CObject& objectSrc); // no implementation
//...
}
So, how can I supply an empty array as default value for the parameter?
With this declaration
void Function(CArray<CClass*> parameter /*...*/);
You can't. Calling this function will invoke the private copy constructor of CObject as you have noticed.
What you could do, is to add a object of static CArray<CClass*> in your class and initialize the function with a reference to it. This way it will be empty (as long as you do not populate it...) and you can perform a .IsEmpty() check on it.
private:
static CArray<CClass*> myObj;
//...
void Function(CArray<CClass*> &parameter = myObj);
Or initialize it to 0. This way you simply check it by if (parameter) or if (NULL == parameter).
void Function(CArray<CClass*> *parameter = NULL);

Visual C++ Can't Properly fill Constructor Requirements

So I can't seem to properly fill the requirements for this constructor.
DIVA_STATUS DIVA_getObjectDetailsList (
IN BOOL pFirstTime,
IN time_t *initialTime,
IN int pListType,
IN int pObjectsListType,
IN int pMaxListSize,
IN DIVA_STRING pObjectName,
IN DIVA_STRING pObjectCategory
IN DIVA_STRING pMediaName
DIVA_LEVEL_OF_DETAIL pLevelOfDetail,
IN vector<DIVA_STRING> listPosition,
OUT vector<DIVA_OBJECT_DETAILS_LIST> *&pObjectDetailsList
)
The problem seems to be the last line which outputs a vector of classes (???). I'm a little rusty with C++ so I cant recall why you would dereference a reference call (*&).
DIVA_OBJECT_DETAILS_LIST is a class shown below:
class DIVA_OBJECT_DETAILS_LIST {
public:
int listType;
DIVA_STRING siteID;
vector<DIVA_STRING> *listPosition;
vector<DIVA_OBJECT_INFO> *objectInfo;
vector<DIVA_OBJECT_TAPE_INFO> *objectTapeInfo;
};
Here is what I get when I try compiling using VC++ 2008 Express
1>Compiling...
1>initiator.cpp
1>.\initiator.cpp(148) : error C2100: illegal indirection
1>.\initiator.cpp(148) : error C2665: 'DIVA_getObjectDetailsList' : none of the 2 overloads could convert all the argument types
1> z:\Mediavault1\Automation\DIVA_API\DIVArchiveAPI\CppAPI Test\include\DIVAapi.h(2191): could be 'DIVA_STATUS DIVA_getObjectDetailsList(bool,time_t,int,int,int,DIVA_STRING,DIVA_STRING,DIVA_STRING,DIVA_LEVEL_OF_DETAIL,std::vector<_Ty>,DIVA_OBJECT_DETAILS_LIST *&)'
1> with
1> [
1> _Ty=DIVA_STRING
1> ]
1> while trying to match the argument list '(bool, time_t, int, int, int, DIVA_STRING, DIVA_STRING, DIVA_STRING, DIVA_LEVEL_OF_DETAIL, std::vector<_Ty>, DIVA_OBJECT_DETAILS_LIST *)'
1> with
1> [
1> _Ty=DIVA_STRING
1> ]
Here is how I'm calling the constructor:
cr = DIVA_getObjectDetailsList (
_firstTime,
(time_t)_initDate,
(int)DIVA_OBJECTS_LIST,
(int)DIVA_OBJECTS_CREATED_SINCE,
_size,
_name,
_category,
_group,
DIVA_INSTANCE,
*_listType.listPosition,
&*_listType
);
_listType is DIVA_OBJECT_DETAILS_LIST. How do I pass it pointer by reference?
The problem appears to be with the second to last argument. You are passing a std::vector<DIVA_STRING>* when you should just be passing a std::vector<DIVA_STRING> (not a pointer).
But to help your understanding about the last argument, vector<DIVA_OBJECT_DETAILS_LIST>*& is a "reference to pointer to vector<DIVA_OBJECT_DETAILS_LIST>" type. That is, you should pass a pointer and it is passed by reference.

What is this compiler error when using a lambda as a template parameter?

Edit:
This has been reported as a VS2012 C++ compiler bug on Microsoft Connect (link).
Nov. 11, 2014: Microsoft has responded saying the fix for this bug should show up in the next major release of Visual C++.
I've been struggling with a VS2012 compiler error message I don't understand, so I trimmed down the problem to what seems like the bare minimum.
I'm building the following main.cpp using VS2012:
#include <utility>
template <typename T>
struct A
{
T x;
A(A&& other) : x(std::move(other.x)) { }
A(T&& x) : x(std::move(x)) { }
};
template <typename T>
A<T> build(T&& x)
{
return A<T>(std::move(x));
}
int main(int argc, char* argv[])
{
auto f = []()
{
return build([](){}); //error here
};
return 0;
}
The salient point is that I'm trying to use a lambda as the template type T of the build function. The error message I get is:
1> main.cpp
1>C:\test\main.cpp(21): error C2664: 'A<T>::A(A<T> &&)' : cannot convert parameter 1 from 'A<T>' to 'A<T> &&'
1> with
1> [
1> T=void (__cdecl *)(void)
1> ]
1> and
1> [
1> T=main::<lambda_c3c618d445b3cb24eede9bf304860ad7>::()::<lambda_4240e93016e3e420ff8383c9350ae130>
1> ]
1> and
1> [
1> T=void (__cdecl *)(void)
1> ]
1> Reason: cannot convert from 'A<T>' to 'A<T>'
1> with
1> [
1> T=main::<lambda_c3c618d445b3cb24eede9bf304860ad7>::()::<lambda_4240e93016e3e420ff8383c9350ae130>
1> ]
1> and
1> [
1> T=void (__cdecl *)(void)
1> ]
1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
I've done my research and looked up the page for the error message (link), but I still can't figure out what the problem is. Could you please explain this compiler error?
edit
Something is definitely weird here. If I change the code in main to look like this:
auto f = []()
{
int* n = new int(0);
auto g = [=](){ return *n; };
*n++;
return build<decltype(g)>(std::move(g));
};
I get an error message suggesting that T=int (__cdecl *)(void) in the call to build - which would mean that decltype(g) is giving me a function pointer? Huh? I'm capturing a pointer by value and then modifying it afterwards - shouldn't it have to create a functor - and one that has no cast to function pointer? Maybe I'm not understanding something.
See related: Lambda expressions : n3290 draft
Also, if this is a bug in the VS2012 compiler, can you think of a workaround?
I can confirm that using GCC (on linux), this code compiles just fine.
So I'd say that VisualStudio seems to be the source of the error.
I don't have Windows or Visual Studio to verify, nor do I have much experience with lambda functions in C++, but perhaps you need to include the (albeit empty) parameter list in the function? i.e. change line 21 to
return build([](){});
Both versions compile with GCC, but perhaps Visual Studio is a bit more picky.
The other question I might have is whether the lambda function you're defining at line 24 will work out since its return value involves the lambda function you're defining inside the function itself.
I do not know if that behavior comply with the standard but with VC++ 2019 that error happen only with the option /permissive-, then when the strict mode is on.
Nevertheless here is how to solve the problem, by just casting the lambda with a reference type:
template <typename FUNC>
void f(FUNC& o){}
int main()
{
f((std::function<void()>&)[](){});
// or also:
auto func = [](){};
f(func);
}

std::vector - error: cannot delete objects that are not pointers

Maybe someone can help me understand the error.
I write this code:
class Text
{
private:
struct paragraph
{
vector<string> lines;
};
vector<shared_ptr<paragraph>> paragraphs;
public:
Text()
{
paragraphs.push_back(shared_ptr<paragraph>(new paragraph()));
}
};
int main()
{
shared_ptr<Text> pText(nullptr);
Text text();
pText.reset(&text);
return 0;
}
When I try to run it
I got this error:
1>c:\program files\microsoft visual studio 10.0\vc\include\memory(1664): error C2541: 'delete' : cannot delete objects that are not pointers
1> c:\program files\microsoft visual studio 10.0\vc\include\memory(1431) : see reference to function template instantiation 'void std::tr1::shared_ptr<_Ty>::_Resetp<_Ux>(_Ux (__cdecl *))' being compiled
1> with
1> [
1> _Ty=Text,
1> _Ux=Text (void)
1> ]
1> c:\program files\microsoft visual studio 10.0\vc\include\memory(1607) : see reference to function template instantiation 'std::tr1::shared_ptr<_Ty>::shared_ptr<_Ux>(_Ux (__cdecl *))' being compiled
1> with
1> [
1> _Ty=Text,
1> _Ux=Text (void)
1> ]
1> c:\documents and settings\owner\שולחן העבודה\e\class.cpp(29) : see reference to function template instantiation 'void std::tr1::shared_ptr<_Ty>::reset<Text(void)>(_Ux (__cdecl *))' being compiled
1> with
1> [
1> _Ty=Text,
1> _Ux=Text (void)
1> ]
What is meant "cannot delete objects that are not pointers"?
I'm not trying to delete any object.
In addition to the most vexing parse, your code contains a fundamental flaw:
You must not assign a pointer to a stack-allocated object to a shared_ptr.
This code will cause undefined behaviour which in practice means lots of pain:
shared_ptr<Text> pText(nullptr);
Text text;
pText.reset(&text);
shared_ptr will try to delete &text at the end of its lifetime.
The line Text text(); does not do what you think it does.
It parses it as the declaration of a function named text which accepts no argument and returns a value of type Text.
This is the reason why your line pText.reset(&text); does not compile.
However, you really do not want that line to compile: you are associating a shared_ptr object to a value with automatic storage duration: when the shared_ptr will go out of scope, it will try to delete that object, resulting in Undefined Behavior (most likely a crash in this case).
You main function should read.
int main()
{
shared_ptr<Text> pText(new Text);
return 0;
}
You had 2 problems. First, Text text() was being parsed as a function declaration. Second, you were passing the address of a stack variable to a shared_ptr, which will delete the object when the reference count reaches 0.
You should also consider whether you need to use a shared_ptr. Will you ever be sharing this pointer with any body else, or do you simply want to ensure it is destructed properly? You could consider unique_ptr in the latter case. Do you even need a pointer at all, could you just allocate the object on the stack?