Program crashed when assigning value to a structure field

Question

I am learning C++, recently I encountered a problem and don't know why.

I want to hide the private member fields details from outside users, so I just declare a void* pointer as the only one private member field, and then declare the real member fields structure in class' .cpp source file. new this inner hidden structure in class constructor, and delete it in class destructor.

Below is my test codes:

ItemA.h

#pragma once

class ItemA
{
private:
    void* pFields;

public:
    ItemA();
    ~ItemA();
};

ItemA.cpp

#include "ItemA.h"
#include <string>

using namespace std;

typedef struct
{
    int    intField;
    string strField;
} HFIELDS, *PHFIELDS;

ItemA::ItemA()
{
    this->pFields = new HFIELDS;
    PHFIELDS pHFIELDS = (PHFIELDS)this->pFields;
    pHFIELDS->intField = 100;
    pHFIELDS->strField = "100";
}

ItemA::~ItemA()
{
    PHFIELDS pHFIELDS = (PHFIELDS)this->pFields;
    delete pHFIELDS;
}

ItemB.h

#pragma once

#include "ItemA.h"

class ItemB
{
private:
    void* pFields;
    ItemB();

public:
    ItemB(ItemA &itemA);
    ~ItemB();
};

ItemB.cpp

#include "ItemB.h"
#include <string>

using namespace std;

typedef struct
{
    ItemA* pItemA;
    int    intField;
    string strField;
} HFIELDS, *PHFIELDS;

ItemB::ItemB(ItemA &itemA)
{
    this->pFields = new HFIELDS;
    PHFIELDS pHFIELDS = (PHFIELDS)(this->pFields);
    pHFIELDS->pItemA = &itemA;
    pHFIELDS->intField = 200;
    pHFIELDS->strField = "200";
}


ItemB::~ItemB()
{
    PHFIELDS pHFIELDS = (PHFIELDS)this->pFields;
    delete pHFIELDS;
}

main.cpp

#include <tchar.h>
#include "ItemA.h"
#include "ItemB.h"

int _tmain(int argc, _TCHAR* argv[])
{
    ItemA* pItemA = new ItemA();
    ItemB* pItemB = new ItemB(*pItemA);
    delete pItemB;
    delete pItemA;

    return 0;
}

When program execution ran to ItemB's constructor this line it crashed:

pHFIELDS->strField = "200";

Could somebody tell me what's wrong with it? Thank you.

P.S. The development environment I use is MSVC2013.

Why would you use a void pointer for this? You might read about the pimpl idiom: http://stackoverflow.com/questions/60570/why-should-the-pimpl-idiom-be-used — Retired Ninja, Dec 28 '14 at 08:43
Compile with all warnings and debug info (with [GCC](http://gcc.gnu.org/) it means `gcc -Wall -Wextra -g`). Then **use the debugger** (e.g. `gdb`) — Basile Starynkevitch, Dec 28 '14 at 09:07
You could just declare the `private:` field `class Hstruct *pfield;` *without* defining `class Hstruct` in `ItemA.h` — Basile Starynkevitch, Dec 28 '14 at 09:10
Thanks, Basile. One more lesson learned. I will follow the PIMPL idiom. — J.K. Lau, Dec 28 '14 at 09:25

score 3 · Accepted Answer · answered Dec 28 '14 at 08:38

3

why do you have 2 declarations of HFIELDS and *PHFIELDS

1) In ItemA.cpp

typedef struct
{
    int    intField;
    string strField;
} HFIELDS, *PHFIELDS;

2) In ItemB.cpp

typedef struct
{
    ItemA* pItemA;
    int    intField;
    string strField;
} HFIELDS, *PHFIELDS;

What happens is, ItemA.h is included in ItemB so the compiler sees 2 declarations.

Please change name and compile.

Hope this helps.

answered Dec 28 '14 at 08:38

Ganesh Kamath - 'Code Frenzy'

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Thank you Ganesh, your answer helps me. But another question comes, the two structure declarations are in separate cpp files, if this is redefinition problem, why the compiler didn't give me a error or warning? – J.K. Lau Dec 28 '14 at 09:00
separately, this code would have worked for you. when the compiler looks at the same variable name reprezenting 2 different things, it will not be able to resolve. – Ganesh Kamath - 'Code Frenzy' Dec 28 '14 at 09:09
i copied all your code into one file to check if it works. That was when my compiler threw me an error saying there is re-declaration. – Ganesh Kamath - 'Code Frenzy' Dec 28 '14 at 09:12
I am suspecting that some resolutions can be postponed up to run time. Which might have happend in your case. But i am no expert :) – Ganesh Kamath - 'Code Frenzy' Dec 28 '14 at 09:15