Help!!! --- "Expression: _CrtIsValidHeapPointer(pUserData)"

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Hi, guys:

What's wrong with this picture -- -- "Expression: _CrtIsValidHeapPointer(pUserData)".

The exception was caught when I was debugging in a class, codes like below:

class Myclass
{
   Myclass(){
   m_data = new char[50];
   m_data = "You are someone!!";
   }
   ~Myclass(){delete []m_data;}
   
   void SetStr(char *para)
   {
        (NULL == para)
            return;
        if(m_data != para)
        {
            delete []m_data; // The exception was caught here, debugging stopped.
            m_data = NULL;
            m_data = new char[strlen(para)+1];
            strcpy(m_data,para);
        }

   }
private:
   char *m_data;
}



int main(int argc, char* argv[])
{
   Myclass *pMyclass = new Myclass();
   pMyclass->SetStr("Weak !!! ");
   delete  pMyclass;
}

My project was more complicated than what I presented here, but the context about 'm_data' usage was almost the same.

What's the problem while I was trying to release m_data's memory,"delete []m_data", how can I do to avoid?

Posted 19-Mar-11 23:04pm

scu_sundy

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2 solutions

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OriginalGriff · Accepted Answer · 2011-03-19T23:26:00

Solution 1

The first time you go in, the pointer is not to heap memory: it is to static memory!

MIDL

m_data = "You are someone!!";

Posted 19-Mar-11 23:26pm

OriginalGriff

Comments

scu_sundy 20-Mar-11 6:45am

Thanks Griff, you saved me again! my 5

OriginalGriff 20-Mar-11 6:51am

You're welcome!

Sergey Alexandrovich Kryukov 20-Mar-11 21:40pm

Let them reclaim static memory, very useful exercise :-). My 5.
--SA

Emilio Garavaglia · Accepted Answer · 2011-03-20T11:18:00

The way you work with m_data is a nonsense.
Looking the MyClass::MyClass constructor, you first allocate 50 chars from the heap, assigning the address to m_data, then you assign to m_data the address of the literal "You are someone". Since this point, the 50 chars you allocate are leaked (and unreachable) with m_data pointing to a constant literal, that you try do delete later on, in the destructor and in SetStr.

In MyClass::SetStr there is a (NULL==para) return;. It will make more sense if you place an if in front (is it a typo?!?).

In practice, string literal and character arrays don't work the way you think.
In particular

m_data = "You are someone!!";

doesn't copy the string into the array pointed by m_data.

To properly copy you should use library fuctions like strcpy or similar, the does a work like this:

C++

void copy_string(char* dest, unsigned dest_sz, char* src)
{
    unsigned i;
    for(i=0; i<dest_sz-1 && src[i]; ++i)
        dest[i] = src[i];
    dest[i]='\0';
}

Help!!! --- "Expression: _CrtIsValidHeapPointer(pUserData)"

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Help!!! --- "Expression: _CrtIsValidHeapPointer(pUserData)"

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