_BLOCK_TYPE_IS_VALID(pHead -> nBlockUse)

This is a discussion on _BLOCK_TYPE_IS_VALID(pHead -> nBlockUse) within the C++ Programming forums, part of the General Programming Boards category; Hello, I have been struggling with a memory corruption/crash that causes the message in the subject and humbly ask for ...

  1. #1
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    _BLOCK_TYPE_IS_VALID(pHead -> nBlockUse)

    Hello,
    I have been struggling with a memory corruption/crash that causes the message in the subject and humbly ask for your help.
    I narrowed down the code to just a few lines hopefully it will be easy to see what is that I'm doing wrong.
    Here is the main program
    Code:
    #include "example.h"
    #include <vector>
    int main()
    {
        std::vector<exampleClass> objs;
        exampleClass test;
        objs.push_back(test);
        return 0;
    }
    And here is the header that defines the classes and the implementation:
    Code:
    class Curve
    {
    private:
        double *m_x;
    public:
        Curve(int n, double *x)
        {
            m_x = new double[n];
        }
        ~Curve()
        {
            delete [] m_x;
        }
    };
    ///////////////////////////////////
    class exampleClassComp
    {
    private:
        double val;
        Curve cv;
    public:
        exampleClassComp() : cv(0,0)
        { }
    friend class exampleClass;
    };
    //////////////////////////////
    class exampleClass
    {
    private:
        int id;
        exampleClassComp obj;
    public:
        exampleClass(void); 
    };
    ///////////////////////////////
    exampleClass::exampleClass(void)
    {
        id = 0;
        obj.val = 0.0;
    }
    It seems that the crash occurs in the dst of the class Curve. Also, I noticed that it is called when the object "test" is pushed onto the vector.
    If anyone can offer some insight it would be much appreciated!
    Thanks!

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
    Join Date
    Oct 2007
    Posts
    22,765
    The problem is that your class lacks a copy constructor.
    The same pointer is copied to two objects (one when creating it and one when pushing it into the vector), so the destructor tries to delete the same memory twice.
    Either you need to perform a deep copy (ie allocate new storage in new object and copy data over) or make the copy constructor private.
    Last edited by Elysia; 06-05-2008 at 07:24 AM.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  3. #3
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    Thanks for the reply.
    I am assuming that the class that needs to have copy constructor and overloaded operator = is the Curve class.
    I will give it a shot and report.
    Thanks again.
    Andrea.

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