帮助！！！ ---“表达式:_CrtIsValidHeapPointer(pUserData)" [英] Help!!! --- "Expression: _CrtIsValidHeapPointer(pUserData)"

问题描述

大家好:

这张图片有什么问题--表达式:_CrtIsValidHeapPointer(pUserData)".

在类中调试时捕获了异常，代码如下:

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;
}

我的项目比这里介绍的要复杂，但是有关"m_data"用法的上下文几乎相同.

我试图释放m_data的内存删除[] m_data"时出了什么问题，该如何避免呢?

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?

推荐答案

第一次进入时，指针不是指向堆内存:它是指向静态内存！

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

m_data = "You are someone!!";

使用m_data的方式是胡说八道.
查看MyClass::MyClass构造函数，首先从堆中分配50个字符，将地址分配给m_data，然后将常量"You are someone"的地址分配给m_data.从这一点开始，您分配的50个字符将泄漏(并且不可访问)，其中m_data指向常量文字，您稍后尝试在析构函数和SetStr中删除它们.

在MyClass :: SetStr中有一个(NULL == para)return;.如果将if放在前面(这是拼写错误！！?)，这会更有意义.

实际上，字符串文字和字符数组无法按照您的想法工作.
特别是

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!!";

不将字符串复制到m_data指向的数组中.

要正确复制，您应该使用strcpy 之类的库函数或类似的函数，其工作原理如下:

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:

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';
}

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