请指点Bug在哪里

ProgrammingRing 2013-04-25 08:03:54

下面的代码的标记处说是个bug，我实在看不明白那里为什么是个bug，请指点那里为什么是bug啊...



class CMyString

{

public:

	CMyString();

	CMyString(CMyString& obj);

	CMyString(char *pstrBuff);

	~CMyString();



	void SetString(char *pstrBuff);

	char* GetString();

	

	int GetStringLen();



private:

	char *m_pstrBuff;

};



CMyString::CMyString()

{

	m_pstrBuff = NULL;

}

CMyString::CMyString(CMyString& obj)

{

	m_pstrBuff = NULL;

	this->SetString(obj.GetString());

}

CMyString::CMyString(char *pstrBuff)

{

	m_pstrBuff = NULL;

	SetString(pstrBuff);

}

CMyString::~CMyString()

{

	if (m_pstrBuff != NULL)

	{

		delete [] m_pstrBuff;

		m_pstrBuff = NULL;

	}

}



void CMyString::SetString(char *pstrBuff)

{

	if (m_pstrBuff != NULL)

	{

		delete [] m_pstrBuff;

		m_pstrBuff = NULL;

	}



	int nLen = strlen(pstrBuff);

	m_pstrBuff = new char[nLen + sizeof(char)];



	do 

	{

		m_pstrBuff[nLen] = pstrBuff[nLen];

		nLen--;

	} while (nLen >= 0);



}

char* CMyString::GetString()

{

	return m_pstrBuff;

}

int CMyString::GetStringLen()

{

	int nLen = 0;

	do 

	{

		nLen++;

	} while (m_pstrBuff[nLen]);

	return nLen;

}





CMyString ShowString(CMyString MyString)

{

	CMyString MyStringRet;



	char szBuff[50] = {0};

	scanf("%50s", szBuff);



	printf("%s\r\n", MyString.GetString());



	MyStringRet.SetString(szBuff);



	return MyStringRet;

}



int main(int argc, char* argv[])

{

	char szBuff[50] = {0};

	scanf("%50s", szBuff);

	CMyString * pMyString = NULL;



	CMyString MyString(szBuff);

	

	CMyString MyStringRet = ShowString(MyString);



	printf("%s\r\n", MyStringRet.GetString());





	// 堆对象的使用

	pMyString = new CMyString[2];



	if (pMyString == NULL)

	{

		return -1;

	}



	pMyString[0].SetString(MyStringRet.GetString());

	pMyString[1].SetString(MyString.GetString());

	printf("%s %s\r\n", (*pMyString).GetString(), (*(pMyString+1)).GetString());



	if (pMyString != NULL)

	{

		delete [] pMyString;		// BUG所在处

		pMyString = NULL;

	}

	

	return 0;

}

...全文

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bsnry 2013-04-29

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sscanf用错了。 49就行了，会自动加上一个'\0'. 另外：每次sscanf会从控制台的缓冲区里再次提取数据。所以: 使用之前 fflush(stdin)一次

引用楼主 ProgrammingRing 的回复:

下面的代码的标记处说是个bug，我实在看不明白那里为什么是个bug，请指点那里为什么是bug啊...


class CMyString
{
public:
	CMyString();
	CMyString(CMyString& obj);
	CMyString(char *pstrBuff);
	~CMyString();

	void SetString(char *pstrBuff);
	char* GetString();
	
	int GetStringLen();

private:
	char *m_pstrBuff;
};

CMyString::CMyString()
{
	m_pstrBuff = NULL;
}
CMyString::CMyString(CMyString& obj)
{
	m_pstrBuff = NULL;
	this->SetString(obj.GetString());
}
CMyString::CMyString(char *pstrBuff)
{
	m_pstrBuff = NULL;
	SetString(pstrBuff);
}
CMyString::~CMyString()
{
	if (m_pstrBuff != NULL)
	{
		delete [] m_pstrBuff;
		m_pstrBuff = NULL;
	}
}

void CMyString::SetString(char *pstrBuff)
{
	if (m_pstrBuff != NULL)
	{
		delete [] m_pstrBuff;
		m_pstrBuff = NULL;
	}

	int nLen = strlen(pstrBuff);
	m_pstrBuff = new char[nLen + sizeof(char)];

	do 
	{
		m_pstrBuff[nLen] = pstrBuff[nLen];
		nLen--;
	} while (nLen >= 0);

}
char* CMyString::GetString()
{
	return m_pstrBuff;
}
int CMyString::GetStringLen()
{
	int nLen = 0;
	do 
	{
		nLen++;
	} while (m_pstrBuff[nLen]);
	return nLen;
}


CMyString ShowString(CMyString MyString)
{
	CMyString MyStringRet;

	char szBuff[50] = {0};
	scanf("%50s", szBuff);

	printf("%s\r\n", MyString.GetString());

	MyStringRet.SetString(szBuff);

	return MyStringRet;
}

int main(int argc, char* argv[])
{
	char szBuff[50] = {0};
	scanf("%50s", szBuff);
	CMyString * pMyString = NULL;

	CMyString MyString(szBuff);
	
	CMyString MyStringRet = ShowString(MyString);

	printf("%s\r\n", MyStringRet.GetString());


	// 堆对象的使用
	pMyString = new CMyString[2];

	if (pMyString == NULL)
	{
		return -1;
	}

	pMyString[0].SetString(MyStringRet.GetString());
	pMyString[1].SetString(MyString.GetString());
	printf("%s %s\r\n", (*pMyString).GetString(), (*(pMyString+1)).GetString());

	if (pMyString != NULL)
	{
		delete [] pMyString;		// BUG所在处
		pMyString = NULL;
	}
	
	return 0;
}

引用楼主 ProgrammingRing 的回复:

下面的代码的标记处说是个bug，我实在看不明白那里为什么是个bug，请指点那里为什么是bug啊...


class CMyString
{
public:
	CMyString();
	CMyString(CMyString& obj);
	CMyString(char *pstrBuff);
	~CMyString();

	void SetString(char *pstrBuff);
	char* GetString();
	
	int GetStringLen();

private:
	char *m_pstrBuff;
};

CMyString::CMyString()
{
	m_pstrBuff = NULL;
}
CMyString::CMyString(CMyString& obj)
{
	m_pstrBuff = NULL;
	this->SetString(obj.GetString());
}
CMyString::CMyString(char *pstrBuff)
{
	m_pstrBuff = NULL;
	SetString(pstrBuff);
}
CMyString::~CMyString()
{
	if (m_pstrBuff != NULL)
	{
		delete [] m_pstrBuff;
		m_pstrBuff = NULL;
	}
}

void CMyString::SetString(char *pstrBuff)
{
	if (m_pstrBuff != NULL)
	{
		delete [] m_pstrBuff;
		m_pstrBuff = NULL;
	}

	int nLen = strlen(pstrBuff);
	m_pstrBuff = new char[nLen + sizeof(char)];

	do 
	{
		m_pstrBuff[nLen] = pstrBuff[nLen];
		nLen--;
	} while (nLen >= 0);

}
char* CMyString::GetString()
{
	return m_pstrBuff;
}
int CMyString::GetStringLen()
{
	int nLen = 0;
	do 
	{
		nLen++;
	} while (m_pstrBuff[nLen]);
	return nLen;
}


CMyString ShowString(CMyString MyString)
{
	CMyString MyStringRet;

	char szBuff[50] = {0};
	scanf("%50s", szBuff);

	printf("%s\r\n", MyString.GetString());

	MyStringRet.SetString(szBuff);

	return MyStringRet;
}

int main(int argc, char* argv[])
{
	char szBuff[50] = {0};
	scanf("%50s", szBuff);
	CMyString * pMyString = NULL;

	CMyString MyString(szBuff);
	
	CMyString MyStringRet = ShowString(MyString);

	printf("%s\r\n", MyStringRet.GetString());


	// 堆对象的使用
	pMyString = new CMyString[2];

	if (pMyString == NULL)
	{
		return -1;
	}

	pMyString[0].SetString(MyStringRet.GetString());
	pMyString[1].SetString(MyString.GetString());
	printf("%s %s\r\n", (*pMyString).GetString(), (*(pMyString+1)).GetString());

	if (pMyString != NULL)
	{
		delete [] pMyString;		// BUG所在处
		pMyString = NULL;
	}
	
	return 0;
}

引用楼主 ProgrammingRing 的回复:

下面的代码的标记处说是个bug，我实在看不明白那里为什么是个bug，请指点那里为什么是bug啊...


class CMyString
{
public:
	CMyString();
	CMyString(CMyString& obj);
	CMyString(char *pstrBuff);
	~CMyString();

	void SetString(char *pstrBuff);
	char* GetString();
	
	int GetStringLen();

private:
	char *m_pstrBuff;
};

CMyString::CMyString()
{
	m_pstrBuff = NULL;
}
CMyString::CMyString(CMyString& obj)
{
	m_pstrBuff = NULL;
	this->SetString(obj.GetString());
}
CMyString::CMyString(char *pstrBuff)
{
	m_pstrBuff = NULL;
	SetString(pstrBuff);
}
CMyString::~CMyString()
{
	if (m_pstrBuff != NULL)
	{
		delete [] m_pstrBuff;
		m_pstrBuff = NULL;
	}
}

void CMyString::SetString(char *pstrBuff)
{
	if (m_pstrBuff != NULL)
	{
		delete [] m_pstrBuff;
		m_pstrBuff = NULL;
	}

	int nLen = strlen(pstrBuff);
	m_pstrBuff = new char[nLen + sizeof(char)];

	do 
	{
		m_pstrBuff[nLen] = pstrBuff[nLen];
		nLen--;
	} while (nLen >= 0);

}
char* CMyString::GetString()
{
	return m_pstrBuff;
}
int CMyString::GetStringLen()
{
	int nLen = 0;
	do 
	{
		nLen++;
	} while (m_pstrBuff[nLen]);
	return nLen;
}


CMyString ShowString(CMyString MyString)
{
	CMyString MyStringRet;

	char szBuff[50] = {0};
	scanf("%50s", szBuff);

	printf("%s\r\n", MyString.GetString());

	MyStringRet.SetString(szBuff);

	return MyStringRet;
}

int main(int argc, char* argv[])
{
	char szBuff[50] = {0};
	scanf("%50s", szBuff);
	CMyString * pMyString = NULL;

	CMyString MyString(szBuff);
	
	CMyString MyStringRet = ShowString(MyString);

	printf("%s\r\n", MyStringRet.GetString());


	// 堆对象的使用
	pMyString = new CMyString[2];

	if (pMyString == NULL)
	{
		return -1;
	}

	pMyString[0].SetString(MyStringRet.GetString());
	pMyString[1].SetString(MyString.GetString());
	printf("%s %s\r\n", (*pMyString).GetString(), (*(pMyString+1)).GetString());

	if (pMyString != NULL)
	{
		delete [] pMyString;		// BUG所在处
		pMyString = NULL;
	}
	
	return 0;
}

ProgrammingRing 2013-04-25

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我也觉得没bug，可是那里标注了有bug……不会是标错了吧..

lzjamao 2013-04-25

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引用 4 楼 MAOMAOXIAOHUO 的回复:

我用VS2010运行的，LZ说的BUG，

我用VS2010运行的，没有LZ说的BUG

lzjamao 2013-04-25

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我用VS2010运行的，LZ说的BUG，

palm008 2013-04-25

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你在

void CMyString::SetString(char *pstrBuff)

中已经删除字符串了，怎么对字符串又进行strlen呢？

nirvana_newbie 2013-04-25

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windowsXP下VC6.0编译无错，运行无内存泄露问题。此图见证：

大神送一血 2013-04-25

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ShowString 返回局部对象，析构后指针为空，然后又delete空指针？

ProgrammingRing 2013-04-25

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调试半天，还是看不出那里为啥是个bug……难道是书的作者搞错了？放了一个没bug的代码，还是我没看出？还再请大牛过过眼

赵4老师 2013-04-25

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对学习编程者的忠告：眼过千遍不如手过一遍！书看千行不如手敲一行！手敲千行不如单步一行！单步源代码千行不如单步对应汇编一行！单步类的实例“构造”或“复制”或“作为函数参数”或“作为函数返回值返回”或“参加各种运算”或“退出作用域”的语句对应的汇编代码几步后，就会来到该类的“构造函数”或“复制构造函数”或“运算符重载”或“析构函数”对应的C/C++源代码处。 VC调试时按Alt+8、Alt+7、Alt+6和Alt+5,打开汇编窗口、堆栈窗口、内存窗口和寄存器窗口看每句C对应的汇编、单步执行并观察相应堆栈、内存和寄存器变化，这样过一遍不就啥都明白了吗。对VC来说，所谓‘调试时’就是编译连接通过以后，按F10或F11键单步执行一步以后的时候，或者在某行按F9设了断点后按F5执行停在该断点处的时候。

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