C / C++ / MFC

kumar_windows wrote:

which ( userdefined or default copy --- constructor/ overloaded assignment operator) performs what ( deep/ shallow copy)?

toxcct wrote:

i don't know what is a deep copy nor shallow copy

toxcct wrote:

in general, it is bad to copy only the addresses

led mike wrote:

Well you better get busy telling the rest of the industry that because there is a common design pattern known as "copy on write" that calls for doing just that.

led mike wrote:

At one time, maybe still... i don't know, CString used that design.

<br />
class Shallow<br />
{<br />
private:<br />
	char* m_MyString;<br />
public:<br />
	Shallow() { m_MyString = new char[20]; }<br />
	~Shallow() { delete [] m_MyString; }<br />
};<br />
<br />
class Deep<br />
{<br />
private:<br />
	char* m_MyString;<br />
public:<br />
	Deep() { m_MyString = new char[20]; }<br />
	Deep(const Deep& d) { memcpy(m_MyString, d.m_MyString); }<br />
	~Deep() { delete [] m_MyString; }<br />
	const Deep& operator= (const Deep& d) { memcpy(m_MyString, d.m_MyString); }<br />
};<br />
<br />
void main()<br />
{<br />
	Shallow a, b;<br />
	Deep c, d;<br />
<br />
	// shallow copy<br />
	a = b;	// this will cause a.m_MyString == b.m_MyString<br />
		// this will also cause an error when the objects go out of scope<br />
		// since the pointer will be deleted twice!<br />
<br />
	// deep copy<br />
	c = d;	// this will cause c.m_MyString != d.m_MyString<br />
		// however, strcpy(c.m_MyString, d.m_MyString) == 0<br />
		// that is, now there are 2 copies of the string<br />
}<br />

Zac Howland wrote:

IN GENERAL, it is a bad idea to simply copy the addresses.

Zac Howland wrote:

Not CString,

BKhandelwal wrote:

with this map i find my function address that i saved previosly and call my function but in this code i have problem with find()..

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

CString str;
double mydbl = 0.17000;
std::ostringstream ss;
ss << mydbl;
str = ss.str().c_str();
MessageBox( str);

blacksalt wrote:

My qstn is how to use C in an MFC [exe] project

extern "C"
{
    void prn();
}