Thread: How to free memory ?

> where should i free memory in class with distructor ?
Yes, you should free memory in the destructor.

> if i do that i am getting exception.
That's because your code is full of bugs.
1. You don't have a proper constructor to begin with, which at least sets pName = NULL;
2. Mixing new and malloc/realloc is a bad thing to do. Since this is C++, you should be using new for everything.

> void main()
See the FAQ - main returns int.

You should really use std::string instead of char* in which case you wouldn't need practically any of this code.

thx salem,
Did operator "new" resembles to "realloc" functionality ?
say i initilization for pointer in constructor and free memory in destructor. still my code
gives run time error at destructor.
i have just switched from C to C++ programming.

Code:

---------------
test.h file
---------------------------
class demon
{
	
	char* pName;
	int nVal,nLen;
	
public:
	
	demon():nVal(0),nLen(0)
	{
	pName = NULL;
	}
	
	
	demon operator= (const demon& d)
	{
		if(this != &d)
		{
			this->pName = new char(strlen(d.pName)+1);
			memset(this->pName,0,strlen(d.pName)+1);
			strcpy(pName,d.pName);
			this->nVal = d.nVal;
		}
		return *this;
	}
	
	
	void set(int x,char* pstring)
	{
		nVal = x;
		pName = (char*)malloc(strlen(pstring)+1);
		memset(this->pName,0,strlen(pstring)+1);
		strcpy(pName ,pstring);
	}
	
	void get()
	{
		cout<<nVal<<endl<<pName<<endl;
	}
	
	demon operator + (const demon& d1)//,const demon d2);
	{
		
		nLen =strlen(this->pName)+1;
		nLen += strlen(d1.pName)+1;
		
		this->pName = (char*)realloc(this->pName,nLen);

		memset(this->pName,0,nLen);
		strcat(this->pName, d1.pName);
		return *this;
	}

	~demon()
	{
	delete(pName);
	}
	
};

-----------------------
in test.cpp file
---------------------------
main()
{
	
	demon obj_demon, obj_demon1, obj_demon2  ;
	
	obj_demon.set(25,"mySample");
	
	obj_demon2.set(45,"Overload demo");
	
    obj_demon =  obj_demon + obj_demon2; 
	
	
	obj_demon.get();
	obj_demon2.get();
	
	return 0;
}

To allocate a char array use square brackets:

Code:

pName = new char[how_many];
...
delete [] pName;

In addition you'll need a copy constructor. And the assignment operator leaks memory because you don't free the old memory before you request for new memory.

You shouldn't be using realloc with a pointer that you obtained with new (in C++ you'd just free previous memory and allocate a larger new block).

By the way, for a char* alloc, free and realloc would be fine if you want to stick with char arrays. If you want to write programs, though , and not just sweat over the low-level char array manipulation, strings are preferable.

Here's what the same code would look like, using C++ string class.

Code:

#include <string>

class demon
{
	
	string Name;
	int nVal;
	
public:
	
	demon():nVal(0) {}	
			
	void set(int x, string s)
	{
		nVal = x;
		Name = s;
	}
	
	void get()
	{
		cout<<nVal<<endl<<Name<<endl;
	}
	
	demon operator + (const demon& d1)
	{
		
		Name += d1.Name;
		return *this;
	}	
};

Note, that neither copy constructor, assignment operator nor destructor is needed, as the default ones that the compiler produces are good enough.

> Did operator "new" resembles to "realloc" functionality ?
There is no C++ operator which resembles realloc in C.
You have to call new[ ] for some new memory, followed by a manual copy in your code (use a for loop), and a delete[ ] of the old memory.

And you're still mixing new with malloc/realloc.

> demon():nVal(0),nLen(0)
Why not
demon():nVal(0),nLen(0),pName(0)

> main()
It's better than void, but why not just be specific and say
int main()

operator + should not modify either of the operands. Declare the function as const and correct the behaviour, or better yet, use the two-parameter friend version with both parameters as const.