How to declare a varibale as null

[TnGraham]

I have a program where when I first initialize a CString varibale I want it to be null. I put this:

CString temp = "";

Will this make it null. Because when I put the code below, I get errors:

CString temp = NULL;

[zwA4jE8b]

I believe your first way is correct. The empty string. I don't know about the CString datatype but when comparing strings you don't really compare NULL or not you compare to empty.

[Mathhead200]

If you want to store a NULL value, you need to use pointers. There is no such thing as a NULL object (or reference) in C++.

[ashishkumar]

In case you can overload the copy constructor for CString with arguments of a const char *. Inside that function, check if the passed argument is NULL or not, if it's NULL then initialize it with "" otherwise initialize it with the string provided.

[HenriK]

How about something like this:

#define STR_NULL ""

std::string name = STR_NULL;

[z05DSL3A]

TnGraham wrote:

I have a program where when I first initialize a CString varibale I want it to be null

What exactly do you mean by this? What do you believe null to be or signify?

[sohguanh]

I believe if you are a Java programmer, the null reserved keyword is a familiar term but in C++ I don't think so. I have seen code where C++ coder try to "simulate" by doing a #define null 0

Actually long long time ago the NULL macro exist correct? I use to do if (ptr!=NULL) ... where ptr is a pointer variable. Then later on I have seen code like if (ptr) ...

So are below two statements valid C++ code ?

if (ptr!=NULL)...

if (ptr)...

[Zhuge]

Yes, assuming NULL is defined. It is a standard macro, IIRC, defined as 0. Don't quote me on that though. In C++0x, I recall the nullptr keyword or something similar being introduced.

[sohguanh]

Actually just for curiosity sake, can it happen when the ptr variable do point to the memory address location 0 and there is valid value in that "space" then all hell break loose isn't ?

Unless for most OSes, certain memory address are off-limits to user programs which I believe will include 0x000000....

Hmmm... food for thought.

[Zhuge]

Assigning a pointer in C++ to be 0 doesn't need to be address 0x0 specifically, just any implementation-defined way such that it'll cause an error when dereferenced.

[z05DSL3A]

What I was after (from the OP) is if the aim is to have an CString object with an empty string, in which case the default constructor should suffice i.e. CString temp; .

Or if they are thinking in terms of C# et al String str = null and they are delaying the instantiation of the object to a later time, in which case they would need a point to a CString set to null.