left Operand must be l-value

Kryogenik · 2010-11-15T04:05:44

So yeah. I have an array that is a pointer to a pointer of my class CXFile, I declared it like this.CXFile** Objects;And allocated the array like this (Object Nums equals 2 BTW)Objects=new CXFile* [ObjectNums];I can use this array to control classes pointed to by the array, and it's pretty good. The only problem is that I don't know how to check if a certain value in the array has been initialized.I know what the error means from a google search. It means that the number on the left side of the operator (== in my case) must be a variable or something, like you couldn't do this.int=32But I couldn't find anyone who had quite the same problem I'm having on google. I want to see if it is used yet because when you load an object in my little engine, you can specify a spot in the array you want it to be in, or you can set it to -1 and it will find a free spot to put it in for you. But I don't know how to check if a slot is free or not and thats the problem I'm having. I tried to use this to check if it was free, but it doesn't work and gives me the above error.if(Objects[x]==0) //Do stuff that would happen if the slot was freeWhat should I do? In a nutshell, how do I check if a spot in my CXFile** array has been used yet? Thanks for any help.

Graphics and GPU Programming Programming

Started by Kryogenik November 11, 2010 05:19 AM

11 comments, last by phresnel 13 years, 5 months ago

Kryogenik

102

Author

November 14, 2010 05:10 AM

I set all the values in the array to zero and it worked. Also, in this if statement

if (Objects[x]==0)

I also had this in it

if (Objects[x]==0 && done=0)

I forgot the extra equal sign next to done, so that was probably a problem as well. Kind of a dumb mistake XD

Kryogenik

102

Author

November 14, 2010 02:49 PM

Sorry to double post, but I ran into another problem with this array (so much for getting it working XD). How do I delete all the class objects and the array?
I thought it would be like this:

for (int i=0;i<ObjectNum;i++)
delete Objects;Objects=0;

Or this:

delete [] Objects;Objects=0;

Or both of them, but I've tried both of them seperately and together, and I get memory leaks. I checked for them by putting this at the top of the WinMain

#if defined(DEBUG) | defined(_DEBUG)
_CrtSetDbgFlag( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF );

So anyway, how do I delete all the class objects and the array? The array is a pointer to a pointer of an abstract class, it looks like this

CXFile** Objects;
Objects=new CXFile* [2];

And the pointers point to pointers of objects of either my CXFileStatic class or my CXFileEntity class, not CXFile. Does that cause problems when calling delete? Thanks for any help.

phresnel

953

November 15, 2010 04:05 AM

Quote:Original post by Kryogenik
I set all the values in the array to zero and it worked. Also, in this if statement

if (Objects[x]==0)

I also had this in it

if (Objects[x]==0 && done=0)

I forgot the extra equal sign next to done, so that was probably a problem as well. Kind of a dumb mistake XD

That is why we ask to post actual code, not code that you think is wrong. if (Objects[x]==0) is perfectly valid, whereas done=0 is not necessarily valid.

for (int i=0;i<ObjectNum;i++)delete Objects;Objects=0;

This is prolly not valid C++ and definitely not what you want. Let me enlighten you:

for (int i=0;i<ObjectNum;i++)    delete Objects;Objects=0;

In case you have no variable i declared above the for loop, this will luckily not compile. You need braces if you have more than statement in the for-loop.

Here is the proper way to delete the array:

for (int i=0;i<ObjectNum;i++) {    if (Objects) delete Objects;}delete [] Objects;

Rules-of-thumb:

Use free() after malloc().

Use delete after new.

Use delete [] after new [].

Also, have you heard of boost::shared_ptr?

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left Operand must be l-value

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