2d arrays using dynamic memory

[obdo]

Hey, I'm trying to make 2d arrays using dynamic memory in c++.

I have been looking up ways to do this but a lot of them seem pretty complicated (and disputed).

I am using a current g++ compiler for this.

I was hoping I could just do
cmdList = new char[5][21]
but I am pretty sure I need to use pointers for the compiler to be able to do it.

I need to do this in 2 seperate constructors, a default with a preset amount, and what you see below that will match it to [num_of_cmds][21].

//	ROBOT CONSTRUCTOR with 2 paramers
Robot::Robot(int num_of_cmds, const char *nm) {
	//	Load Robot name
	size = (nm == NULL) ? 0 : strlen(nm);

	try {
		name = new char[size + 1];
	}
	catch(std::bad_alloc) {
		cout << "Error allocating " << size + 1 << " bytes of memory\n";
		name = NULL;
	}
	
	if (name) {
		strcpy (name, nm);
	}
	
	//	Allocate memory for command array
	//	cmdList = new char[num_of_cmds][21] <-- Doesn't work

};

And for the sake of context, the relevent class:

//	ROBOT CLASS
class Robot {
	private:
		char *name;
		char *cmdList;
		int size;
	public:
		Robot( );
		Robot(int num_of_cmds, const char *nm);
		~Robot( );
	
};

Any help is appreciated, this topic has been stumping me for a bit now

[Disch]

You can save yourself a million headaches by using actual strings instead of char arrays. Then you don't need to have 2D arrays, either... just have a 1D array of strings.

Or better yet, a vector of strings:

std::vector< std::string > cmdList;

cmdList.resize(10);  // I want 10 strings in this array
cmdList[0] = "First string";
cmdList[1] = "Second string";
//... 

What's even better is that vector and string internally handle the cleanup, so you don't have to use new/delete.

[obdo]

Wow, that is so much simpler.

Will this allocate the memory needed with
cmdList.resize(10)

In my constructors I am only supposed to allocate enough memory for the commands, I have another function (I have already written) that will initialize the strings with actual data.

[Disch]

Yes, resize() will allocate all the necessary memory.

Of course if you are using std::string, do not use strcmp, strcpy, etc functions, as those are only to be used with char arrays. With strings you don't need them.

[obdo]

Now my program is functioning :)
I haven't used vector at all before this but I think it is definetly something I need to be looking into.
Thank you

[GFreak45]

I would try learning dynamic arrays as soon as possible if your vectors get large, because they get enormously inefficient, its not actually a limitless array, when it resizes it, it creates a new array transfers all the members up to the smallest size of the 2 arrays and uses the new array, so imagine transfering over 100 values, it gets bad when you get that high

[Disch]

vector is not inefficient when used properly.

it's true that you want to keep resizing to a minimum... or at least if you anticipate future growth, you should reserve() however much you need.

But if you do that, then vector performs very well.

[o1vk4iN6]

This is no problem, you can use reserve() to make the vector big enough to not reallocate.