Array Size confusion

[Prediluted]

Hey everyone, I have a problem that is really puzzling...

I have the following code:

	// Determine size of transfer
	packageSize = strlen( TxBuffer );
	cout << "packageSize "<< packageSize << endl;
	char* RxBuffer = new char [ packageSize ];
	cout << "RxBuffer " << strlen ( RxBuffer ) << endl;
	// Zero out the Rx buffer
	memset( RxBuffer, 0xa5, packageSize );
	cout << "packageSize "<< packageSize << endl;
	cout << "RxBuffer " << strlen(RxBuffer) << endl;

When executed with some TxBuffer length 16 i get this:
packageSize 16
RxBuffer 32
packageSize 16
RxBuffer 32

When I change my code to

	// Determine size of transfer
	packageSize = strlen( TxBuffer );
	cout << "packageSize "<< packageSize << endl;
	char* RxBuffer = new char [ packageSize/2 ];
	cout << "RxBuffer " << strlen ( RxBuffer ) << endl;
	// Zero out the Rx buffer
	memset( RxBuffer, 0xa5, packageSize/2 );
	cout << "packageSize "<< packageSize << endl;
	cout << "RxBuffer " << strlen(RxBuffer) << endl;

The output is like this:

packageSize 16
RxBuffer 24
packageSize 16
RxBuffer 24

I'm not sure why the sizes are even different, and even more strangly, why is dividing a 32 size by 2 giving me 24?

[tabstop]

The number you get from strlen bears no relationship to the amount of memory you set aside. The number you get from strlen is "how many bytes is it from here to the next \0 character?" and if that happens to be 24 bytes away, then there you go.

[Prediluted]

Ok that makes sense. Then how do I set it so the RxBuffer will have the same size as the TxBuffer that is already filled with data of unknown size? Is there a better method to use then strlen?

[tabstop]

You are already setting the size of the buffer when you create it.

Once you create it, there is no way to retrieve the size of the buffer, so don't try. It's up to you to remember what it was.

Another thing to remember: if you are using C-string utilities, many of them require (just as strlen does) the last character of the data to be \0. Presumably the way you are getting TxBuffer makes sure that \0 is there. strlen requires the \0 character, but it does not count it -- so when you create the new buffer you must add one extra character to account for it, if you intend for Tx and Rx to "be the same size".

[King Mir]

In order to 0 out an array you need to set it's values to 0, not 0xa5.

Also, reading passed the end of your allocated space can in rare cases cause your program to crash.

[Elysia]

You might find std::vector useful here. It allows you to find out its size and dynamically reallocate it easily. It also takes care of freeing memory.
Memory is also contiguous, so it works exactly like a buffer.
To get a pointer to the buffer, you might simply do &vec[0].