C++ sizeof C-style string / char array - optimization

Question

I\'m a student at university. I work mostly with Java, C++ is very new to me, so I probably make many silly mistakes and I have upcoming exams to cope with. Don\'t be too harsh

Answer 1

I think you are expecting the sizeof operator to behave differently than it actually does. Let's take this code, for example:

const char* str = new char[137];

Here, if you write sizeof(str) you'll probably either get 4 or 8, depending on your system, because sizeof(str) measures the number of bytes of the pointer str itself rather than the number of bytes in the array pointed at by str. So, on a 32-bit system, you'd probably get 4, and on a 64-bit system you'd probably get 8, independently of how many characters you allocated.

Unfortunately, C++ doesn't have a way for you to get the number of characters or the memory used up by a dynamically allocated array. You just have to track that yourself.

Similarly, in your main function, when you write sizeof(p), you're measuring the number of bytes used by the object p, not the total number of bytes used by p and the arrays it points at. You'll always get back the same value for sizeof(p) regardless of what strings it points at.

If you're planning on working with strings in C++, I strongly recommend using std::string over raw C-style strings. They're much easier to use, they remember their length (so it's harder to mix up strlen and sizeof), and if you have a class holding s bunch of std::strings you don't need a copy constructor or assignment operator to handle the logic to shuffle them around. That would significantly clean up your code and eliminate most of the memory errors in it.