Intimidat0r

I am trying to help someone translate a large app from VB.NET into C++. There are alot of ReDim statements in the code. I know what ReDim does in VB.NET but I was wondering if there was a way to do such a thing in C++. Alot of the time, it's mostly this:


Any insights would be greatly appreciated!

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DaWei

If you use STL thangys, such as a vector, you have the resize and reserve methods available. If you use malloc for an array, you can realloc. I'm not sure about "new", other than it winds up calling malloc, itself.

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prolog

Hi,

For the first case you can use realloc. But be aware that using realloc on an object created with the new-operator will lead to undefined behavior.

For the second case u can use realloc too, but remember that changing the size to size less than the original will eat oldsize-newsize bytes of data. Again don't mix op-new and malloc/realloc. Also remember to call the right cleanup routine, free() or op-delete.

If you want such behavior think about using std::vector or std::deque which might have some advanteges depending on your particular situation.

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grumpy

While it's true quite a few implementations (i.e. compilers and libraries) do it, there is no requirement for operator new to call malloc().

As you say, the methods to resize an array depend on what you're calling an array;

std::vector has resize() and reserve() methods;

if you've created the array dynamically with malloc, either use realloc(), or replicate the operation using malloc(), copying the old array to the newly allocated memory, free() up the old array, and then reassign the pointer to point at the new array.

if you've created the array dynamically with operator new[], allocate a new array with operator new[], copy the old array to the newly allocated array, delete[] the old array, and reassign the pointer to point at the new array.

With a standard array, for example;
there is no way in C++ of resizing it.

uman

you shouldn't be doing this with arrays; use vectors.

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