大小可变的2D结构数组成员变量

Question

So I've got a class that I'm generalizing into a base class. One of the member variables is a 2D array of a struct.

struct SomeType
{
...
}

and then in the class's header:

SomeType member_variable_ [SIZE_ONE][SIZE_TWO];

But, in my situation, SIZE_TWO needs to be set when the class is initialized because it's going to be different depending on what's using this. What's the best way to have a 2D struct array with a size that's not yet set as a member variable?

Answer 1

The simplest way to solve it is to not use C-style arrays at all, but to use std::vector . Or possibly an std::array of vectors:

std::array<std::vector<SomeType>, SIZE_ONE> member_variable_;

Now you can easily insert as many (or as few) SomeType objects as needed, and still use the array-indexing syntax:

member_variable_[some_index][some_other_index]

---

To set a fixed size at runtime for the "second" Dimension, you can do something like this in the constructor:

for (auto& v : member_variable_)
    v = std::vector<SomeType>(the_runtime_size);

Answer 2

You could use a template:

template<unsigned SIZE_TWO>
class theClass
{
     SomeType member_variable_ [SIZE_ONE][SIZE_TWO];

SIZE_TWO will be set when you instantiate the class.

theClass<5> tc; //member_variable_ [SIZE_ONE][5];

You could also use containers like std::vector or std::array .