Question

Ok, I’m coming from vb.net to c++. Im trying to use vectors in a structure, but the compiler yells at at me for it. What is wrong with the current statement?

#include <vector>

struct FactorSet
{
 vector<long long> UpperFactor(0);
 vector<long long> LowerFactor(0);
};

Output error (Visual Studio 2008):

Error 1 error C2059: syntax error : ‘constant’

I venture to guess it is my lack of understanding of what a vector really is. In my mind it is an object, although I think its whats called a template. Other objects like strings seem to have no problem. I also assume this is extended to class definitions as well since structures and classes are so similar.

Answer 1

You want:

#include <vector>

struct FactorSet
{
 std::vector<long long> UpperFactor;
 std::vector<long long> LowerFactor;
};

though you might also have problems with long long, as this is not currently part of C++.

If you actually want to give a size to the vectors, you need to do that via the structs constructor:

struct FactorSet
{
 std::vector<long long> UpperFactor;
 std::vector<long long> LowerFactor;

 FactorSet() : UpperFactor(42), LowerFactor(42) {}
};

So now when you say:

FactorSet f;

the vectors in f will both have size 42.

As to what a vector actually is, it’s a class very like a string, except in the case of the vector you have to say what type of thing it contains. So

vector <char> s;

is very similar (but not identical) to:

string s;