Macro: pass the content of a variable (example: int) as argument to a macro call

[donelron]

Hi,

I am trying to generate a couple of vectors, but the exact number of vectors that will be needed can only be determined at runtime. Therefore I had the idea to use a macro call and text substitution in order to declare the necessary number of vectors. Unfortunately, the arguments of a macro call are always (as far as I know) considered text only. So, the loop in my example below in which I am trying to generate the following code:

vector<int> vector0;
vector<int> vector1;
vector<int> vector2;
vector<int> vector3;

does not work.

#include <iostream>
#include <vector>
using namespace std;

#define declareVec(vecno) vector<int> vector##vecno;

int main()
{
    for (int i=0;i<4;i++){
       declareVec(i);
    }

    vector0.push_back(666);
    cout << "vector0[0]=" << vector0[0] << endl;

    return 0;
}

I get an an error message 'vector0' was not declared in this scope.

I also tried to initialize a string or char with the content "0" and then pass this string or char to the macro call, but this did not work either.

Is there any way in which I could use the content of an integer variable or any other variable as arguments for a macro call?
Or is there any other method to solve the problem?
Any hints are appreciated!

[Peter87]

Macros are expanded before compilation so they know nothing about what happens at runtime. The compiler will see line 9-11 as

    for (int i=0;i<4;i++){
       vector<int> vectori;;
    }

To be able to have the number of vectors decided at runtime you can store the vectors in a vector.

int main()
{
	std::vector<std::vector<int>> v(4);

	v[0].push_back(666);
	cout << "v[0][0]=" << v[0][0] << endl;

	return 0;
}