Can I execute a "variable statements" within a function and without defines.
- by René Nyffenegger
I am facing a problem that I cannot see how it is solvable without #defines or incuring a performance impact although I am sure that someone can point me to a solution.
I have an algorithm that sort of produces a (large) series of values. For simplicity's sake, in the following I pretend it's a for loop in a for loop, although in my code it's more complex than that.
In the core of the loop I need to do calculations with the values being produced. Although the algorithm for the values stays the same, the calculations vary.
So basically, what I have is:
void normal() {
// "Algorithm" producing numbers (x and y):
for (int x=0 ; x<1000 ; x++) {
for (int y=0 ; y<1000 ; y++) {
// Calculation with numbers being produced:
if ( x+y == 800 && y > 790) {
std::cout << x << ", " << y << std::endl;
}
// end of calculation
}}
}
So, the only part I need to change is
if ( x+y == 800 && y > 790) {
std::cout << x << ", " << y << std::endl;
}
So, in order to solve that, I could construct an abstract base class:
class inner_0 {
public:
virtual void call(int x, int y) = 0;
};
and derive a "callable" class from it:
class inner : public inner_0 {
public:
virtual void call(int x, int y) {
if ( x+y == 800 && y > 790) {
std::cout << x << ", " << y << std::endl;
}
}
};
I can then pass an instance of the class to the "algorithm" like so:
void O(inner i) {
for (int x=0 ; x<1000 ; x++) {
for (int y=0 ; y<1000 ; y++) {
i.call(x,y);
}}
}
// somewhere else....
inner I;
O(I);
In my case, I incur a performance hit because there is an indirect call via virtual function table. So I was thinking about a way around it. It's possible with two #defines:
#define OUTER \
for (int x=0 ; x<1000 ; x++) { \
for (int y=0 ; y<1000 ; y++) { \
INNER \
}}
// later...
#define INNER \
if (x + y == 800 && y > 790) \
std::cout << x << ", " << y << std::endl;
OUTER
While this certainly works, I am not 100% happy with it because I don't necessarly like #defines.
So, my question: is there a better way for what I want to achieve?
