C++ Question
Preprocessor behind the scenes, how does it interpret the following lines of code C++
So i'm using a preprocessing macro for this basic square function :
#define SQUARE(a) a*a
it is then passed to these functions, to perform these tasks respectively:
double f(double x) {
return SQUARE(x);
}
double g(double x) {
return SQUARE(1-x);
}
double h(double x) {
return 1/SQUARE(x);
}
with such functions, for g(x) and h(x) i'm getting results such as:
g(2) = -3, h(2) = 1
g(3) = -5, h(3) = 1
g(4) = -7, h(4) = 1
etc...
I have changed the functions to get their expected results, but I'm curious as to what is happening in the above functions to give me such strange results?
Answer Source
SQUARE(1-x) will be expanded to 1-x*1-x which is not correct at all.
It would be much better to use a function instead of a macro. A function only evaluates the parameter once.
double square(double a)
{ return a * a; }