The C++ Preprocessor - which is in fact the same as the C Preprocessor - provides some very basic, but powerful abilities. I haven't used them quite often, but I have seen some nice examples. So here are some C++ Preprocessor Snippets:
Maximum / Minimum
If you want to find the maximum / minimum of two elements, no matter of which type, you can do something like this:
#include <iostream>
#define MAX(a, b) ((a < b) ? b : a)
using namespace std;
int main() {
cout << MAX(42, 1337) << endl;
cout << MAX(1337, 42) << endl;
cout << MAX(-1337, 42) << endl;
cout << MAX(1337.0, 42) << endl;
return 0;
}
Absolute Value
You can get the absolute value like this:
#include <iostream>
#define ABS(a) (a < 0 ? -(a) : a)
using namespace std;
int main() {
int a = 42, b = -43, c = 0, d = -1337;
cout << ABS(a) << endl;
cout << ABS(b) << endl;
cout << ABS(c) << endl;
cout << ABS(d) << endl;
return 0;
}
By the way, brackets around a are important, because without them you could get:
a=1,b=3
ABS(a-b) = ABS(1-3) = (1-3 < 0 ? -1-3 : 1-3) = -2 < 0 ? -4 : -2 = -4
Swap variable content
This is an example for a multiline replacement.
#include <iostream>
#define SWAP(a, b) { int tmp; \
tmp = b; \
b = a; \
a = tmp; \
}
using namespace std;
int main() {
int a = 42, b = 1337;
swap(a, b);
cout << a << endl;
cout << b << endl;
return 0;
}
See also
- Wikipedia: C preprocessor
- Tips and tricks using the preprocessor: Part one - part two
A very good article about the meaning of #import, #error, #pragma. It is written very well and has some examples. - Obfuscated C: Calculate PI
Do you know more preprocessor snippets that are used very often or which are interesting?