(sorry I do not intend to be insolent) ab?a:b operation

cigarstub · 09-27-2005, 08:23 AM

Could you understand the following C header function:
#define a (x, y) xy?x:y

addy86 · 09-27-2005, 09:12 AM

1. Are you sure that there's whitespace between the 'a' and the '('?
2. Have you read a book about C or C++? If not, you should definitely do that. Otherwise you should definitely read it again.
What's it you don't understand? The definition of a macro or the ?: operator?

jtshaw · 09-27-2005, 10:06 AM

That exact syntax seams to be invalid (xy isn't defined) but maybe this will help.

<condition>?<conditons is true>:<condition is false>;

So, in the following code:

Code:

#include <stdio.h>
#define a(x, y) x>y?printf("true\n"):printf("false\n")

int main () {
    a(1,2);
    a(2,1);
    return 0;
}

The output is:

Code:

j_shaw@jshaw ~ $ ./test
false
true

bigearsbilly · 09-29-2005, 03:12 AM

Your example is misquoted.

? ternary op is basically an if/else.
#define is a macro, text is substituted where found.

If you have this file:

Code:

#define largest(x, y) x > y?x:y

#define A "your question"
#define B "answer"
#define C "does this"

main()
{
   largest(10,11);
   char a[] = C B A;
}

and compiile with -E you get something like this:

Code:



main()
{
   10 > 11?10:11;
   char a[] = "does this" "answer" "your question";
}