www.delorie.com/gnu/docs/gcc/gcc_92.html

search

	Buy the book!

Using the GNU Compiler Collection (GCC)

6.1 Minimum and Maximum Operators in C++

It is very convenient to have operators which return the "minimum" or the "maximum" of two arguments. In GNU C++ (but not in GNU C),

a <? b

is the minimum, returning the smaller of the numeric values a and b;

a >? b

is the maximum, returning the larger of the numeric values a and b.

These operations are not primitive in ordinary C++, since you can use a macro to return the minimum of two things in C++, as in the following example.

#define MIN(X,Y) ((X) < (Y) ? : (X) : (Y))

You might then use `int min = MIN (i, j);' to set min to the minimum value of variables i and j.

However, side effects in X or Y may cause unintended behavior. For example, MIN (i++, j++) will fail, incrementing the smaller counter twice. The GNU C typeof extension allows you to write safe macros that avoid this kind of problem (see section 5.6 Referring to a Type with typeof). However, writing MIN and MAX as macros also forces you to use function-call notation for a fundamental arithmetic operation. Using GNU C++ extensions, you can write `int min = i <? j;' instead.

Since <? and >? are built into the compiler, they properly handle expressions with side-effects; `int min = i++ <? j++;' works correctly.