C++ Conditional Operator versus if-else

Question

I have always wondered about this. Let's say we have a variable, string weight, and an input variable, int mode, which can be 1 or 0.

Is there a clear benefit to using:

weight = (mode == 1) ? "mode:1" : "mode:0";

over

if(mode == 1)
    weight = "mode:1";
else
    weight = "mode:0";

beyond code readability? Are speeds at all affected, is this handled differently by the compiler (such as the ability of certain switch statements to be converted to jump tables)?

Answer 1

The key difference between the conditional operator and an if/else block is that the conditional operator is an expression, rather than a statement. Thus, there are few places you can use the conditional operator where you can't use an if/else. For example, initialization of constant objects, like so:

const double biasFactor = (x < 5) ? 2.5 : 6.432;

If you used if/else in this case, biasFactor would have to be non-const.

Additonally, constructor initializer lists call for expressions rather than statements as well:

X::X()
  : myData(x > 5 ? 0xCAFEBABE : OxDEADBEEF)
{
}

In this case, myData may not have any assignment operator or non-const member functions defined--its constructor may be the only way to pass any parameters to it.

Also, note that any expression can be turned into a statement by adding a semicolon at the end--the reverse is not true.