Strange C++ syntax?

Question

This may be a stupid question but I have a code with the following line:

Solver *S, *STP = S = 
UseDummySolver ? createDummySolver() : new STPSolver(true);

I know the ternary operator but it's the equals signs that confuse me a bit. Can anyone give me some explanation ? Thanks.

Answer 1

Written out, it's

Solver *S;
Solver *STP;
S = UseDummySolver ? createDummySolver() : new STPSolver(true);
STP = S;

It's very ugly though, I'd not recommend doing that in your code.

The recommended way would be to write it as follows (use initialization, rather than assignment):

Solver *S = UseDummySolver ? createDummySolver() : new STPSolver(true);
Solver *STP = S;

Answer 2

I would recommend this:

Solver *S = UseDummySolver ? createDummySolver() : new STPSolver(true);
Solver *STP = S;

It is concise, yet neat and clean.

Also, it uses initialization, rather than assignment. You should prefer initialization over assignment wherever possible.

Answer 3

You're looking at chained assignment.

It is the same as:

Solver *S;
Solver *STP;
S = UseDummySolver ? createDummySolver() : new STPSolver(true);
STP = S;