Mutation Survives When Comparing to Empty String in C++?

Question

I am mutating my code and it's complaining that the following mutation survived:

--- /home/user/src/file.cc 2019-12-03 13:48:12.510311
+++ /home/user/src/file.cc 2019-12-03 14:00:14.164006
@@ -283,7 +283,7 @@
 }

 bool SomeClass::isValid(proto::SomeProto const& task_pb) const {
-    if (task_pb.task_id() == "") {
+    if (task_pb.task_id() < "") {
         log(LOG_WARNING, "no id given");
         return false;
     } else if (task_pb.task_type() == proto::TaskType::UNKNOWN) {

The declaration for task_id() is:

const ::std::string& task_id() const;

Is there a string that can be less than ""? Would this even be considered a valid mutation for strings?

If `task_id` returns a `const char *`, this is technically valid, but pretty much nonsensical, C++. If `task_id` returns a `std::string`, one of the `<` overloads compares to a `std::string`, and `std::string` can be implicitly constructed from a string literal, so that's what gets compiled. — Sam Varshavchik, Dec 04 '19 at 16:22

score 0 · Accepted Answer · answered Dec 04 '19 at 16:41

0

std::string defines a lexicographic "less-than" relation, that can be accessed using operator<.

The specific expression you've shown will always evaluate to false, because no string sorts (lexicographically) less-than the empty string. But that doesn't make the code invalid, merely pointless. I don't know what you mean by a "valid mutation" exactly, but hopefully that will point you to the answer.

answered Dec 04 '19 at 16:41

Lightness Races in Orbit

378,754
76
643
1,055

A "valid mutation" would be a mutation that is actually testable. Could I come up with a test that provides some value that `task_id()` returns that would pass the existing code but not the mutated code. It sounds like no. Thanks for your answer. – Stephen Rasku Dec 04 '19 at 16:47
@StephenRasku The result will be the same for any non-empty `task_id()`, because the conditional assuredly evaluates to `false` in both cases. – Lightness Races in Orbit Dec 04 '19 at 16:49
That's what I thought. Thanks for the clarification. – Stephen Rasku Dec 04 '19 at 16:49
However, the behaviour differs for empty `task_id()`. – Lightness Races in Orbit Dec 04 '19 at 16:50

Mutation Survives When Comparing to Empty String in C++?

1 Answers1