"Not all control paths return a value" when calling a function which throws [duplicate]

Question

Example:

int foo() { throw 0; }
int bar() { foo(); }

foo here doesn't get a warning, while bar gets the error "must return a value". More typically, bar would have some return statements and get the warning "not all control paths return a value".

Why isn't an indirect throw recognized as a proper way to exit the function? How can I work around it, ideally by modifying foo and not bar?

The actual example I have in mind is that I have a ThreadSafeExit function which calls the test platform's Exit function, and I hoped that adding throw 0 at the end would get rid of warnings.

There is a noreturn attribute for such purposes.

heap underrun
– heap underrun

2025-03-31 19:50:56 +00:00
Commented Mar 31, 2025 at 19:50 — heap underrun
– heap underrun, Commented Mar 31, 2025 at 19:50

Jeremy Richards · Accepted Answer · 2025-03-31 19:52:20Z

11

You should be able to quiet the compiler by applying the noreturn attribute to foo.

[[noreturn]]int foo() { throw 0; }
int bar() { foo(); }

However in this case, I would really fix it this way:

int foo() { throw 0; }
int bar() { return foo(); }

This will also make the compiler happy and is a lot more natural to read, since it is very common to invoke another function to calculate your return value. The first way can leave someone scratching their head as to what is going on if foo and bar are not close to each other in code.

You can do both, of course to be super clear about the intent.

answered Mar 31, 2025 at 19:52

Jeremy Richards

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6 Comments

user4581301 Over a year ago

How ever you go , I strongly recommend placing the return statement as the compiler isn't the only thing that will read the code. People will expect to see a return there, and there are few things more dangerous to code than a confused programmer.

Ted Lyngmo Over a year ago

@user4581301 The second option with return foo(); solves both silencing the warning and any user confusion that may arise I think.

user4581301 Over a year ago

@Ted my point is if there are two potential fixes, go with the one that doesn't <expletive deleted> with people's heads.

Ted Lyngmo Over a year ago

@user4581301 :-) That sounds like good advice. Going with both the attribute and the return would probably be the clearest and it may give the compiler the possibility to do some optimizations if the content of foo isn't seen in in bar's TU.

catnip Over a year ago

I think a return statement in bar is essential. Suppose someone makes a change to foo.

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