Fix warnings unused but set variable

I fixed all warnings "-Wunused-but-set-variable" by gcc.

I added the attribute "DUNE_UNUSED" to the variables to avoid the warnings. 

But count is not unused. It is used in the assert a few lines below. Have a look at what assert actually is: count will be used when the preprocessor macro NDEBUG is not set. I suppose the correct fix here is to hide all uses of count behind #ifndef NDEBUG.

It seems that i misunderstood the meaning of DUNE_UNUSED. I used it to suppress compiler-warnings, that flag variables as "set but unused", but are not unused i.e. count in this case.

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"unused" is a bit of a bad attribute name. It means "This attribute, attached to a variable, means that the variable is meant to be possibly unused. GCC does not produce a warning for this variable." (from GCC); note the "possibly" before "unused".

The C++17 attribute has a better name: [[maybe_unused]]

So it is fine to apply it to variables that are only used in some configurations (like when building without -DNDEBUG). Though often one can just create the variable in configurations where it is also used; I find this the better solution.

No, you didn't misinterpret DNUE_UNUSED, but you misread the count variable. It is used, but only if you don't disable debugging using -DNDEBUG. Thus you can't mark it as unused, as it is used in certain configurations, but must hide it if NDEBUG is defined.

Now i see my mistake. That's the reason this warning only occurred in test "gcc-8-noassert". Thank you.

added 1 commit

• 9f22df14 - Fixed the warning regarding "count"

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We prefer to assign the variable in DUNE when defining it; i.e. just use

int count = vsprintf(buffer, format, args);

(This should probably also use vsnprintf but that is a seperate issue.)

changed this line in version 3 of the diff

added 1 commit

• e6069eda - Defined and initialized "count" in one line

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mentioned in commit 958ae1aa

merged