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c++templateslanguage-lawyermember-variables

Suppress unused variable warning in C++ => Compiler bug or code bug?

Presently, I am using the following function template to suppress unused variable warnings:

template<typename T>
void
unused(T const &) {
  /* Do nothing. */
}

However, when porting to cygwin from Linux, I am now getting compiler errors on g++ 3.4.4 (On linux I am 3.4.6, so maybe this is a bug fix?):

Write.cpp: In member function `void* Write::initReadWrite()':
Write.cpp:516: error: invalid initialization of reference of type 'const volatile bool&' from expression of type 'volatile bool'
../../src/common/Assert.h:27: error: in passing argument 1 of `void unused(const T&) [with T = volatile bool]'
make[1]: *** [ARCH.cygwin/release/Write.o] Error 1

The argument to unused is a member variable declared as:

  volatile bool readWriteActivated;

Is this a compiler bug or a bug in my code?

Here is the minimal test case:

template<typename T>
void unused(T const &) { }

int main() {
  volatile bool x = false;
  unused(!x); // type of "!x" is bool
}
Solution

  • It is a compiler bug and there are no known work arounds:

    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42655

    It is fixed in v4.4.