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c++gccwarningsgcc-warning

How do I best silence a warning about unused variables?


I have a cross platform application and in a few of my functions not all the values passed to functions are utilised. Hence I get a warning from GCC telling me that there are unused variables.

What would be the best way of coding around the warning?

An #ifdef around the function?

#ifdef _MSC_VER
void ProcessOps::sendToExternalApp(QString sAppName, QString sImagePath, qreal qrLeft, qreal qrTop, qreal qrWidth, qreal qrHeight)
#else
void ProcessOps::sendToExternalApp(QString sAppName, QString sImagePath, qreal /*qrLeft*/, qreal /*qrTop*/, qreal /*qrWidth*/, qreal /*qrHeight*/)
#endif
{

This is so ugly but seems like the way the compiler would prefer.

Or do I assign zero to the variable at the end of the function? (which I hate because it's altering something in the program flow to silence a compiler warning).

Is there a correct way?


Solution

  • You can put it in "(void)var;" expression (does nothing) so that a compiler sees it is used. This is portable between compilers.

    E.g.

    void foo(int param1, int param2)
    {
        (void)param2;
        bar(param1);
    }
    

    Or,

    #define UNUSED(expr) do { (void)(expr); } while (0)
    ...
    
    void foo(int param1, int param2)
    {
        UNUSED(param2);
        bar(param1);
    }