QMutex const/this conversion issue

mirswith

I am not sure what it is going on here, I have cleaned my project and I can't get this to go away in one of my classes. I have declared a private variable:

@
QMutex _listMutex;
@

And then I go to use it:

@
QMutexLocker lock(&_listMutex);
@

When I compile this one gives me:
@
SomeFile.cpp:111: error: C2664: 'QMutexLocker::QMutexLocker(QMutex *)' : cannot convert parameter 1 from 'const QMutex *' to 'QMutex *'
Conversion loses qualifiers
@

And elsewhere:

@
_listMutex.lock();
...
_listMutex.unlock();
@

and this gives me the compile errors:
@
SomeFile.cpp:289: error: C2662: 'QMutex::lock' : cannot convert 'this' pointer from 'const QMutex' to 'QMutex &'
Conversion loses qualifiers
SomeFile.cpp:291: error: C2662: 'QMutex::unlock' : cannot convert 'this' pointer from 'const QMutex' to 'QMutex &'
Conversion loses qualifiers
@

Yet I am using this exactly the same way in another class. What is going on?

Thanks.

baysmith

You are probably trying to lock/unlock the mutex inside a const member function. Since the lock/unlock functions on QMutex are non-const, the compiler complains. Change _listMutex to mutable.

@
mutable QMutex _listMutex;
@

dangelog

Can you pastebin the whole segment? Are you trying to lock a mutex that you have as member from a const method? (If so, use mutable).

mirswith

that was it. Just when one thinks they are getting the hang of const. :)

Thanks!

deimos

try declaring the mutex like

@mutable QMutex _listMutex;@

I am not sure, just a tought