Qt-interest Archive, June 2007
Qt 4.3.0: Visual Studio level 4 warnings
Message 1 in thread
I'm compiling with Visual Studio 2002, using Qt 4.3.0.
With level 4 warnings turned on (/W4) I get 'warning C4127: conditional
expression is constant'.
For example:
c:\Qt\4.3.0\src\corelib\tools\qvector.h(407)
which is...
if (QTypeInfo<T>::isStatic) {
or
Qt\4.3.0\src\corelib\tools\qlist.h(331)
which is...
else if (QTypeInfo<T>::isComplex)
Why are these conditional expressions seen as constant?
Sam Dutton
SAM DUTTON
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Message 2 in thread
> With level 4 warnings turned on (/W4) I get 'warning C4127:
conditional
> expression is constant'.
>
> c:\Qt\4.3.0\src\corelib\tools\qvector.h(407)
>
> which is...
>
> if (QTypeInfo<T>::isStatic) {
>
> Why are these conditional expressions seen as constant?
because they *are* (at runtime).
Basically it means the trolls made the mistake to check for traits (like
::isStatic) with an if() at runtime, instead of using overloading to
check for it at compile time.
recommended reading:
Effective C++ Third Edition 55 Specific Ways to Improve Your Programs
and Designs By Scott Meyers, Addison Wesley Professional ISBN:
0-321-33487-6
The chapter "Item 47: Use traits classes for information about types"
handles exactly the problem.
Cheers,
Peter
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