Hi,

We are facing a problem when trying to delay load Qt DLLs into an application. See description below.

Best regards,
Antoine Trux
F-Secure

Environment
-----------
Windows XP, Visual Studio 2005.

Motivation for delay-loading Qt libraries
-----------------------------------------
We delay-load Qt libraries not for performance reasons, but in order to control the location from which they are loaded.

Description of the problem
--------------------------
Our project file (.pro) contains the following directive:
QMAKE_LFLAGS += /delayload:QtCored4.dll

If our code uses QVector's default constructor, e.g.:
QVector<int> foo;
then we get this linking error:
1>LINK : fatal error LNK1194: cannot delay-load 'QtCored4.dll' due to import of data symbol '"_declspec(dllimport) public: static struct QVectorData QVectorData::shared_null" (imp?shared_null@QVectorData@@2U1@A)'; link without /DELAYLOAD:QtCored4.dll

If our code uses QMap's default constructor, e.g.:
QMap<int, int> foo;
then we get this linking error:
1>LINK : fatal error LNK1194: cannot delay-load 'QtCored4.dll' due to import of data symbol '"_declspec(dllimport) public: static struct QMapData QMapData::shared_null" (imp?shared_null@QMapData@@2U1@A)'; link without /DELAYLOAD:QtCored4.dll

If our code uses QList's (or QStringList's) default constructor, e.g.:
QList<int > foo;
then we get this linking error:
1>LINK : fatal error LNK1194: cannot delay-load 'QtCored4.dll' due to import of data symbol '"_declspec(dllimport) public: static struct QListData::Data QListData::shared_null" (imp?shared_null@QListData@@2UData@1@A)'; link without /DELAYLOAD:QtCored4.dll

Possible workarounds for QVector and QMap
-----------------------------------------
For QVector, instead of:
QVector<int> foo;
writing:
QVector<int> foo(0); // 0 = initial size
solves the linking problem.

For QMap, instead of:
QMap<int, int> foo;
writing:
std::map<int, int> emptyMap;
QMap<int, int> map(emptyMap);
solves the linking problem.

No workarounds for QList
------------------------
For QList (or QStringList), we could not find any workaround. The reason is that QList has only two constructors:
1) QList() - the default constructor, which causes the linking problem
2) QList(const QList<T>& other) - the copy constructor; this would not cause a linking problem, but then, how to you construct `other' in the first place?

And trying to work around the problem by using QList's static functions:

• QList<T>::fromSet(const QSet<T>& set)
• QList<T>::fromStdList(const std::list<T>& list)
• QList<T>::fromVector(const QVector<T>& vector)
  does not work either, because all these function internally use QList's default constructor.