Qt Throwing Illegal Error at QVariant - c++

Question

I have some code that is meant to get a QList of QMaps from a set of data. Then it should go through all the QMaps in that list. For some reason upon attempting this I am getting some errors regarding the QVector used to store data. Here is my code:
#include <QCoreApplication>
#include <QMap>
#include <QVariant>
#include <QDebug>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QList<QMap<QString, QVariant>> maps;
QMap<QString, QVariant> item1;
item1.insert("Item 1", QVariant::fromValue(1));
maps.append(item1);
foreach (const QMap<QString, QVariant> & map, maps)
{
qDebug() << map;
}
return a.exec();
}
Error:
..\ErrorTest\main.cpp(17): warning C4002: too many actual parameters for macro 'Q_FOREACH'
..\ErrorTest\main.cpp(17): error C2275: 'QVariant': illegal use of this type as an expression
C:\Qt\5.8\msvc2015_64\include\QtCore/qsharedpointer_impl.h(94): note: see declaration of 'QVariant'
..\ErrorTest\main.cpp(17): error C2955: 'std::remove_reference': use of class template requires template argument list
D:\Microsoft Visual Studio 14.0\VC\INCLUDE\xtr1common(301): note: see declaration of 'std::remove_reference'
..\ErrorTest\main.cpp(17): error C2065: 'map': undeclared identifier
..\ErrorTest\main.cpp(17): error C2143: syntax error: missing ')' before '>'
..\ErrorTest\main.cpp(17): error C2059: syntax error: '>'
..\ErrorTest\main.cpp(17): error C2065: '_container_': undeclared identifier
..\ErrorTest\main.cpp(17): error C2228: left of '.control' must have class/struct/union
..\ErrorTest\main.cpp(17): note: type is 'unknown-type'
..\ErrorTest\main.cpp(17): error C2228: left of '.i' must have class/struct/union
..\ErrorTest\main.cpp(17): note: type is 'unknown-type'
..\ErrorTest\main.cpp(17): error C2228: left of '.e' must have class/struct/union
..\ErrorTest\main.cpp(17): note: type is 'unknown-type'
..\ErrorTest\main.cpp(17): error C2059: syntax error: ')'
..\ErrorTest\main.cpp(17): error C2143: syntax error: missing ';' before 'for'
..\ErrorTest\main.cpp(17): error C2059: syntax error: '='
..\ErrorTest\main.cpp(17): error C2143: syntax error: missing ';' before '}'
..\ErrorTest\main.cpp(17): fatal error C1004: unexpected end-of-file found
Thank you, and yes the tagData->toMappedList() returns the correct set of QMaps/data.

Answer 1

Imho the problem is the , inside the template. Sadly foreach is nothing but a call for Q_FOREACH which is a macro. It requires to arguments separated by comma. But because of the template you have 2 commas. I had this problem a while ago, though Qt Creator at least provided me with error: macro "Q_FOREACH" passed 3 arguments, but takes just 2 instead of the ton of errors you got. In your case this would be:
..\ErrorTest\main.cpp(17): warning C4002: too many actual parameters for macro 'Q_FOREACH'
I would suggest a for loop with an iterator to traverse the list of maps. Unless you want to dump the const in which case you can do:
QMap<QString, QVariant> map;
foreach (map, maps) {
...
}
You can also use auto but again - no constantness.
If constantness is a critical aspect in your case, go for the for loop with a constant iterator.