是否可以在自己的模板类中使用QMultiMap::ConstIterator ?
Is it possible to use to use QMultiMap::ConstIterator in own template class?
我想使用
迭代QMultiMap
QMultiMap<double, TSortable>::const_iterator it;`
但是编译器报错
error: expected ‘;’ before ‘it’
导致
error: ‘it’ was not declared in this scope
用于每次使用。我尝试了ConstIterator
, const_iterator
,甚至较慢的Iterator
,没有任何成功。它甚至可以使用Q(多)地图与模板类?为什么我不能声明一个迭代器当定义(作为void*)是ok的?
我使用以下代码(省略了包含保护):
#include <QtCore/QDebug>
#include <QtCore/QMap>
#include <QtCore/QMultiMap>
#include <limits>
/** TSortable has to implement minDistance() and maxDistance() */
template<class TSortable>
class PriorityQueue {
public:
PriorityQueue(int limitTopCount)
: limitTopCount_(limitTopCount), actMaxLimit_(std::numeric_limits<double>::max())
{
}
virtual ~PriorityQueue(){}
private:
void updateActMaxLimit(){
if(maxMap_.count() < limitTopCount_){
// if there are not enogh members, there is no upper limit for insert
actMaxLimit_ = std::numeric_limits<double>::max();
return;
}
// determine new max limit
QMultiMap<double, TSortable>::const_iterator it;
it = maxMap_.constBegin();
int act = 0;
while(act!=limitTopCount_){
++it;// forward to kMax
}
actMaxLimit_ = it.key();
}
const int limitTopCount_;
double actMaxLimit_;
QMultiMap<double, TSortable> maxMap_;// key=maxDistance
};
GCC在你引用的错误之前给出这个错误:
error: need ‘typename’ before ‘QMultiMap<double, TSortable>::const_iterator’ because ‘QMultiMap<double, TSortable>’ is a dependent scope
解释了这个问题。添加typename
关键字:
typename QMultiMap<double, TSortable>::const_iterator it;
,它会生成