如何解决无法编译:错误:''标记之前的预期主表达式
我无法获得此编译:
// main.cpp
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/composite_key.hpp>
#include <boost/multi_index/indexed_by.hpp>
#include <boost/multi_index/mem_fun.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/tag.hpp>
using namespace boost::multi_index;
struct by_attrs{};
// Generic MultiIndex that wraps boost::multi_index
template<typename Container>
class MultiIndex
{
public:
typedef typename Container::template index<by_attrs>::type::iterator attr_iterator;
template<typename FromArgs,typename ToArgs>
std::pair<attr_iterator,attr_iterator>
fetch_range(FromArgs&& from,ToArgs&& to)
const
{
return std::pair<attr_iterator,attr_iterator>(
_container.get<by_attrs>().lower_bound(from),_container.get<by_attrs>().upper_bound(to)
);
}
private:
Container _container;
};
class Foo
{
public:
int bar() const
{
return 1;
}
};
typedef multi_index_container<
Foo,indexed_by<
ordered_unique<
tag<by_attrs>,composite_key<
Foo,const_mem_fun<
Foo,int,&Foo::bar
>
>
>
>
> FooMultiIndexContainer;
typedef MultiIndex<FooMultiIndexContainer> FooMultiIndex;
int main()
{
FooMultiIndex foo_index;
}
错误(g++ -std=c++11 main.cpp
):
In member function 'std::pair<typename Container::index<by_attrs>::type::iterator,typename Container::index<by_attrs>::type::iterator> MultiIndex<Container>::fetch_range(FromArgs&&,ToArgs&&) const': main.cpp:28:55: error: expected primary-expression before '(' token 28 | return std::pair<attr_iterator,attr_iterator>(
解决方法
您需要在此处放置几个template
:
template<typename FromArgs,typename ToArgs>
std::pair<attr_iterator,attr_iterator>
fetch_range(FromArgs&& from,ToArgs&& to)
const
{
return std::pair<attr_iterator,attr_iterator>(
_container.template get<by_attrs>().lower_bound(from),_container.template get<by_attrs>().upper_bound(to)
);
}
您可能希望在所谓的相关上下文中使用typename
和template
来咨询该线程:Where and why do I have to put the “template” and “typename” keywords?
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