为什么vector< bool> :: reference不返回bool的引用? [英] Why vector<bool>::reference doesn't return reference to bool?
问题描述
#include <vector>
struct A
{
void foo(){}
};
template< typename T >
void callIfToggled( bool v1, bool &v2, T & t )
{
if ( v1 != v2 )
{
v2 = v1;
t.foo();
}
}
int main()
{
std::vector< bool > v= { false, true, false };
const bool f = false;
A a;
callIfToggled( f, v[0], a );
callIfToggled( f, v[1], a );
callIfToggled( f, v[2], a );
}
上述示例的编译产生下一个错误:
The compilation of the example above produces next error :
dk2.cpp: In function 'int main()':
dk2.cpp:29:28: error: no matching function for call to 'callIfToggled(const bool&, std::vector<bool>::reference, A&)'
dk2.cpp:29:28: note: candidate is:
dk2.cpp:13:6: note: template<class T> void callIfToggled(bool, bool&, T&)
我使用g ++编译像这样:
I compiled using g++ (version 4.6.1) like this :
g++ -O3 -std=c++0x -Wall -Wextra -pedantic dk2.cpp
问题是为什么会发生这种情况? 向量< bool> :: reference
不是 bool&
?或者是编译器的错误?
或者,我试着做一些蠢事吗? :)
The question is why this happens? Is vector<bool>::reference
not bool&
? Or is it a compiler's bug?
Or, am I trying something stupid? :)
推荐答案
它被认为是std的一个错误。改用向量< char>
:
It is considered a mistake of the std. Use vector<char>
instead:
template<typename t>
struct foo {
using type = t;
};
template<>
struct foo<bool> {
using type = char;
};
template<typename t, typename... p>
using fixed_vector = std::vector<typename foo<t>::type, p...>;
有时您可能需要引用包含在矢量。不幸的是,使用向量< char>
只能提供chars的引用。如果您确实需要 bool&
,请查看 Boost Containers库。它有一个非特殊版本的向量< bool>
。
Occasionally you may need references to a bool contained inside the vector. Unfortunately, using vector<char>
can only give you references to chars. If you really need bool&
, check out the Boost Containers library. It has an unspecialized version of vector<bool>
.
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