为什么const成员造成错误？
#include <vector>
class B {
};
class A {
const std::vector<B> m_v;
public:
A(const std::vector<B>& v) : m_v(v) {}
void doSomething() {}
};
void foo(void* bar) {
A* a = (A*)bar;
a->doSomething();
}
int main() {
std::vector<B> v;
std::vector<A > l;
for (auto i = 0; i < 10; i++) {
A a(v);
l.push_back(std::move(a));
foo((void*)&l[i]);
}
return 0;
}
$ g++ -Wall initList.cpp -o initList -lrt -O3 -std=c++0x
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/vector:70:0,
from initList.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc: In member function u2018void std::vector::_M_insert_aux(std::vector::iterator, _Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator, std::vector::iterator = __gnu_cxx::__normal_iterator >, typename std::_Vector_base::_Tp_alloc_type::pointer = A*]`:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:102:4: instantiated from u2018void std::vector::emplace_back(_Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_vector.h:840:9: instantiated from u2018void std::vector::push_back(std::vector::value_type&&) [with _Tp = A, _Alloc = std::allocator, std::vector::value_type = A]`
initList.cpp:23:27: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:319:4: error: use of deleted function '& A::operator=(const A&)`
initList.cpp:6:7: error: '& A::operator=(const A&)` is implicitly deleted because the default definition would be ill-formed:
initList.cpp:6:7: error: passing u2018const std::vector` as u2018this` argument of u2018std::vector& std::vector::operator=(const std::vector&) [with _Tp = B, _Alloc = std::allocator]` discards qualifiers [-fpermissive]
In file included from /usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/vector:61:0,
from initList.cpp:1:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h: In static member function u2018static _BI2 std::__copy_move_backward::__copy_move_b(_BI1, _BI1, _BI2) [with _BI1 = A*, _BI2 = A*]`:
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:581:18: instantiated from u2018_BI2 std::__copy_move_backward_a(_BI1, _BI1, _BI2) [with bool _IsMove = true, _BI1 = A*, _BI2 = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:590:34: instantiated from u2018_BI2 std::__copy_move_backward_a2(_BI1, _BI1, _BI2) [with bool _IsMove = true, _BI1 = A*, _BI2 = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:661:15: instantiated from u2018_BI2 std::move_backward(_BI1, _BI1, _BI2) [with _BI1 = A*, _BI2 = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:313:4: instantiated from u2018void std::vector::_M_insert_aux(std::vector::iterator, _Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator, std::vector::iterator = __gnu_cxx::__normal_iterator >, typename std::_Vector_base::_Tp_alloc_type::pointer = A*]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/vector.tcc:102:4: instantiated from u2018void std::vector::emplace_back(_Args&& ...) [with _Args = {A}, _Tp = A, _Alloc = std::allocator]`
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_vector.h:840:9: instantiated from u2018void std::vector::push_back(std::vector::value_type&&) [with _Tp = A, _Alloc = std::allocator, std::vector::value_type = A]`
initList.cpp:23:27: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.6.2/../../../../include/c++/4.6.2/bits/stl_algobase.h:546:6: error: use of deleted function '& A::operator=(const A&)`
如果我没有为m_v指定const。 它编译好。
这个错误提示了赋值运算符，我不知道它是如何被调用的。
任何想法？
提前致谢。
这是GCC / libstdc ++旧版本中的一个错误，你的代码可以用GCC 4.8.1编译。 现场示例 。 该错误是由触发
l.push_back(std::move(a));
因为较早版本的GCC试图在向量中创建一个默认构造的元素，并在第二步中将参数std::move(a)分配给它，而不是使用就地复制/移动ctor。
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