[英]Why am I getting compile error “use of deleted function 'std::unique_ptr …”
Am getting a huge compile error with message 我的消息收到了很大的编译错误
c:\mingw\include\c++\6.1.0\bits\predefined_ops.h:123:18: error: use of deleted function 'std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = Deduction; _Dp = std::default_delete<Deduction>]'
{ return bool(_M_comp(*__it1, *__it2)); }
when I pass a custom comparator to STL set_difference
function. 当我将自定义比较器传递给STL
set_difference
函数时。
My code: 我的代码:
struct Value{
std::string ded_code;
float amount;
Value(std::string code, float amt):ded_code(code), amount(amt){}
};
struct Deduction{
std::string p_number;
std::vector<std::unique_ptr<Value>> values;
Deduction(string pnum, string code, float amt):p_number(pnum){
auto val = std::make_unique<Value>(code, amt);
values.emplace_back(move(val));
}
};
class compute{
public:
vector<unique_ptr<Deduction>> deductions;
void fillDeductions(){
// fill deductions
...
}
};
class CompareDiff{
public:
bool operator()(unique_ptr<Deduction>& ded1, unique_ptr<Deductions>& ded2){
rPtr1 = ded1.get();
rPtr2 = ded2.get();
return ( rPtr1->p_number < rPtr2->p_number);
}
};
...
int main(){
...
// fill two deduction vectors
Compute compA = Compute()
compA.fillDeductions()
Compute compB = Compute()
compB.fillDeductions()
vector<unique_ptr<Deduction>> diffs
set_difference(compA.begin(), compA.end(),
compB.begin(), compB.end(),
inserter(diffs, diffs.begin()), CompareDiff());
}
Am using gcc 6.1.0 on windows 7 machine. 我在Windows 7机器上使用gcc 6.1.0。
What am I missing? 我错过了什么?
Regards. 问候。
PG PG
The chief feature of std::unqiue_ptr
is that it cannot be copied. std::unqiue_ptr
的主要特点是无法复制。 That's by design, and the name tells you as much. 这是设计,名称告诉你。
However, CompareDiff
tries to take its arguments by value. 但是,
CompareDiff
尝试按值获取其参数。 That requires a copy. 这需要一份副本。 Instead, take a
std::unique_ptr<..> const&
- no copy is needed. 相反,采用
std::unique_ptr<..> const&
- 不需要复制。
The reason why you are still getting an error: 你仍然得到一个错误的原因:
std::set_difference does copy internally: std :: set_difference在内部复制 :
Copies the elements from the sorted range [first1, last1) which are not found in the sorted range [first2, last2) to the range beginning at d_first.
将排序范围[first1,last1]中的元素(在排序范围[first2,last2]中找不到)复制到从d_first开始的范围。
http://en.cppreference.com/w/cpp/algorithm/set_difference http://en.cppreference.com/w/cpp/algorithm/set_difference
If you want your code to compile, use std::shared_ptr instead. 如果您希望编译代码,请改用std :: shared_ptr。
Keep in mind, that the Standard Library is optimized for Objects and not for pointers. 请记住,标准库是针对对象优化的,而不是针对指针的。 You will have to do the ownership management yourself if you use pointers.
如果使用指针,则必须自己进行所有权管理。
你不能复制构造unique_ptr
因为它是一个已删除的函数 ,你可以移动唯一的指针来转移所有权,但是你需要一个函子来比较你需要通过引用传递那些unique_ptr
的东西。
Use a unique_ptr<x>
to express that a function assumes ownership of an x
. 使用
unique_ptr<x>
表示函数承担x
所有权。
Use a shared_ptr<x>
to express that a function is part owner of an x
. 使用
shared_ptr<x>
表示函数是x
部分所有者。
If you indeed want to pass a unique_ptr
and transfer ownership, you should move
the smart pointer into the function argument. 如果您确实要传递
unique_ptr
并转移所有权,则应move
智能指针move
到函数参数中。
More notes on passing smart pointers , and Herb Sutter has some good thoughts in this CppCon talk . 关于传递智能指针的更多注释 ,Herb Sutter在这个CppCon讲话中有一些好的想法。
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