[英]how do I use STL algorithms with a vector of pointers
I have a vector of pointers that are not owned by the container. 我有一个不是容器所有的指针向量。 How do I use algorithms on the targets of the pointers.
如何在指针的目标上使用算法。 I tried to use boost's ptr_vector, but it tries to delete the pointers when it goes out of scope.
我尝试使用boost的ptr_vector,但它会在超出范围时尝试删除指针。
Here is some code that needs to work: 以下是一些需要工作的代码:
vector<int*> myValues;
// ... myValues is populated
bool consistent = count(myValues.begin(), myValues.end(), myValues.front()) == myValues.size();
auto v = consistent ? myValues.front() : accumulate(myValues.begin(), myValues.end(), 0) / myValues.size();
fill(myValues.begin(), myValues.end(), v);
// etc.
I realize that for loops would work, but this happens in a bunch of places, so some kind of unary adapter? 我意识到for循环可以工作,但这发生在一堆地方,所以某种一元的适配器? I wasn't able to find one.
我找不到一个。 Thanks in advance!
提前致谢!
You could use Boost Indirect Iterator . 您可以使用Boost Indirect Iterator 。 When dereferenced (with
operator*()
), it applies an extra dereference, so you end up with the value pointed by the pointer referenced by the iterator. 取消引用时(使用
operator*()
),它会应用额外的解除引用,因此最终会得到迭代器引用的指针指向的值。 For more information, you can also see this question about a dereference iterator . 有关更多信息,您还可以查看有关取消引用迭代器的此问题 。
Here's a simple example: 这是一个简单的例子:
std::vector<int*> vec;
vec.push_back(new int(1));
vec.push_back(new int(2));
std::copy(boost::make_indirect_iterator(vec.begin()),
boost::make_indirect_iterator(vec.end()),
std::ostream_iterator<int>(std::cout, " ")); // Prints 1 2
bool consistent = count_if(myValues.begin(), myValues.end(),
bind2nd(ptr_fun(compare_ptr), *myValues.front())) == myValues.size();
int v = consistent ? *myValues.front() : accumulate(
myValues.begin(), myValues.end(), 0, sum_int_ptr) / myValues.size();
for_each(myValues.begin(), myValues.end(), bind1st(ptr_fun(assign_ptr),v));
Fill can't take assign function (so that it would dereference pointers). 填充不能采用赋值函数(因此它会取消引用指针)。 Therefore for_each() was used.
因此使用了for_each()。 For optimization it would be wise to add if(!consistent) before running for_each().
为了优化,在运行for_each()之前添加if(!consistent)是明智的。 Functions used in above STL one liners:
以上STL一个衬里使用的功能:
int sum_int_ptr(int total, int * a) { return total + *a; }
void assign_ptr(int v, int *ptr) { *ptr = v; }
bool compare_ptr(int* a, int pattern) { return *a == pattern; }
You can look at boost::shared_ptr<>
- a smart pointer with reference counting. 您可以查看
boost::shared_ptr<>
- 一个带引用计数的智能指针。 It will not delete the pointer after it goes out of scope. 它超出范围后不会删除指针。
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