Question

我在shared_ptr向量中找到一个元素时遇到了一些问题。

以下是我最终的结果：

std::vector<std::shared_ptr<Block>> blocks;

bool contains(Block* block) {
  for (auto i = blocks.begin(); i != blocks.end(); ++i) {
    if ((*i).get() == block) {
      return true;
    }
  }
  return false;
}

但是，我没有设法使用std::find甚至std::find_if。是否有更符合c ++标准的方法来实现这一目标？

编辑：这是我在回答后的代码：

bool contains(Block* block) {
  auto found = std::find_if(blocks.begin(), blocks.end(), [block](std::shared_ptr<Block> const& i){
    return i.get() == block;
  });
  return found != blocks.end();
}

Answer 1

尝试：

std::find_if(blocks.begin(), blocks.end(), 
  [block](std::shared_ptr<Block> const& i){ return i.get() == block; });

Answer 2

更简单：

bool contains(Block* block) {
  return std::any_of(blocks.cbegin(), blocks.cend(),
                     [block](std::shared_ptr<Block> const& i) { return i.get() == block; });
}

Answer 3

根据其他人的回答和评论，以下是来自ideone的完整工作样本：

#include <vector>
#include <memory>
#include <algorithm>
#include <iostream>

using namespace std;

struct Block
{
    bool in_container(const vector<shared_ptr<Block>>& blocks)
    {
        auto end = blocks.end();
        return end != find_if(blocks.begin(), end,
                              [this](shared_ptr<Block> const& i)
                                  { return i.get() == this; });
    }
};

int main()
{
    auto block1 = make_shared<Block>();
    auto block2 = make_shared<Block>();

    vector<shared_ptr<Block>> blocks;
    blocks.push_back(block1);

    block1->in_container(blocks) ?
        cout << "block1 is in the container\n" :
        cout << "block1 is not in the container\n";

    block2->in_container(blocks) ?
        cout << "block2 is in the container\n" :
        cout << "block2 is not in the container\n";

    return 0;
}

这是输出：

block1 is in the container
block2 is not in the container

在shared_ptr容器中查找元素？

3 个答案: