c++中删除迭代器指向的元素后，迭代器指向的被删除元素后面的元素

最新推荐文章于 2024-09-03 11:48:26 发布

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最新推荐文章于 2024-09-03 11:48:26 发布

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分类专栏： C++基础知识复习

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本文介绍了一种在C++中安全地从容器中移除过期元素的方法，并展示了如何正确遍历容器元素。通过使用迭代器并检查其有效性来避免常见的迭代器失效问题。

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1. C++向容器中插入和删除元素的时候，迭代器会失效，下面是正确删除容器元素的做法

void StatsServer::removeExpiredWorkers() {
  size_t expiredWorkerCount = 0;
  size_t expiredUserCount = 0;

  pthread_rwlock_wrlock(&rwlock_);  // write lock

  // delete all expired workers
  for (auto itr = workerSet_.begin(); itr != workerSet_.end(); ) {
    const int32_t userId   = itr->first.userId_;
    shared_ptr<WorkerShares> workerShare = itr->second;

    if (workerShare->isExpired()) {
      itr = workerSet_.erase(itr);

      expiredWorkerCount++;
      totalWorkerCount_--;
      userWorkerCount_[userId]--;
      
      if (userWorkerCount_[userId] <= 0) {
        userWorkerCount_.erase(userId);
      }
    } else {
      itr++;
    }
  }

  // delete all expired users
  for (auto itr = userSet_.begin(); itr != userSet_.end(); ) {
    shared_ptr<WorkerShares> workerShare = itr->second;

    if (workerShare->isExpired()) {
      itr = userSet_.erase(itr);

      expiredUserCount++;
      totalUserCount_--;
    } else {
      itr++;
    }
  }

  pthread_rwlock_unlock(&rwlock_);

  LOG(INFO) << "removed expired workers: " << expiredWorkerCount << ", users: " << expiredUserCount;
}

2. 遍历读取容器的元素的写法如下

for(auto itr = vec.begin(); itr != vec.end(); ++itr)
{
    read(*itr);
}