调用map :: count用空的weak_ptr作为参数安全吗？ [英] Is calling map::count with an empty weak_ptr as argument safe?

问题描述

可以安全地 map :: count 在未初始化的空值 weak_ptr 安全？

我仍然没有经验的c ++，没有技巧来确定这个。 p>

在我的应用程序中，一个 weak_ptr 正被保留在地图中的关键字并且必须首先被值找到。如果找不到，未初始化的 weak_ptr 是 return ed，并在 map ::计数。

代码

设置

  map< my_ptr，connection_data，owner_less< my_ptr>> m_connections; 
 typedef map< my_ptr，connection_data，owner_less< my_ptr>> :: iterator it; 
  

按资料查找

  my_ptr get_my_ptr_from_data（string data）{
 my_ptr my_ptr_to_send; 
 for（it iterator = my_ptrs.begin（）; iterator！= my_ptrs.end（）; iterator ++）{
 if（iterator-> second.data == data）{
 my_ptr_to_send = iterator-> first; 
 break; 
} 
} 
 return my_ptr_to_send; 
} 
  

查找

  my_ptr found_ptr = get_my_ptr_from_data（data）; 
 if（my_ptrs.count（found_ptr））{
  

解决方案

可以安全地调用 find （和 count ），只要你定义的任何订单都不会t依赖指针是非空的。 找到（和 count ）的唯一的事情是使用参数作为比较器的参数。

但是，使用 weak_ptr 作为关联容器中的键是不安全的。如果它过期，那么容器的顺序是破碎的，以后尝试使用容器会给出不明确的行为。

Is it safe to call map::count on an uninitialized thus empty weak_ptr safe?

I'm still very inexperienced with c++ and do not have the skills to determine this.

In my application, a weak_ptr is being held as key in a map and must be found first by the values. If it cannot be found, an uninitialized weak_ptr is returned and used in map::count.

Code

Setup

map<my_ptr, connection_data, owner_less<my_ptr>> m_connections;
typedef map<my_ptr, connection_data, owner_less<my_ptr>>::iterator it;

Find by data

my_ptr get_my_ptr_from_data(string data){
    my_ptr my_ptr_to_send;
    for(it iterator = my_ptrs.begin(); iterator != my_ptrs.end(); iterator++) {
        if(iterator->second.data == data){
            my_ptr_to_send = iterator->first;
            break;
        }
    }
    return my_ptr_to_send;
}

Finding

my_ptr found_ptr = get_my_ptr_from_data(data);
if(my_ptrs.count(found_ptr) ){

解决方案

It's safe to call find (and count), as long as whatever ordering you've defined doesn't rely on the pointer being non-empty. The only thing that find (and count) will do with the argument is use it as an argument for the comparator.

However, it's not safe to use weak_ptr as a key in an associative container. If it expires, then the container's order is broken, and trying to use the container afterwards will give undefined behaviour.

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