将NSDictionary转换为std :: vector [英] Convert NSDictionary to std::vector

问题描述

我想将NSDictionary映射为浮点值的整数转换为C ++ std :: vector，其中原始NSDictionary的键为向量的索引.

I want to convert an NSDictionary mapping integers to floating point values into a C++ std::vector where the key from the original NSDictionary is the index into the vector.

我有一些我认为可以使用的代码，但似乎创建的矢量大于字典中键-值对的数量.我想这与我索引到向量的方式有关.

I have code that I thought would work, but it seems to create a vector larger than the number of key-value pairs in the dictionary. I'm guessing its something to do with the way I am indexing into the vector.

任何帮助都将不胜感激.

Any help greatly appreciated.

这是我的代码:

 static std::vector<float> convert(NSDictionary* dictionary)
  {
      std::vector<float> result(16);
      NSArray* keys = [dictionary allKeys];
      for(id key in keys)
      {        
          id value = [dictionary objectForKey: key];
          float fValue = [value floatValue];
          int index = [key intValue];
          result.insert(result.begin() + index, fValue);
      }
      return result;
  }

推荐答案

使用数字初始化向量会创建很多条目.在这种情况下，向量将以16个元素开始，并且每个插入将添加元素，因此最终将以16 + N 个元素

Initialising a vector with a number creates that many entries to begin with. In this case, your vector will start with 16 elements, and each insert will add elements, so you'll end up with 16 + N elements.

如果要将元素更改为新值，只需为其分配.不要使用插入:

If you want to change an element to a new value simply assign to it. Don't use insert:

result[index] = fValue;

但是，您实际上应该只使用map<int, float>:

However, you really should just use map<int, float>:

std::map<int, float> result;
NSArray* keys = [dictionary allKeys];
for(id key in keys)
{        
    id value = [dictionary objectForKey: key];
    float fValue = [value floatValue];
    int index = [key intValue];
    result[index] = fValue;
}

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