我如何返回一个std :: map，其中包含c ++中两个映射的差异? [英] How i can return a std::map containing the differences of two maps in c++?

问题描述

我有两张地图，我需要找到差异并创建仅具有差异的新地图.不确定如何执行此操作.我尝试使用set_difference，但并不太了解它是如何工作的.任何帮助，将不胜感激.谢谢

i have two maps and i need to find the differences and create a new map that only has the differences. Not sure how to do this. I tried using set_difference but don't really understand how it works. Any help would be appreciated. thanks

// header file
typedef std::map<std::string, int> MapCol;
typedef std::map<std::string, MapCol> MapRow;
MapRow m_mapRows;

//.cpp fle
CheckForDifferences( const Table& rhs )
{
    Table diffTable;
    vector<string> v;                           
    vector<string>::iterator it;
    it=set_difference (m_mapRows.begin(), m_mapRows.end(), diffTable.m_mapRows.begin(), diffTable.m_mapRows.end, v.begin());
}

std::set_difference( m_mapRows.begin(), m_mapRows.end(),
rhs.m_mapRows.begin(), rhs.m_mapRows.end(), diffTable.m_mapRows.begin());

好的，这是我尝试过的，但是我遇到了错误，第一个是 错误C2678:二进制'=':找不到运算符，该运算符采用类型为'const std :: string'的左侧操作数(或者没有可接受的转换)

ok this is what i tried, but i get errors, the first one being error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const std::string' (or there is no acceptable conversion)

有什么想法吗?

推荐答案

如果您有两个已排序的容器a和b，并且想要将不在一个容器中的对象集复制到另一个容器中c，您可以这样做:

If you have two sorted containers a and b and you want to copy the set of objects that aren't in either one into another container c, you'd do this:

std::set_symmetric_difference(
    a.begin(), a.end(),
    b.begin(), b.end(),
    std::back_inserter(c) );

如果只希望a中的元素不在b中，请使用set_difference而不是set_symmetric_difference.

If you just want the elements from a that aren't in b, use set_difference instead of set_symmetric_difference.

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