c++ - 无法在 Visual Studio 2015 中将 typedef 转换为 std::pair

Question

我尝试将一些项目从 Visual Studio 2010 升级到 2015。在 2010 中，一切正常，但在 2015 中，我遇到了我不太理解的编译器错误。

我将代码压缩成一个 SSCCE

#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <vector>
#include <ctime>
#include <cstdlib>
#include <string>
#include <sstream>

#define UNUSED(x) (void(x))

class ColumnDef
{
public:
};

class XMLColumnDef
{
public:
    typedef std::pair<std::string, XMLColumnDef> pair;
    typedef std::pair<std::string, XMLColumnDef *> ptr_pair;

public:
    // Move constructor for moving the column into an container
    // without destroying it. Note that the source is no longer valid after 
    // such a move.
    XMLColumnDef(XMLColumnDef &oSource)
    {
        mColumn = oSource.mColumn;
        oSource.mColumn = NULL;
    }

    XMLColumnDef(ColumnDef *pColumn)
    {
        mColumn = pColumn;
    }

    virtual ~XMLColumnDef(void)
    {
        delete mColumn;
    }

private:
    ColumnDef *mColumn;
};

class XMLNodeObserver
{
public:
    typedef std::map<std::string, XMLNodeObserver *> map;
    typedef std::pair<std::string, XMLNodeObserver *> pair;
    typedef std::map<std::string, XMLColumnDef> row_def;

public:
    XMLNodeObserver(void) {}
    virtual ~XMLNodeObserver(void) {};

    void addObserver(XMLNodeObserver::map &oNodeObserver, std::string const &oPath, XMLNodeObserver *oObserver = NULL)
    {
        UNUSED(oNodeObserver);
        UNUSED(oPath);
        UNUSED(oObserver);
    }
    void addColumnDef(XMLNodeObserver::map &oNodeObserver, std::string const &oPath, ColumnDef *oColumn, XMLNodeObserver *oObserver = NULL)
    {
        if (oObserver == NULL)
            oObserver = this;

        addObserver(oNodeObserver, oPath, oObserver);

        XMLColumnDef::pair pr = std::make_pair(oPath, XMLColumnDef(oColumn));

        if (oObserver->mColumnDefs.find(oPath) != oObserver->mColumnDefs.end())
        {
            // If a node already exists, we report an internal error, because this indicates a program bug and should be fixed.
            std::cerr << "INTERNAL ERROR: Duplicate rowdef key in XML node observer: " << oPath << std::endl;
        }
        oObserver->mColumnDefs.insert(pr);
    }

private:
    row_def mColumnDefs;
    bool mDebugMode;
};

int main()
{
    XMLNodeObserver o;
    XMLNodeObserver::map om;

    o.addColumnDef(om, "/testpath", new ColumnDef());

    std::cout << "\nDone! Press any key..." << std::endl;
    std::cin.ignore();

    return 0;
}

我在这一行中得到的错误:

oObserver->mColumnDefs.insert(pr);

我得到的错误是这样的:

junk.cpp(104): error C2664: 'void std::_Tree<std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,false>>::insert(std::initializer_list<std::pair<const _Kty,_Ty>>)': cannot convert argument 1 from 'XMLColumnDef::pair' to 'std::pair<const _Kty,_Ty> &&'
          with
          [
              _Kty=std::string,
              _Ty=XMLColumnDef,
              _Pr=std::less<std::string>,
              _Alloc=std::allocator<std::pair<const std::string,XMLColumnDef>>
          ]
          and
          [
              _Kty=std::string,
              _Ty=XMLColumnDef
          ]
junk.cpp(104): note: Reason: cannot convert from 'XMLColumnDef::pair' to 'std::pair<const _Kty,_Ty>'
          with
          [
              _Kty=std::string,
              _Ty=XMLColumnDef
          ]
junk.cpp(104): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

看起来 Visual Studio 2015 不喜欢参数 oPath 是 const & 但这不重要，因为它应该分配给 pair 成员。

我还删除了 typedefs 并尝试使用长名称对其进行编译，但这似乎不是问题所在(无论如何也不应该)，因为我遇到了同样的错误。

喜欢:

std::pair<std::string, XMLColumnDef> pr = std::pair<std::string, XMLColumnDef>(oPath, XMLColumnDef(oColumn));

Answer 1

map 中的对类型为 pair<const key,value>而不是 pair<key,value> .尝试使用 MyMapType::value_type typedef 代替。您可以免费获得它!

例子:

typedef std::map<std::string, XMLNodeObserver *> MyMapType;
typedef MyMapType::value_type MyPairType;