C++ std::map Initlializator 列表失败

Question

   std::map <ODParserETag ,std::function<void()>> procedure_map;

与

procedure_map = { {ODParserETag::ActorListETag, onUndefinedTag }, {ODParserETag::AdvancedWorkerETag, onUndefinedTag }, {ODParserETag::animationETag, onUndefinedTag }};

失败并出现错误:

/usr/include/c++/4.8/bits/stl_map.h:300:7: note:   no known conversion for argument 1 from ‘<brace-enclosed initializer list>’ to ‘std::initializer_list<std::pair<const ODParserETag, std::function<void()> > >’

并且 onU-T* 是无效的 ODParserXml::onUndefinedTag();

是否有任何 map 容器会为每个键返回一些默认预设值？ (如本例中的 onUndefinedTag() )...？

Answer 1

成员函数不是函数，因为您只能用对象调用它们。

一个捷径是使用 lambda 函数:

ODParserXml parser (...);
....

procedure_map[ODParserETag::ActorListETag] = [&] { parser.onUndefinedTag(); };

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另见

• https://stackoverflow.com/questions/5154116/stdfunction-to-member-function
• https://stackoverflow.com/questions/7582546/using-generic-stdfunction-objects-with-member-functions-in-one-class .

---

这是一些用于修补的代码(参见 http://ideone.com/iIEIiC ):

#include <iostream>
#include <map>
#include <functional>

int main() {
    std::map<int, std::function<void()>> funs;
    funs[0] = [] { std::cout << "0\n"; };
    funs[1] = [] { std::cout << "1\n"; };

    funs[0]();
    funs[1]();
    funs[0]();
    return 0;
}