g ++ STL容器initializer_list在4.4和4.7之间的差异

Question

下面的C++ 0x/C++ 11特性（初始化器列表，包括STL容器）应该允许我在声明时初始化STL std::map。而且，它在g ++ 4.7.2中工作得很好，但是在g ++ 4.4.6中编译时出现错误。根据GCC文档，这个C++ 0x特性在4.4中可用，但很明显无论是（a）我做错了什么，或者（b）它在g ++ 4.4中是不完整的。

std::map<std::string,std::vector<std::string>> 
DbConnection::attrs_of_type = { 
    { "http",   { "url", "ipaddress", "port", 
          "username", "password" } }, 
    { "email",   { "address", "full_name" } }, 
    { "ftp",   { "hostname", "ipaddress", "port", 
          "username", "password", "filename" } } 
}; 

但是，当我尝试编译正在GCC 4.4.6，我得到以下no matching function call错误，在它的典型的“几乎无法理解”的方式：

database.cc:164: error: no matching function for call to ‘std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > > >::map(<brace-enclosed initializer list>)’ 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:195: note: candidates are: std::map<_Key, _Tp, _Compare, _Alloc>::map(std::initializer_list<std::pair<const _Key, _Tp> >, const _Compare&, const _Alloc&) [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >] 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:181: note:     std::map<_Key, _Tp, _Compare, _Alloc>::map(std::map<_Key, _Tp, _Compare, _Alloc>&&) [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >] 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:170: note:     std::map<_Key, _Tp, _Compare, _Alloc>::map(const std::map<_Key, _Tp, _Compare, _Alloc>&) [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >] 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:150: note:     std::map<_Key, _Tp, _Compare, _Alloc>::map() [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >] 

（有没有可能改变粘贴格式如何，所以它不需要尽可能多的水平滚动？）

无论如何。在这一点上，我试图弄清楚为了让这个初始化在g ++ 4.4.6中工作，我必须采取不同的措施。有什么我可以改变的方式我宣布std::map，或std::vector，这将解决问题？还是必须使用完全不同的方法，因为g ++ 4.4中的这个C++ 11特性的不同和/或不完整的实现？

Answer 1

您的代码是正确的。 g ++ - 4.4正式支持初始化列表。但我记得（我遵循wg21论文）有一个问题，特别是关于无法按照您在委托中某种程度上（与嵌套）的方式来初始化容器的问题。

由于这些更改是在以后完成的，很可能g ++ - 4.4没有完全支持std::initializer_list语法。