字符数组作为C++映射中的值

Question

我想定义类似的东西

Map<int, char[5] > myMap;

上面的声明被c ++编译器接受,并且没有抛出错误,但是当我做这样的事情时

int main()
{
    char arr[5] ="sdf";
    map <int, char[5]> myMap;
    myMap.insert(pair<int, char[5]>(0,arr));
    return 0;
}

我得到错误:

In file included from /usr/include/c++/4.6/bits/stl_algobase.h:65:0,
                 from /usr/include/c++/4.6/bits/char_traits.h:41,
                 from /usr/include/c++/4.6/ios:41,
                 from /usr/include/c++/4.6/ostream:40,
                 from /usr/include/c++/4.6/iostream:40,
                 from charMap.cpp:1:
/usr/include/c++/4.6/bits/stl_pair.h: In constructor ‘std::pair<_T1, _T2>::pair(const _T1&, const _T2&) [with _T1 = int, _T2 = char [5]]’:
charMap.cpp:9:42:   instantiated from here
/usr/include/c++/4.6/bits/stl_pair.h:104:31: error: array used as initializer
/usr/include/c++/4.6/bits/stl_pair.h: In constructor ‘std::pair<_T1, _T2>::pair(const std::pair<_U1, _U2>&) [with _U1 = int, _U2 = char [5], _T1 = const int, _T2 = char [5]]’:
charMap.cpp:9:43:   instantiated from here
/usr/include/c++/4.6/bits/stl_pair.h:109:39: error: array used as initializer

对我来说,定义固定大小的字符数组非常重要,因为它可以优化我的网络流操作.有没有办法实现它？我不想用char *或std::string.

Answer 1

我理解你的性能要求(因为我也做类似的事情),但以这种方式使用字符数组是相当不安全的.

如果您可以访问C++ 11,则可以使用std::array.然后你可以定义你的地图,如:

map <int, array<char, 5>> myMap;

如果您不能使用C++ 11,那么您可以使用boost::array.

Answer 2

一种方法是将固定大小的字符数组包装为结构体。

struct FiveChar
{
   FiveChar(char in[5]) { memcpy(data, in, 5); }
   char& operator[](unsigned int idx) { return data[idx]; }
   char data[5];
};

int main(void)
{
   char arr[5] = "sdf";
   map<int, FiveChar> myMap;
   myMap.insert(pair<int, FiveChar>(0, arr));
   return 0;
}