c++ - std::map - C++ 需要所有声明的类型说明符

Question

我正在尝试填充 std::map，但出现 2 个编译器错误，我不知道是什么原因。

std::map<std::string, std::string> dirFull;
dirFull["no"] = "north";
dirFull["so"] = "south";
dirFull["ea"] = "east";
dirFull["we"] = "west";
dirFull["nw"] = "north-west";
dirFull["ne"] = "north-east";
dirFull["sw"] = "south-west";
dirFull["se"] = "south-east";

这些是错误:

error: C++ requires a type specifier for all declarations
       dirFull["no"] = "north";
       ^
error: size of array has non-integer type 'const char[3]'
       dirFull["no"] = "north";
               ^~~~

---

我也试过这个:

std::map<std::string, std::string> dirFull = { 
    {"no", "north"}, {"so", "south"},
    {"ea", "east"}, {"we", "west"},
    {"ne", "north-east"}, {"nw", "north-west"}, 
    {"se", "south-east"}, {"sw","south-west"} };

这会导致完全不同类型的错误:

error: non-aggregate type 'std::map<std::string, std::string>' (aka '...') cannot be initialized with an initializer list 
std::map<std::string, std::string> dirFull = {
                                   ^         ~

Answer 1

您收到此错误是因为您试图在文件范围内执行语句。在函数中定义这些赋值，您将不会再遇到这些错误。

如果您想在静态初始化期间填充此map，您可以使用boost::assign 或constexpr 初始化语法来做到这一点。

//requires c++11:
const map <string,string> dirFull = {
    {"no",   "north"},
    {"so",   "south"},
    {"ea",   "east"},
    {"we",   "west"},
    {"nw",   "north-west"},
    {"ne",   "north-east"},
    {"sw",   "south-west"},
    {"se",   "south-east"},
};