错误：c++ [map] 没有命名类型

Question

我在文本冒险游戏的文本命令解析器中编写了以下内容。

我正在尝试将用户输入的字符串与枚举类中的项目相关联。以下是我的头文件：

#include <iostream>
#include <map>
#include <string>
using namespace std;

enum class Noun
{
    // Interrogation subjects
    name,                   // ask the subject his name
    base,                   // where is the base?
    attack,                 // when will the attack be?

    invalid
};

map < string, Noun > knownNouns;
knownNouns["name"]      = Noun::name;
knownNouns["base"]      = Noun::base;
knownNouns["attack"]    = Noun::attack;

Noun parseNoun(string &noun)
{
    auto n = knownNouns.find(noun);
    if ( n == knownNouns.end() ) {
        return Noun::invalid;
    }
    return n->second;

当我把它通过编译器时，我得到以下信息：

nouns.h:46:1: error: 'knownNouns' does not name a type
 knownNouns["name"]      = Noun::name;
 ^
nouns.h:47:1: error: 'knownNouns' does not name a type
 knownNouns["base"]      = Noun::base;
 ^
nouns.h:48:1: error: 'knownNouns' does not name a type
 knownNouns["attack"]    = Noun::attack;
 ^
nouns.h: In function 'Noun parseNoun(std::string&)':
nouns.h:52:10: error: 'n' does not name a type
     auto n = knownNouns.find(noun);
          ^
nouns.h:53:10: error: 'n' was not declared in this scope
     if ( n == knownNouns.end() ) {
          ^
nouns.h:54:16: error: 'Noun' is not a class or namespace
         return Noun::invalid;
                ^
nouns.h:56:12: error: 'n' was not declared in this scope
     return n->second;
            ^

这是我第一次尝试使用地图和枚举，我不确定我做错了什么。我也不是非常熟悉自动变量的使用，所以这对我来说有点像货物崇拜编程。我希望我理解了它的实现，一旦我解决了我遇到的类型定义问题，错误就会消失。

编辑：这很尴尬。我复制粘贴了一个我已经更正的错误。代码仍然无法编译时（即发生相同问题时）

map < string, Noun > knownNouns;
knownNouns["name"]      = Verb::name;
knownNouns["base"]      = Verb::base;
knownNouns["attack"]    = Verb::attack;

修正为

map < string, Noun > knownNouns;
knownNouns["name"]      = Noun::name;
knownNouns["base"]      = Noun::base;
knownNouns["attack"]    = Noun::attack;

Answer 1

您不能将非声明构造直接放在命名空间范围内。

C++ 翻译单元是一系列声明。

赋值等非声明语句必须在函数体内。

---

固定代码：

#include <iostream>
#include <map>
#include <string>
using namespace std;

enum class Noun
{
    // Interrogation subjects
    name,                   // ask the subject his name
    base,                   // where is the base?
    attack,                 // when will the attack be?

    invalid
};

map< string, Noun > knownNouns = 
{
    { "name", Noun::name },
    { "base", Noun::base },
    { "attack", Noun::attack }
};

auto parseNoun( string const& noun )
    -> Noun
{
    // auto n = knownNouns.find(noun);
    // if ( n == knownNouns.end() ) {
        // return Noun::invalid;
    // }
    // return n->second;
    return Noun::invalid;
}

这里knownNouns 已初始化。这不是作业，即使 = 看起来很像作业。

Answer 2

您不能像这样静态初始化地图条目：

 knownNouns["name"]      = Verb::name;
 knownNouns["base"]      = Verb::base;
 knownNouns["attack"]    = Verb::attack;