类中的 C++ 字符串
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C++ string in classes
提问by Kim Gr?sman
I know this is quite a ridiculous question but this is quite confusing and irritating, as something that shouldwork simply is not. I'm using Code Blocks with the GCC compiler and I am trying to simply create a string variable in my class
我知道这是一个非常荒谬的问题，但这是非常令人困惑和恼人的，因为本来应该起作用的东西却没有。我在 GCC 编译器中使用代码块，我试图在我的类中简单地创建一个字符串变量
#ifndef ALIEN_LANGUAGE
#define ALIEN_LANGUAGE
#include <string>
class Language
{
public:
private:
string str;
};
#endif
Strange enough, my compiler halts me with an error saying this:
奇怪的是，我的编译器以这样的错误阻止了我：
C:\Documents and Settings\...|11|error: `string' does not name a type|
||=== Build finished: 1 errors, 0 warnings ===|
For some reason, it is unable to find the class "string" which for some reason, my main.cpp is able to detect "#include " while my language class is not able for some reason.
出于某种原因，它无法找到类“string”，出于某种原因，我的 main.cpp 能够检测到“#include”，而我的语言类由于某种原因无法检测到。
This is the main I wrote quickly just to see it main itself is able to see the string file:
这是我快速写的 main 只是为了看到它 main 本身能够看到字符串文件：
//main.cpp
#include <iostream>
#include <string>
#include "alien_language.h"
using namespace std;
int main()
{
string str;
return 0;
}
Does anyone know what's going on?
有谁知道发生了什么？
回答by GManNickG
using namespace std;
using namespace std;
That's what's going on.
这就是正在发生的事情。
You don't have std::prefixing the string in your class. Everything in the standard library is in the namespace std.
您没有std::在类中为字符串添加前缀。标准库中的所有内容都在命名空间中std。
It is generally regarded as bad practice to use using namespace std;, by the way. For more information on why and what to do instead, check out this question: Using std Namespace.
using namespace std;顺便说一句，通常认为使用 是不好的做法。有关原因和操作的更多信息，请查看此问题：使用 std 命名空间。
回答by Ropez
The string class is defined in the std namespace. You should chenge the class to this:
字符串类在 std 命名空间中定义。你应该把班级改成这样：
class Language
{
public:
private:
std::string str;
};
It is also possible, but not recommended to add this to the top of the header file:
也可以，但不建议将其添加到头文件的顶部：
using namespace std;
回答by Kim Gr?sman
string is in namespace std, and you need to qualify it fully inside your header file:
字符串在命名空间 std 中，您需要在头文件中完全限定它：
#include <string>
class Language
{
public:
private:
std::string str;
};
Do not use using namespace std;or similar in header files.
不要using namespace std;在头文件中使用或类似。
回答by Silfverstrom
You should refer to it as std::string;
您应该将其称为 std::string;
回答by Twisol
It looks to me like you're missing the all-important (with a hint of sarcasm) using namespace std;line. Either add that in before your class, or explicitely use std::string str. I'd recommend against adding the using namespace std;line in a header file, as it would pollute the mainspace for any file that includes it.
在我看来，您似乎错过了最重要的（带有一丝讽刺意味）的using namespace std;台词。要么在您的课程之前添加它，要么明确使用std::string str. 我建议不要using namespace std;在头文件中添加该行，因为它会污染包含它的任何文件的主空间。
回答by Abhay
The stringclass in standard C++ is in stdnamespace. Write something like
using std::string;in your header or fully qualify it as std::string in your header.
string标准 C++ 中的类位于std命名空间中。using std::string;在你的标题中写一些类似的东西或者
在你的标题中将它完全限定为 std::string 。
Beware that using namespace std;in header is a bad practice (read here).
请注意，using namespace std;在标题中是一种不好的做法（请阅读此处）。
