在C ++中将字符串声明为std：string [英] Declaring strings as std:string in C++

问题描述

这是基于GCC / G ++，通常在Ubuntu上。

下面是我完成的示例程序：

  #include< iostream> 
 
 using namespace std; 
 
 int main（）
 {
 
 std :: string c =Test; 
 cout<< C; 
 return 0; 
} 
  

上述代码可以正常工作。

但我有两个问题，我不太会得到...

1. std：string 也可以正常工作。有什么区别。




2. 如果我在类中使用 std :: string 变量，我得到一个错误错误：'std'不命名类型。此声明的示例：

  
 {
 private：
 std：string N; 
  

有人可以解释这些问题吗？
非常感谢！

解决方案

将字符串声明写为std：string也很好。有什么区别。

如果格式不同，区别会更清楚：

$ b b

  std：
 string c =Test; 
  

您正在宣告一个标签，名为 std ，并使用使用命名空间std; string c>。正确地写为 std :: string ，您使用中的 string

如果我使用 std :: string

$ c>在类中声明一个私有变量，我得到一个错误错误：'std'不命名一个类型。

< blockquote>

这是因为你不能把标签放在类定义中，只能在代码块中。你必须正确写入 std :: string 。 （如果类在头中定义，则 using namespace std 是一个比源文件更糟的主意，所以我敦促你不要这样做。）

此外，如果您使用 std :: string ，那么您应该 #include< ; string> 。看起来你的代码工作原理是由于< iostream> 拉入更多的定义比它需要，但你不能移植依赖。

This is based on GCC/G++ and usually on Ubuntu.

Here's my sample program I've done:

#include <iostream>

using namespace std;

int main()
{

std::string c = "Test";
cout << c;
return 0;
}

The above code works fine.

But I have two issues that I don't quite get...

1. Writing the string declaration as std:string also works fine. What's the difference.

2. If I use this std::string within a class to declare a private variable, I get an error error: ‘std’ does not name a type. Example of this declaration:

class KType
{
private:
  std:string N;

Can someone please explain these issues? Many thanks!

解决方案

Writing the string declaration as std:string also works fine. What's the difference.

The difference would be slight clearer if you formatted it differently:

std:
    string c = "Test";

You're declaring a label called std, and using the name string which has been dumped into the global namespace by using namespace std;. Writing it correctly as std::string, you're using the name string from the std namespace.

If I use this std::string within a class to declare a private variable, I get an error error: ‘std’ does not name a type.

That's because you can't put a label in a class definition, only in a code block. You'll have to write it correctly as std::string there. (If the class is defined in a header, then using namespace std is an even worse idea than in a source file, so I urge you not to do that.)

Also, if you're using std::string, then you should #include <string>. It looks like your code works by accident due to <iostream> pulling in more definitions than it need to, but you can't portably rely on that.

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