重载运算符<<为字符串工作

发布于 2024-09-10 07:13:59 字数 661 浏览 4 评论 0 原文

在以下代码中：

 using namespace std;

 //ostream& operator<< (ostream& out,const string & str)
 //{    
 //  out << str.c_str();    
 //  return out; 
 //}

 int _tmain(int argc, _TCHAR* argv[])
 {

     ofstream file("file.out");  

     vector<string> test(2); 

     test[0] = "str1"; 
     test[1] = "str2";
     ostream_iterator<string> sIt(file);

     copy(test.begin(), test.end(), sIt);

     file.close();
    return 0;
}

重载 operator << 的正确方法是什么 copy(test.begin(), test.end(), sIt); 工作。

我缺少什么？

编辑：我只是愚蠢......忘记包含“字符串”标题

谢谢！

原文

In the following code:

 using namespace std;

 //ostream& operator<< (ostream& out,const string & str)
 //{    
 //  out << str.c_str();    
 //  return out; 
 //}

 int _tmain(int argc, _TCHAR* argv[])
 {

     ofstream file("file.out");  

     vector<string> test(2); 

     test[0] = "str1"; 
     test[1] = "str2";
     ostream_iterator<string> sIt(file);

     copy(test.begin(), test.end(), sIt);

     file.close();
    return 0;
}

what is the proper way to overload operator << to make
copy(test.begin(), test.end(), sIt); work.

What am I missing?

EDIT: I'm just stupid... forgot to include "string" header

Thank you!

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倚栏听风 2024-09-17 07:13:59

您不需要重载operator<<来处理字符串，它已经知道如何处理它们。

std::copy( test.begin(), test.end(), 
           std::ostream_iterator<std::string>( file, "\n" ) );

将产生：

str1
str2

您想在那里做一些不同/特别的事情吗？

You do not need to overload operator<< to work with strings, it already knows how to handle them.

std::copy( test.begin(), test.end(), 
           std::ostream_iterator<std::string>( file, "\n" ) );

will produce:

str1
str2

Is there anything different/special that you want to be done there?

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ˉ厌 2024-09-17 07:13:59

正如 David 已经指出的那样，已经有一个用于字符串的运算符<<，因此您不必提供一个。如果您真的想定义自己的重载，那么就会有一个小问题，因为实际上您不允许这样做。 operator<< 是在 std 命名空间中定义的，因此如果您希望为 std::string （中的版本）提供可用的重载，大多数实现都是模板函数，因此存在潜在的重载），您也必须在 std 命名空间中执行此操作（这是因为歧义和重载的方式）已在 C++ 中解决，这里有一些注意事项）。例如：

namespace std {
 ostream& operator<< (ostream& out,const string & str)
  {     
    out << "A STRINGY:" << str.c_str();     
    return out; 
  }
}

但是，普通用户不允许向 std 命名空间添加内容，因为它可能会产生不可预见的特定于实现的影响，并且可能会破坏标准库内的各种内容。另外，不能保证您的标准库实现具有可重载运算符<<。这意味着，它可能有效，也可能无效。

As David already pointed out, there is already a operator<< for strings, so you don't have to provide one. Should you really want to define your own overload anyway, then there's a slight problem, because actually you are not allowed to do that. operator<< is defined in the std namespace, so if you want to have a usable overload for std::string (the version in most implementations is a template function, so there is a potential overload), you'll have to do this in the std namespace too (this because of the ways ambiguities and overloads are resolved in C++, there are some caveats here) . For example:

namespace std {
 ostream& operator<< (ostream& out,const string & str)
  {     
    out << "A STRINGY:" << str.c_str();     
    return out; 
  }
}

However, adding stuff into the std namespace is not allowed for ordinary users, because it might have implementation specific effects that are unforeseeable and could break all kinds of stuff inside the standard library. Also, there is no guarantee, that your implementation of the standard library has a overloadable operator<<. This means, it could work or it could not.

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