如何创建如std :: cout的功能？ [英] How to create functions like std::cout?

问题描述

我为我的项目创建了自己的日志库，我想创建一个函数，如iostream的std :: cout，日志到一个文件，并打印到控制台。

这里是我想要的：

  enum 
 {
 debug，error，warning，info 
}; 
 
 LOG（level）<< 测试; // level  - 从上面的枚举
  

EDIT：像这样：

  int iPlayerID = 1337; 
 LOG（info）<< Player< iPlayerID<< 连接的; 
  

[Thu Jan 29 18:32:11 2015] 1337已连接

解决方案

std :: cout 不是一个函数，它是一个类型 std :: ostream 的对象，它重载运算符<< p>

您可以如何做的快速草图：

 枚举级别{ 
 debug，error，warning，info 
}; 
 
 struct Logger {
 std :: ostream * stream; //在构造函数中设置此值，将
 //指向文件或控制台流
级别debug_level; 
 public：
 Logger& operator<<（const std :: string& msg）
 {
 * stream< msg; //也打印级别等。
 return * this; 
} 
 
朋友Logger& log（Logger& logger，Level n）; 
 {
 logger.debug_level = n; 
 return logger; 
} 
}; 
  

Ant然后使用

  Logger l; 
 log（l，debug）<< 测试; 
  

I'm creating my own logging library for my project, I Want to create a function like iostream's std::cout, to log to a file and print to console also.

Here's what i want:

enum
{
    debug, error, warning, info
};

LOG(level) << "test"; // level - from the above enum

EDIT: The Result must be like this:

int iPlayerID = 1337;
LOG(info) << "Player " << iPlayerID << "Connected";

[Thu Jan 29 18:32:11 2015] [info] Player 1337 Connected

解决方案

std::cout is not a function, it's an object of type std::ostream which overloads operator<<.

A quick sketch of how you could do it:

enum Level {
    debug, error, warning, info
};

struct Logger {
    std::ostream* stream;  // set this in a constructor to point
                           // either to a file or console stream
    Level debug_level;
public:
    Logger& operator<<(const std::string& msg)
    {
        *stream << msg; // also print the level etc.
        return *this;
    }

    friend Logger& log(Logger& logger, Level n);
    {
        logger.debug_level = n;
        return logger;
    }
};

Ant then use it like

Logger l;
log(l, debug) << "test";

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