编写“可流动”的类。 [英] Writing classes which are "streamable"
问题描述
嗨！
我为我的项目写了一个日志类，我想支持
流语法，我想写的在我的代码中这样：
日志日志（MYPREFIX）;
log<< 这是一条消息，正在发送到syslog，value ="
<< 5;
我创建了一个朋友功能：
Log&运营商LT;< （Log& log，std :: string& str）;
现在我可以写：
log<< 只支持字符串;
但是这不起作用（当然）：
log<< 这将创建两条日志消息 << "为什么这不是
连接？" ;;
我想知道是否有人知道一些可以帮助我的文件
使我的日志类与流兼容。
问候，
Mikael
Hi!
I have written a logging class for my project and I want to support the
stream syntax, that is I would like to write like this in my code:
Log log("MYPREFIX");
log << "This is a message, which is being sent to syslog, value ="
<< 5;
I have created a friend function:
Log& operator<< (Log& log, std::string& str);
So now I can write:
log << "Only strings are supported";
However this doesn''t work (of course):
log << "This will create two log messages" << " why isn''t this
concatenated?";
I wonder if someone knows about some documentation which could aid me
in making my log class stream-compatible.
Regards,
Mikael
推荐答案
Mikael写道：
Mikael wrote:
嗨！
我为我的项目写了一个日志类，我想支持
stream语法，我想在我的代码中这样写：
日志日志（MYPREFIX）;
log<< 这是一条消息，正在发送到syslog，value ="
<< 5;
我创建了一个朋友功能：
Log&运营商LT;< （Log& log，std :: string& str）;
你确定你的功能需要修改str吗？如果没有，为什么它不是
const引用？
现在我可以写：
log<< 只支持字符串;
然而，这当然不起作用：
log<< 这将创建两条日志消息 << "为什么这不会连接？" ;;
你的意思是什么都不行，为什么当然？
我想知道是否有人知道某些文件这可以帮助我
使我的日志类流兼容。
Hi!
I have written a logging class for my project and I want to support the
stream syntax, that is I would like to write like this in my code:
Log log("MYPREFIX");
log << "This is a message, which is being sent to syslog, value ="
<< 5;
I have created a friend function:
Log& operator<< (Log& log, std::string& str);
Are you sure that your function needs to modify str? If not, why isn''t it a
const reference?
So now I can write:
log << "Only strings are supported";
However this doesn''t work (of course):
log << "This will create two log messages" << " why isn''t this
concatenated?";
What do you mean by "doesn''t work", and why "of course"?
I wonder if someone knows about some documentation which could aid me
in making my log class stream-compatible.
你可以从std :: ostream派生它，它将自动为你提供所有
为标准输出流定义的流操作符。
You could derive it from std::ostream, which will automatically give you all
the stream operators defined for the standard output streams.
Mikael写道：
Mikael wrote:
嗨！
我已经为我的项目编写了一个日志类，我想支持
流语法，我想在我的代码中这样编写：
日志日志（MYPREFIX）;
log<< 这是一条消息，正在发送到syslog，value ="
<< 5;
我创建了一个朋友功能：
Log&运营商LT;< （Log& log，std :: string& str）;
所以现在我可以写：
log<< 只支持字符串;
但是这不起作用（当然）：
发布更多代码，
Log&运营商LT;< （Log& log，std :: string& str）;
返回???
log<< 这将创建两条日志消息 << "为什么这不是连接的？" ;;
我想知道是否有人知道一些文件可以帮助我
使我的日志类流兼容。 />
问候，
Mikael
Hi!
I have written a logging class for my project and I want to support the
stream syntax, that is I would like to write like this in my code:
Log log("MYPREFIX");
log << "This is a message, which is being sent to syslog, value ="
<< 5;
I have created a friend function:
Log& operator<< (Log& log, std::string& str);
So now I can write:
log << "Only strings are supported";
However this doesn''t work (of course):
Post more code, what does
Log& operator<< (Log& log, std::string& str);
return ???
log << "This will create two log messages" << " why isn''t this
concatenated?";
I wonder if someone knows about some documentation which could aid me
in making my log class stream-compatible.
Regards,
Mikael
运营商< ;<定义如下（我已经添加了const
指出）：
Log&运营商LT;< （Log& log，std :: string const& str）
{
log.logMessage（str.c_str（））;
return记录;
}
对不起，如果我的问题太不明确，我会在下次尝试更详细
。
当我写下
以下代码时，上面的函数生成两条日志消息：
log<< ; 消息1 << " message 2"
因为运算符<<（）直接调用log.logMessage（）。
如果我派生自std :: ostream，我如何将格式化的
字符串放入我的日志中？如果你能说明它应该如何运作
那么？
如果这些都是愚蠢的问题，我很抱歉，我对溪流很陌生（我是/>
只使用了它们。
亲切的问候，
Mikael
The operator<< is defined as follows (I have added the const as you
pointed out):
Log& operator<< (Log& log, std::string const& str)
{
log.logMessage(str.c_str());
return log;
}
Sorry if my question was too unspecific, I will try to be more verbose
the next time.
The above function generates two log messages when I write the
following code:
log << "message 1" << "message 2";
because operator<<() calls log.logMessage() directly.
If I derive from std::ostream, how do I actually get the formatted
string into my log? If you could please clarify how it should work
then?
I am sorry if these are stupid questions, I am pretty new to streams (I
have only used them sofar).
With kind regards,
Mikael
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