# log4cpp
## The first HelloWorld process of log4cpp
1. The relationship between Category,Appender and Layout is as follow：
> There are more than one Category in the system,and all of them are inherited from the same root,and each Category is responsible for recording its own log.Each Category can add mroe than one Appender.Each Appender specifies a destination for log,for example,a file,a character stream,or a windows log.when the Category records a log,the log is written to all the Appender attached to this Category.Each Appender includes a Layout,and this Layout define a format of the log on the Appender.
2. Now revist the previous HelloWorld program,and we can see that the process is as follows:
> 1. Create an Appender,and specify a Layout that is contains.
> 2. Get the root of Category from system,and add the Appender to this Category.
> 3. Setting the priority of the Category.
> 4. Record log.
> 5. close the Category.
## The Layout of log4cpp
###1. PatternLayout
1. Three subclass of Layout:
>
> * BasicLayout
> * PatternLayout
> * SimpleLayout
2. PatternLayout
>
> * %c category
> * %d date
> * %m message
> * %p priority
> * %n newline
> * %r ms after the layout created
> * %R seconds from 1970
> * %u the number of clock cycles to date from the beginning of the process
> * %x NDC
3. An ideal format
>
"%d: %p %c %x: %m%n"