本文介绍了使用log4cplus有六个步骤，并提供了一些例子引导你了解log4cplus的基本使用。
### 基本使用 ###
使用log4cplus有六个基本步骤：
1. 实例化一个appender对象
2. 实例化一个layout对象
3. 将layout对象绑定(attach)到appender对象
4. 实例化一个logger对象,调用静态函数：log4cplus::Logger::getInstance("logger_name")
5. 将appender对象绑定(attach)到logger对象，如省略此步骤，标准输出（屏幕）appender对象会绑定到logger
6. 设置logger的优先级，如省略此步骤，各种有限级的消息都将被记录
下面通过一些例子来了解log4cplus的基本使用。
〖例1〗
/**//* 严格实现步骤1-6，appender输出到屏幕, 其中的布局格式和LogLevel后面会详细解释。*/
#include <log4cplus/logger.h>
#include <log4cplus/consoleappender.h>
#include <log4cplus/layout.h>
using namespace log4cplus;
using namespace log4cplus::helpers;
int main()
{
/**//* step 1: Instantiate an appender object */
SharedObjectPtr _append (new ConsoleAppender());
_append->setName("append for test");
/**//* step 2: Instantiate a layout object */
std::string pattern = "%d{%m/%d/%y %H:%M:%S} - %m [%l]%n";
std::auto_ptr _layout(new PatternLayout(pattern));
/**//* step 3: Attach the layout object to the appender */
_append->setLayout( _layout );
/**//* step 4: Instantiate a logger object */
Logger _logger = Logger::getInstance("test");
/**//* step 5: Attach the appender object to the logger */
_logger.addAppender(_append);
/**//* step 6: Set a priority for the logger */
_logger.setLogLevel(ALL_LOG_LEVEL);
/**//* log activity */
LOG4CPLUS_DEBUG(_logger, "This is the FIRST log message")
sleep(1);
LOG4CPLUS_WARN(_logger, "This is the SECOND log message")
return 0;
}
输出结果：
10/14/04 09:06:24 - This is the FIRST log message... [main.cpp:31]
10/14/04 09:06:25 - This is the SECOND log message... [main.cpp:33]
〖例2〗
/**//* 简洁使用模式，appender输出到屏幕。*/
#include <log4cplus/logger.h>
#include <log4cplus/consoleappender.h>
using namespace log4cplus;
using namespace log4cplus::helpers;
int main()
{
/**//* step 1: Instantiate an appender object */
SharedAppenderPtr _append(new ConsoleAppender());
_append->setName("append test");
/**//* step 4: Instantiate a logger object */
Logger _logger = Logger::getInstance("test");
/**//* step 5: Attach the appender object to the logger */
_logger.addAppender(_append);
/**//* log activity */
LOG4CPLUS_DEBUG(_logger, "This is the FIRST log message")
sleep(1);
LOG4CPLUS_WARN(_logger, "This is the SECOND log message")
return 0;
}
输出结果：
DEBUG - This is the FIRST log message...
WARN - This is the SECOND log message...
〖例3〗
/**//* iostream模式，appender输出到屏幕。*/
#include <log4cplus/logger.h>
#include <log4cplus/consoleappender.h>
#include <iomanip>
/**//* 其实这个东东还是放到log4cplus头文件中比较合适些，个人意见：） */
using namespace log4cplus;
int main()
{
/**//* step 1: Instantiate an appender object */
SharedAppenderPtr _append(new ConsoleAppender());
_append->setName("append test");
/**//* step 4: Instantiate a logger object */
Logger _logger = Logger::getInstance("test");
/**//* step 5: Attach the appender object to the logger */
_logger.addAppender(_append);
/**//* log activity */
LOG4CPLUS_TRACE(_logger, "This is" << " just a t" << "est." << std::endl)
LOG4CPLUS_DEBUG(_logger, "This is a bool: " << true)
LOG4CPLUS_INFO(_logger, "This is a char: " << 'x')
LOG4CPLUS_WARN(_logger, "This is a int: " << 1000)
LOG4CPLUS_ERROR(_logger, "This is a long(hex): " << std::hex << 100000000)
LOG4CPLUS_FATAL(_logger, "This is a double: " << std::setprecision(15) << 1.2345234234)
return 0;
}
输出结果：
DEBUG - This is a bool: 1
INFO - This is a char: x
WARN - This is a int: 1000
ERROR - This is a long(hex): 5f5e100
FATAL - This is a double: 1.2345234234
〖例4〗
/**//* 调试模式，通过loglog来控制输出调试、警告或错误信息，appender输出到屏幕。*/
#include <iostream>
#include <log4cplus/helpers/loglog.h>
using namespace log4cplus::helpers;
void printMsgs(void)
{
std::cout << "Entering printMsgs()" << std::endl;
LogLog::getLogLog()->debug("This is a Debug statement");
LogLog::getLogLog()->warn("This is a Warning");
LogLog::getLogLog()->error("This is a Error");
std::cout << "Exiting printMsgs()" << std::endl << std::endl;
}
int main()
{
/**//* LogLog类实现了debug, warn, error 函数用于输出调试、警告或错误信息， 同时提供了两个方法来进一步控制所输出的信息，其中：
setInternalDebugging方法用来控制是否屏蔽输出信息中的调试信息，当输入参数为false则屏蔽，缺省设置为false。
setQuietMode方法用来控制是否屏蔽所有输出信息，当输入参数为true则屏蔽， 缺省设置为false。
LogLog::getLogLog()->setInternalDebugging(false); */
printMsgs();
std::cout << "Turning on debug" << std::endl; LogLog::getLogLog()->setInternalDebugging(true); printMsgs();
std::cout << "Turning on quiet mode" << std::endl;
LogLog::getLogLog()->setQuietMode(true);
printMsgs();
return 0;
}
输出结果：
Entering printMsgs()...
log4cplus:WARN This is a Warning...
log4cplus:ERROR This is a Error...
Exiting printMsgs()...
Turning on debug...
Entering printMsgs()...
log4cplus: This is a Debug statement...
log4cplus:WARN This is a Warning...
log4cplus:ERROR This is a Error...
Exiting printMsgs()...
Turning on quiet mode...
Entering printMsgs()...
Exiting printMsgs()...
需要指出的是，输出信息中总是包含"log4cplus:"前缀，有时候会感觉不爽，这是因为LogLog在实现时候死定了要这么写：
LogLog::LogLog() : mutex(LOG4CPLUS_MUTEX_CREATE),
debugEnabled(false),
quietMode(false),
PREFIX( LOG4CPLUS_TEXT("log4cplus: ") ),
WARN_PREFIX( LOG4CPLUS_TEXT"log4cplus:WARN ") ),
ERR_PREFIX( LOG4CPLUS_TEXT"log4cplus:ERROR ") ){}
你可以把这些前缀换成自己看着爽的提示符号，然后重新编译，hihi。除非万不得已或者实在郁闷的不行，否则还是不要这样干。
〖例5〗
/* 文件模式，appender输出到文件。*/
#include <log4cplus/logger.h>
#include <log4cplus/fileappender.h>
using namespace log4cplus;
int main()
{
/* step 1: Instantiate an appender object */
SharedAppenderPtr _append(new FileAppender("Test.log"));
_append->setName("file log test");
/* step 4: Instantiate a logger object */
Logger _logger = Logger::getInstance("test.subtestof_filelog");
/* step 5: Attach the appender object to the logger */
_logger.addAppender(_append);
/* log activity */
int i;
for( i = 0; i < 5; ++i )
{
LOG4CPLUS_DEBUG(_logger, "Entering loop #" << i << "End line #")
}
return 0;
}
输出结果（Test.log文件）：
DEBUG - Entering loop #0End line #
DEBUG - Entering loop #1End line #
DEBUG - Entering loop #2End line #
DEBUG - Entering loop #3End line #
DEBUG - Entering loop #4End line #