log4cpp::PatternLayout – Available log4cpp log formats

log4cpp supports three layouts: Simple Layout, Basic Layout and PatternLayout. Simple and Basic Layout are the simplest ones and you need not configure them in any way. The display the log in a fixed format. log4cpp::PatternLayout has the additional advantage that it supports four different formats and provides a mechanism to create a format of your own.

PatternLayout has the following constructor

log4cpp::PatternLayout::PatternLayout()

which can be used to initialize a layout. There are four log formats

1. DEFAULT_CONVERSION_PATTERN = “%m%n”
2. SIMPLE_CONVERSION_PATTERN = “%p – %m%n”
3. BASIC_CONVERSION_PATTERN = “%R %p %c %x: %m%n”
4. TTCC_CONVERSION_PATTERN = “%r [%t] %p %c %x – %m%n”

By default, the DEFAULT_CONVERSION_PATTERN is used to display the logs. This is the simplest log format which simply displays the log message followed by a line separator (newline).
To make use of other formats, you can use

void log4cpp::PatternLayout::setConversionPattern(const std::string &conversionPattern)

substitute conversionPattern with any of the above patterns. For more information on what each of the symbols %d, %m mean, check PatternLayout definition.

The following program makes use of PatternLayoout

#include <stdio.h>
#include <stdlib.h>
#include <log4cpp/category.hh>
#include <log4cpp/OstreamAppender.hh>
#include <log4cpp/PatternLayout.hh>

using namespace std;

int main()
{
 /*Setting up Appender, <span id="IL_AD4">layout</span> and Category*/
 log4cpp::Appender *appender = new log4cpp::OstreamAppender("OstreamAppender",&cout);

 log4cpp::PatternLayout *layout = new log4cpp::PatternLayout();
 log4cpp::Category& category = log4cpp::Category::getInstance("Category");

 appender->setLayout(layout);
 category.setAppender(appender);
 category.setPriority(log4cpp::Priority::INFO);

 category.info("This is for tracing the flow");
 layout->setConversionPattern(log4cpp::PatternLayout::SIMPLE_CONVERSION_PATTERN);
 category.notice("This is to notify certain events");
 layout->setConversionPattern(log4cpp::PatternLayout::BASIC_CONVERSION_PATTERN);
 category.warn("This is to generate certain warnings");
 layout->setConversionPattern(log4cpp::PatternLayout::TTCC_CONVERSION_PATTERN);
 category.error("This is to generate errors");
}

The output of the program as seen on the standard output

This is for tracing the flow
NOTICE - This is to notify certain events
1263459000 WARN Category : This is to generate certain warnings
0 [-1608374496] ERROR Category  - This is to generate errors

See how we make use of all the above patterns in our program

Tags: Log Analysis, log4cpp, log4cpp examples, log4cpp PatternLayout, Pattern Layout