Difference between cerr and clog in C++

The cerr and clog are both stream objects in C++ that are connected to the standard error device, and their actions differ slightly. The ostream class contains the objects cerr and clog, which are used to output error messages and other diagnostic data to the standard error stream. In this article, you will learn about the difference between cerr and clog in C++. But before discussing these differences, you must know about the cerr and clog in C++.

What is the cerr (Standard Error Stream)?

The cerr stands for "character error" which represents the "standard error stream". It is an ostream class instance that is automatically connected to the console, the standard error device. Cerr's primary feature is its unbuffered nature. It is significant in the context of error messages because the output sent to cerr is flushed instantly. It ensures that error messages are shown immediately, even during an unexpected program termination.

Example:

Let us take an example to illustrate the use of the cerr function in C++.

#include <iostream>
using namespace std;
int main() {
cerr << "This is an error message." << endl;
return 0;
}

Output:

What is the clog (Standard Logging Stream)?

The "clog" stands for "character logging", which represents the "Standard error stream". It is similar to cerr, clog is linked to the standard error device and is an instance of the ostream class. But unlike cerr, clog is buffered, meaning that it is kept in a buffer instead of flushing the output right away. The buffer is flushed under some circumstances, such as a normal program exit.

Example:

Let us take an example to illustrate the use of the clog function in C++.

#include <iostream>
using namespace std;
int main() {
clog << "This is a log message." << endl;
return 0;
}

Output:

Main Difference between Cerr and Clog:

There are several main differences between the Cerr and Clog in C++. Some main differences between the Cerr and Clog are as follows:

Use the Cerr function when you want to guarantee that critical error messages are displayed right away, even if the program crashes.
Use the Clog function for general logging applications, where a small display delay is acceptable and buffered output may be more effective, use clog.

S.No	cerr	clog
1.	This standard error stream is not buffered.	This standard error stream is buffered.
2.	It's employed to show the error.	It's employed in logging.
3.	It's employed to show the message right away.	It is unable to instantly display the message.
4.	The message cannot be stored for later display.	It can store messages in the buffer to display them later.
5.	The cerr is an acronym for "character error", where "err" is an abbreviation for "error" and "c" stands for "character".	As "log" means "logging" and "c" stands for "character", the term "clog" stands for "character logging".
6.	It is less efficient than clog due to its unbuffered output.	It is more efficient than Cerr due to its buffered output.
7.	It is recommended for critical errors (errors that can result in system crashes).	It is not recommended for critical errors (errors that can result in system crashes).

Conclusion:

Both cerr and clog can be helpful in practice; which one you use will depend on your program's requirements and the importance of the data you are sending to the standard error stream.

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