Error Logging in C++: The Power of clog

When it comes to error handling in C++, developers have two primary options: cerr and clog. While both are associated with stderr, they differ in a crucial way. clog stands out with its buffered output, making it a more efficient choice for non-critical error logging.

The Efficiency of Buffered Output

Buffered output is the key to clog’s efficiency. Instead of writing to disk every time an error occurs, clog saves the output in a variable and writes it all at once. This approach reduces the number of disk writes, making it faster than unbuffered output. However, there’s a catch: buffered output isn’t ideal for critical errors. In the event of a system crash, the output might still be in the buffer, and the error message could be lost forever.

Critical Errors Require Immediate Attention

For critical errors, it’s essential to prioritize reliability over efficiency. That’s why cerr is often used for critical error logging. Even though it’s slower, cerr ensures that error data is written to disk immediately, minimizing the risk of data loss in case of a system crash.

clog: The Preferred Choice for Non-Critical Logging

For non-critical event logging, efficiency takes center stage. clog’s buffered output makes it the perfect choice for logging non-critical errors. Its efficiency ensures that your application runs smoothly, while still providing valuable insights into non-critical errors.

Declaring clog

clog is defined in the <iostream> header file and is initialized during or before the first time an object of type ios_base::Init is constructed. Unlike cerr, clog is not tied to any other stream. The “c” in clog stands for “character,” making it a character log.

Using clog with the Insertion Operator

clog is used in conjunction with the insertion operator (<<) to display a stream of characters. The general syntax is straightforward: clog << variable/string/manipulator. You can combine variables, strings, and manipulators (like endl) to create a comprehensive log message.

A Practical Example

Here’s an example program that demonstrates how clog works:
“`
// Using clog for non-critical error logging

include

include

int main() {
std::ofstream file(“example.txt”);
if (!file) {
clog << “Error opening file: ” << strerror(errno) << std::endl;
}
return 0;
}
“`
In this example, clog is used to stream log data because the error is not critical to the application. When you run the program, the output will indicate an error opening the file, if such an error occurs.