10 C++ Logging Best Practices

Logging is an essential part of software development, and C++ is no exception. Logging helps developers debug their code, track errors, and monitor performance. But logging can also be a source of security vulnerabilities if not done properly.

In this article, we’ll discuss 10 best practices for logging in C++. We’ll cover topics such as logging levels, log rotation, and secure logging. By following these best practices, you can ensure that your C++ code is secure and your logs are useful.

1. Use a logging library

Logging libraries provide a consistent and easy-to-use interface for logging messages. This makes it easier to write code that is both readable and maintainable, as well as providing features such as log levels, message formatting, and more.

Using a logging library also helps ensure that your logs are consistent across different parts of the application. Without a logging library, each developer may have their own style of logging, making it difficult to read and interpret the logs. A logging library can help standardize this process, making it easier to debug issues in production.

2. Log to standard error stream or file

The standard error stream is a special output stream that can be used to log errors and other important messages. It’s also the default destination for all logging messages, so you don’t have to worry about configuring your application to use it. Additionally, since the standard error stream is always available, you can be sure that your logs will be written even if something goes wrong with your application.

Finally, by using the standard error stream or file, you can ensure that your logs are easily accessible and readable. This makes debugging much easier and helps you quickly identify any issues in your code.

3. Write log messages in UTF-8 encoding

UTF-8 is a universal character encoding that supports all languages and symbols. This means that when you write log messages in UTF-8, they will be readable by any system or application regardless of the language it uses.

This is especially important if your application needs to support multiple languages. By writing log messages in UTF-8, you can ensure that everyone who reads them will understand what they mean. Additionally, this helps prevent errors caused by incorrect character encodings.

4. Don’t use C++ iostreams for logging

C++ iostreams are slow and inefficient, which can lead to performance issues in your application. Additionally, they don’t provide the flexibility that a logging library does, such as being able to log to multiple destinations (e.g., files, databases, etc.).

Instead of using C++ iostreams for logging, use a dedicated logging library like spdlog or Boost Logging. These libraries offer more features than C++ iostreams, including better performance, thread safety, and support for multiple logging levels. They also make it easier to customize your logging output, so you can get exactly the information you need from your logs.

5. Format your log messages with placeholders

Placeholders allow you to easily insert dynamic values into your log messages, which makes them more informative and easier to read.

For example, instead of writing a message like this: “The user attempted to login with the wrong password”, you can use placeholders to write something like this: “The user [username] attempted to login with the wrong password”. This way, you can quickly identify who is attempting to login without having to search through the logs for their username.

Placeholders also make it easy to add additional information to your log messages, such as timestamps or other contextual data. This helps you better understand what happened when an error occurred, making it easier to debug and fix any issues that arise.

6. Avoid string concatenation when formatting log messages

String concatenation is a slow process, and when you’re dealing with logging, speed is of the essence. Logging should be as fast as possible so that it doesn’t interfere with your application’s performance. Additionally, string concatenation can lead to memory leaks if not done correctly.

Instead of using string concatenation, use C++’s stream-based formatting capabilities. This allows you to quickly format log messages without having to worry about memory management or performance issues.

7. Make sure that each message has a unique identifier

When debugging an issue, it’s often necessary to search through log files for specific messages. If each message has a unique identifier, it makes it much easier to find the exact message you’re looking for. This is especially important when dealing with large log files that contain thousands of lines of text.

Unique identifiers also make it easier to track down issues in production environments. By having a unique identifier associated with each message, it’s possible to quickly identify which messages are related to a particular problem and trace them back to their source.

8. Add context information to the log messages

When debugging an issue, it’s often difficult to determine the root cause without additional context. Adding contextual information such as the source file name, line number, and function name can help you quickly identify where the log message originated from. This makes it easier to trace back the code path and pinpoint the exact location of the problem.

Additionally, adding contextual information to your logs helps you better understand how a particular piece of code is behaving in different scenarios. For example, if you add the user ID or session ID to each log message, you can easily track the behavior of a specific user over time.

9. Consider adding severity levels to the log messages

Adding severity levels to log messages allows you to quickly identify the most important issues and prioritize them. For example, if a message is marked as “critical” or “error”, then it should be addressed immediately. On the other hand, if a message is marked as “warning” or “info”, then it can wait until later. This makes it easier for developers to focus on the most pressing issues first.

Additionally, adding severity levels to log messages helps with debugging. By being able to quickly identify which messages are more severe than others, developers can narrow down their search and find the root cause of an issue faster.

10. Configure the logger at runtime

When you configure the logger at runtime, it allows for more flexibility and control over how your logs are written. You can set different levels of logging for different parts of your code, as well as specify which log files should be used for each type of log message. This makes it easier to debug issues in production environments since you can quickly identify where a problem is occurring.

Additionally, configuring the logger at runtime also helps improve performance by reducing the amount of unnecessary logging that takes place. By setting specific thresholds for when certain types of messages should be logged, you can ensure that only relevant information is being recorded.