The blog post "It is not a compiler error (2017)" explores a subtle bug related to floating-point comparisons in C++. The author demonstrates how seemingly innocuous code, involving comparing a floating-point value against zero after decrementing it in a loop, can lead to unexpected infinite loops. This arises because floating-point numbers have limited precision, and repeated subtraction of a small value from a larger one might never exactly reach zero. The post emphasizes the importance of understanding floating-point limitations and suggests using alternative comparison methods, like checking if the value is within a small tolerance of zero (epsilon comparison), or restructuring the loop condition to avoid direct equality checks with floating-point numbers.
Bjarne Stroustrup's "21st Century C++" blog post advocates for modernizing C++ usage by focusing on safety and performance. He highlights features introduced since C++11, like ranges, concepts, modules, and coroutines, which enable simpler, safer, and more efficient code. Stroustrup emphasizes using these tools to combat complexity and vulnerabilities while retaining C++'s performance advantages. He encourages developers to embrace modern C++, utilizing static analysis and embracing a simpler, more expressive style guided by the "keep it simple" principle. By moving away from older, less safe practices and leveraging new features, developers can write robust and efficient code fit for the demands of modern software development.
Hacker News users discussed the challenges and benefits of modern C++. Several commenters pointed out the complexities introduced by new features, arguing that while powerful, they contribute to a steeper learning curve and can make code harder to maintain. The benefits of concepts, ranges, and modules were acknowledged, but some expressed skepticism about their widespread adoption and practical impact due to compiler limitations and legacy codebases. Others highlighted the ongoing tension between embracing modern C++ and maintaining compatibility with existing projects. The discussion also touched upon build systems and the difficulty of integrating new C++ features into existing workflows. Some users advocated for simpler, more focused languages like Zig and Jai, suggesting they offer a more manageable approach to systems programming. Overall, the sentiment reflected a cautious optimism towards modern C++, tempered by concerns about complexity and practicality.
Summary of Comments ( 74 )
https://news.ycombinator.com/item?id=43112187
HN users discuss integer overflow in C/C++, focusing on its undefined behavior and the security implications. Some highlight the dangers, especially in situations where the compiler optimizes away overflow checks based on the assumption that it can't happen. Others point out that
-fwrapvcan enforce predictable wrapping behavior, making code safer but potentially slower. The discussion also touches on how static analyzers can help catch these issues, and the inherent difficulties in ensuring complete safety in C/C++ due to the language's flexibility. A few commenters mention alternatives like Rust, which offer stricter memory safety and overflow handling. One commenter shares a personal anecdote about an integer underflow vulnerability they found in a C++ program, emphasizing the real-world impact of these seemingly theoretical problems.The Hacker News post "It is not a compiler error (2017)" linking to a blog post about subtle C++ template issues generated a moderate amount of discussion, with a number of commenters sharing their own related experiences and insights.
Several commenters agreed with the author's premise that template errors can be incredibly obtuse and difficult to decipher. One commenter highlighted the frustration of encountering such errors, especially when they manifest as seemingly unrelated issues far from the actual source of the problem. They recounted an experience where a template error caused a cascade of cryptic error messages throughout their codebase, making it a nightmare to debug. Another commenter echoed this sentiment, emphasizing the sheer volume and complexity of error messages that can arise from even minor template mishaps. They pointed out that these errors often require a deep understanding of template metaprogramming and the C++ type system to unravel.
Some commenters offered practical advice for mitigating the pain of template errors. One suggestion involved using concepts (C++20 and later) to provide more descriptive and targeted error messages when template parameters don't meet the required constraints. Another commenter recommended employing static analysis tools and compiler extensions to catch potential template issues early in the development process. They also suggested breaking down complex templates into smaller, more manageable components to simplify debugging.
A few commenters discussed the trade-offs between the power and flexibility of C++ templates and the complexity they introduce. While acknowledging the potential for difficult-to-debug errors, they argued that the benefits of generic programming and code reusability offered by templates outweigh the drawbacks. One commenter specifically mentioned how templates enable writing highly performant code by allowing the compiler to perform optimizations tailored to specific types.
One comment thread delved into the specific example presented in the blog post, analyzing the underlying causes of the error and discussing alternative approaches to achieve the desired functionality. This discussion highlighted the intricacies of template argument deduction and the importance of carefully considering the interactions between different parts of a template.
Finally, some commenters simply expressed their shared frustration with C++ template errors, offering commiseration and solidarity with the author and other developers who have wrestled with similar issues. They lamented the steep learning curve associated with mastering C++ templates and the occasional feeling of helplessness when faced with an avalanche of incomprehensible error messages.