Back in 2020, at 19 years old, I had just entered university, filled with excitement to finally learn advanced C++. I was eager to understand those weird, cryptic concepts that only the C++ masters seemed to know. By that point, I had already been learning C++ for over five years and felt stuck at what I considered 'level 4 out of 5' in my C++ journey. I was genuinely excited to tackle the truly difficult concepts.

I spoke to a student a year ahead of me about the C++ course, mentioning my existing knowledge and readiness for any challenge. His reply was blunt: "No, you have no idea what you're up against. You are not prepared for what you'll be doing in university. It's extremely hard. Forget anything you think you know."

While that might sound intimidating, it was exactly what I wanted. I was determined to finally reach 'level 5' of C++ mastery. I entered the class with high expectations, only to discover that the curriculum covered what I'd call 'level 3' C++. In other words, I was already well beyond the scope of the course.

But here’s the interesting part: most people believe this is 'advanced' C++, when in fact, it's only scratching the surface. In this article, we'll explore the different levels of C++ proficiency to help you identify where you stand. More importantly, we'll discuss whether it's worth striving for 'level 5,' delving into advanced C++ topics with unusual examples, explaining the language's evolution, and offering guidance on what to learn and where to find the resources.

The Levels of C++ Proficiency

Level 1: The Absolute Beginner

This is the starting point of your C++ journey. You're not yet familiar with what a compiler is, and you might even tell people you've 'installed C++' on your computer. At this stage, errors are your greatest foe, and listing C++ on your resume would be a major overstatement. Your skills are limited to printing 'Hello, World!' to the console and perhaps creating a very simple calculator. The good news is, with a bit of practice, you'll quickly advance to the next level.

Level 2: The Basics

Technically, you're still a beginner. Errors remain a significant challenge, and it's still too early to add C++ to your skillset on a CV. However, you now understand fundamentals like functions and can create simple programs that have practical use.

This level extends beyond just functions. You grasp the concepts of classes, memory allocation, and perhaps some basic elements of the C++ Standard Library. By this point, you've likely decided whether to pursue a programming career. If so, you can look forward to a rewarding path, creating projects that contribute to society.

Level 3: 'Advanced' in Quotes

Level 3 is particularly interesting because many developers who reach this stage believe they have mastered advanced C++. I was once one of them.

At this level, you're comfortable with common Standard Library features like unique_ptr and various algorithms. You understand polymorphism and are familiar with more nuanced C++ rules such as downcasting, upcasting, the diamond problem in inheritance, and the Rule of Three/Five/Zero. Most introductory C++ interview questions will target this level of knowledge.

The primary reason many developers stop here is that the vast majority of courses and tutorials don't venture into more complex topics, leading to the assumption that this is the extent of C++. In reality, you've barely scratched the surface. We are just getting started.

Level 4: Real Advanced C++

Once you realize how much more there is to learn, you begin the journey to level 4: true advanced C++. This is where things get fascinating. C++ is a mature language that has evolved significantly over decades. Many new features had to be integrated without breaking backward compatibility. The result is a language that is powerful but sometimes less elegant than it could be.

The Power of Templates

Templates are a perfect example. Generic programming became a critical paradigm, and C was lacking in this area. C++ introduced templates to fill this gap. Initially, they were intended as a simple mechanism to create the same implementation for different data types. However, developers soon discovered that templates were far more powerful than originally conceived.

For instance, let's say you want a templated function to work exclusively with float or double types. Here’s how you can achieve that:

First, create a templated struct and then add a specialization for it: ```cpp template struct isfloator_double {};

template <> struct isfloator_double { using type = void; };

template <> struct isfloator_double { using type = void; }; `` We've created a membertypethat only exists if we provide afloator adouble`.

Finally, we use this in our function's implementation: cpp template <typename T, typename = typename is_float_or_double<T>::type> void my_function(T value) { // ... function implementation } If you attempt to call this function with an int, the compilation will fail. This happens because the compiler tries to access the type member, which doesn't exist for integers. This technique is known as SFINAE (Substitution Failure Is Not An Error), and it's just the beginning. We also have advanced concepts like CRTP (Curiously Recurring Template Pattern), variadic templates, and the fact that templates are Turing complete, meaning you can theoretically write any computer program using only templates.

Interestingly, many of these capabilities were discovered by accident, and the C++ standard committee later embraced them, even adding helper utilities for SFINAE and other template metaprogramming techniques. The challenge, however, is that as you delve into more complex template usage, the code can become incredibly intricate. I once encountered a bizarre issue where I had to explicitly use the template keyword to inform the compiler that a member was a template; otherwise, the code wouldn't compile. I can guarantee that the vast majority of C++ developers will never encounter such an obscure problem.

Let's contrast this with a more modern language like Zig. In Zig, you can write standard code that executes at compile-time. Essentially, Zig doesn't need templates because you can use regular code for metaprogramming. If you need a loop, you can write a simple for loop instead of resorting to complex template recursion. Instead of SFINAE, you can use a straightforward if statement. C++ is gradually moving in this direction with features like if constexpr, but the progress is slow.

Here’s a classic example of level 4 C++ knowledge. Suppose you want to remove all elements smaller than 10 from a std::vector. A common approach is to use std::remove_if with a lambda function. cpp std::vector<int> v = {5, 12, 3, 15, 8}; std::remove_if(v.begin(), v.end(), [](int i){ return i < 10; }); If you think this code correctly removes the elements, you'd be mistaken. You also need to call the erase member function. The remove_if algorithm doesn't actually remove any elements; it just shuffles them to the end of the container and returns an iterator to the new logical end. This is a well-known quirk of the language.

The correct way is the erase-remove idiom: cpp v.erase(std::remove_if(v.begin(), v.end(), [](int i){ return i < 10; }), v.end()); In the example above, I used a lambda—essentially an anonymous function—to specify the removal condition. But what if I told you we could rewrite this without a lambda? It's possible to use a struct with operator overloading to create an object that behaves like that lambda. I've implemented this for several operators, inspired by a feature in the Boost libraries that achieves even more complex behaviors.

Level 5: The C++ Guru (And Why You Might Not Need It)

At this point, you might expect me to claim I'm a 'level 5 C++ God,' but I'm not. In this section, I'll explain why I believe aiming for level 5 might not be the best use of your time and what you should focus on instead. A 'level 5 C++ guru' is someone who knows nearly all the esoteric features of the language, the standard library, and its many strange behaviors. Let me give you a sense of what that entails.

For example, you might know how to read an entire file in a single line of code: ```cpp

include

include

include

std::ifstream t("file.txt"); std::string str((std::istreambufiterator(t)), std::istreambufiterator()); Or you might know that you can add an execution policy flag to certain standard algorithms to run them in parallel: cpp

include

include

include

// ... std::vector myvector; // ... std::sort(std::execution::par, myvector.begin(), my_vector.end()); ``` But if you already knew these, you're likely at level 4. There are far more obscure features. For instance, C++ has facilities for formatting time, and you can even overload operators to create your own user-defined string literals.

The Dangers of Over-Complexity

While we could explore more of these C++ quirks, I want to discuss something more critical: why I don't recommend focusing exclusively on these highly advanced topics and what a better approach might be. You have to understand that a primary goal of C++ was to enable generic programming while maintaining high performance. It succeeded in this, but as a pioneer in this space, the resulting syntax and usage can be unwieldy.

Let's take an example. You have standard references (&) and then you have r-value references (&&). You can think of an r-value reference as a reference to a temporary object. When a function returns a std::vector, it's returned as a temporary. A move constructor can then use an r-value reference to 'steal' the internal data from this temporary, avoiding a costly memory allocation. This concept isn't too difficult on its own, but the complexity builds.

Now consider a 'forwarding reference' (also known as a 'universal reference'). It uses the same && syntax but appears in a templated context. A forwarding reference can bind to both l-values (like a normal reference) and r-values, depending on the argument passed. To preserve the value category, you must use std::forward when passing it on. If you find this confusing, that's precisely the point. And what I've described so far is still knowledge that many advanced C++ developers possess.

The Vector Implementation Challenge

Let's imagine you want to implement your own version of std::vector. It's a template class, so it must work correctly with any type you pass to it, whether it's a simple int or a complex class that manages its own resources. You have to handle memory allocation, object construction, and destruction with extreme care. Here's the major problem: unless you are a level 5 C++ guru, it is nearly impossible to guarantee that your implementation is perfectly correct for all possible types and scenarios.

C++ is statically typed, which helps catch errors at compile time, and you can write tests to verify behavior. But for a generic container like this, how can you be certain you've handled move semantics, copy semantics, and exception safety correctly for every conceivable edge case? I once attempted this, implemented unit tests, and was confident in my code. Yet, every time I revisited the project, I found new bugs. After sharing it, others found even more problems.

Some might say this is a 'skill issue' and that I just need to 'learn C++ better.' But let's think critically. I have been programming in C++ for over a decade. I can build a multiplayer game from scratch with multithreading, yet I struggle to correctly implement the most fundamental data structure. I am not exaggerating when I say I am more confident in the correctness of a lock-free, multi-threaded server I've written than in a simple vector implementation.

The reality is that writing such generic code correctly is incredibly difficult. The reason the standard library implementation of std::vector is over 4,000 lines of code is because that level of complexity is necessary to ensure its correctness and robustness.

Remember the operator overloading struct I mentioned for replacing a lambda? The implementation is highly complex, and most developers would struggle to understand it. All that complexity was just to create a slightly different syntax for a simple comparison. The more you program, the more you realize that writing your own highly generic code is often overrated. It's usually better to use the powerful features already provided by the C++ standard library and keep your own code simple. Using if constexpr for compile-time decisions is a great example of a modern feature that helps without adding excessive complexity.

The Takeaway: Simplicity Over Complexity

To be clear, you should absolutely learn about advanced C++ features if it's your primary language. However, your application code should not look like a standard library implementation—riddled with convoluted templates, obscure generic programming tricks, and hard-to-decipher logic. If I can't guarantee the correctness of a simple vector, how can anyone expect to write a large, bug-free application in that style? The key is to write simple, readable, and easily debuggable code.

This philosophy is why I don't rush to adopt every new feature from C++20 or newer standards. While they are undoubtedly powerful, I find that the existing feature set is more than sufficient for my needs. The code for my game project, for instance, primarily uses plain, simple, and readable C++, although I admit that some additional compile-time features are always welcome.

So, what does this mean for you? It's crucial to learn how C++ works. Once you reach an advanced level, however, it's more beneficial to spend your time building large, practical projects, such as a game engine or a complex application. This is where true mastery is built—not just in knowing the language's obscure corners, but in using it effectively to create something tangible.