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Learn C++ Through Projects @CppWithProjects

Learn to write idiomatic, performing, well-tested code that can be shipped to production 🚀 learncppthroughprojects.com Joined September 2020
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CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

The `explicit` keyword prevents unwanted type conversions. Class ctors that only take 1 param are special: They could be used to perform type conversions. If the ctor is marked as `explicit`, the conversion can only happen... well, explicitly. #learntocode #cpp #cplusplus

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

Pro tip #1: Use std::make_unique and std::make_shared to avoid explicit calls to `new`, so the object lifetime is fully tied to the lifetime of the smart pointer. Pro tip #2: Be mindful that shared_ptr has the additional cost of maintaining a reference count of its clones.

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

std::shared_ptr is the opposite. You can copy a shared_ptr as many times as you want: Each pointer points to the same object. When a shared_ptr goes out of scope, the pointed-to object is only destroyed if no other shared_ptr is pointing to it (shared_ptr keeps the count).

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

How smart is a C++ smart pointer? If you init a raw pointer with `new`: int* ptr = new int; then you must call `delete ptr` when you don't need it anymore. This is error prone! ❗️Smart pointers handle the lifetime of the pointed-to object for us. #cpp #cplusplus #learntocode

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

📖 A general guiding principle: If the code that generates the error is close to the expected error handler and in a tight loop → Return error codes. If the code that generates the error is far from the code that should handle it → throw an exception.

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

Broadly speaking, an exception that never throws has an insignificant runtime performance cost. A common alternative (returning error codes) has the fixed cost of checking for errors at every call. The best performance trade-off can only be informed by your own measurements.

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

How do exceptions work in C++? An exception is like a videogame checkpoint: We tell the program that if something goes wrong, we want to be taken back to the checkpoint. The path back to the checkpoint is not always easy though... #cpp #cplusplus #learntocode 🧵

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

With cmake_paths, conan downloads dependencies and lists their paths in a conan_paths.cmake file. If you include the file, CMake looks for dependencies in the conan folders. Without the file, CMake reverts to the default search paths, as usual.

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

If you want to use conan as a C++ package manager but don't want your CMake build system to depend on it, you can use the "cmake_paths" generator. #cpp #cplusplus #cmake #conan

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

@alcampk Do a full codebase refactoring every 6 months, or every 3 months if you live in an area with very hard water

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

@shafikyaghmour It would probably escape tests with that if logic — the fun begins if f() had opposite logic!

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

@Viladoman @basit_ayantunde @VisualStudio @visualc Nice!

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

We can still prevent the copy. Since C++14, we can initialize lambda captures with anything — including with a move assignment: auto printValue = [captured = std::move(value)] (...) { ... };

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

When creating lambdas, we often capture variables by reference to avoid unnecessary copies, but we need to be careful with the *lifetime* of the captured variable. 🚨 In the snippet below, `value` has gone out of scope by the time the lambda is called. #cpp #cplusplus

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

@DrAuraHxC Thank you for your support, it is really appreciated! We will be sending out a newsletter update in the first week of November, with a sneak peak as well 👀

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

@PeterSommerlad A type in this case!

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

rvalue references can be confusing! 👀 In the code below, is the the `Container&& cont` parameter copied or moved into the `local` variable? (assuming `Container` has both copy and move ctors) #cpp #cplusplus

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

We can call `std::move(cont)` and make sure that the move ctor is called instead. Because `print_value` takes an rvalue reference, it is understood that it can modify the `cont` object — even take ownership of it.

CppWithProjects Profile Picture

Learn C++ Through Projects @CppWithProjects

6 years ago

`cont` is copied into `local`, not moved. As a function arg, `cont` **accepts** rvalue references — that's why we pass a temporary to it in main. But in the context of the print_value function, `cont` is an lvalue, and so it initializes `local` through the Container copy ctor.

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