I thoroughly endorse all the advice about RAII and smart pointers, but I’d also like to add a slightly higher-level tip: the easiest memory to manage is the memory you never allocated. Unlike languages like C# and Java, where pretty much everything is a reference, in C++ you should put objects on the stack whenever … Read more
A simple (and perhaps overused) example of RAII is a File class. Without RAII, the code might look something like this: File file(“/path/to/file”); // Do stuff with file file.close(); In other words, we must make sure that we close the file once we’ve finished with it. This has two drawbacks – firstly, wherever we use … Read more
The C++ Standard says that an STL element must be “copy-constructible” and “assignable.” In other words, an element must be able to be assigned or copied and the two elements are logically independent. std::auto_ptr does not fulfill this requirement. Take for example this code: class X { }; std::vector<std::auto_ptr<X> > vecX; vecX.push_back(new X); std::auto_ptr<X> pX … Read more
NO This is what RAII is for, let the destructor do its job. There is no harm in closing it manually, but it’s not the C++ way, it’s programming in C with classes. If you want to close the file before the end of a function you can always use a nested scope. In the … Read more
Throwing an exception out of a destructor is dangerous. If another exception is already propagating the application will terminate. #include <iostream> class Bad { public: // Added the noexcept(false) so the code keeps its original meaning. // Post C++11 destructors are by default `noexcept(true)` and // this will (by default) call terminate if an exception … Read more
No, C++ does not support ‘finally’ blocks. The reason is that C++ instead supports RAII: “Resource Acquisition Is Initialization” — a poor name† for a really useful concept. The idea is that an object’s destructor is responsible for freeing resources. When the object has automatic storage duration, the object’s destructor will be called when the … Read more
It’s a really terrible name for an incredibly powerful concept, and perhaps one of the number 1 things that C++ developers miss when they switch to other languages. There has been a bit of a movement to try to rename this concept as Scope-Bound Resource Management, though it doesn’t seem to have caught on just … Read more