Why is it a bad idea to use 'new'? [duplicate]

Answer 1

Is it really a bad idea to use 'new' in instantiating a class in C++?

It’s often bad because it’s not necessary, and code gets much easier when you’re not using it spuriously. In cases where you can get away without using it, do so. I’ve written whole libraries without once using new.

I get that using raw pointers is ill-advised, but why have a 'new' keyword at all when it's such bad practice? Or is it?

It’s not universally bad, just unnecessary most of the time. But there are also times when it’s appropriate and that’s why there is such a keyword. That said, C++ could have gotten away without the keyword, since new conflates two concepts: 1. it allocates memory, and 2. it initialises the memory to an object.

You can decouple these processes by using other means of memory allocation, followed by a constructor invocation (“placement new”). This is actually done all over the place, such as the standard library, via allocators.

On the other hand, it’s rarely (read: never) meaningful for client code to manage uninitialised memory so it makes sense not to decouple these two processes. Hence the existence of new.