Question

I am transitioning from C to C++. In C++, is there any use for the malloc function, or can I just use the new keyword? For example:

class Node {
    /* ... */
};

/* ... */

Node *node = malloc(sizeof(Node));
// vs
Node *node = new Node;

Which one should I use?

Answer 1

Use new. You shouldn’t need to use malloc in a C++ program, unless it is interacting with some C code or you have some reason to manage memory in a special way.

Your example of node = malloc(sizeof(Node)) is a bad idea, because the constructor of Node (if any exists) would not be called, and a subsequent delete node; would have undefined results.

If you need a buffer of bytes, rather than an object, you’ll generally want to do something like this:

char *buffer = new char[1024];
// or preferably:
std::unique_ptr<char[]> buffer = std::make_unique<char[]>(1024);
// or alternatively:
std::vector<char> buffer(1024);

Note that for the latter examples (using std::vector or std::unique_ptr), there is no need to delete the object; its memory will automatically be freed when it goes out of scope. You should strive to avoid both new and malloc in C++ programs, instead using objects that automatically manage their own memory.

Here are your options and their benefits:

Method	Dynamically Sized	Automatically Managed	Resizable
std::array<char, N>	No	Yes	No
new char[N]	Yes	No	No
std::unique_ptr<char[]>	Yes	Yes	No
std::vector<char>	Yes	Yes	Yes