Comment by ryao

I doubt that because C++ encourages heavy use of dynamic memory allocations and data structures with external nodes. C encourages intrusive data structures, which eliminates many of the dynamic memory allocations done in C++. You can do intrusive data structures in C++ too, but it clashes with object oriented idea of encapsulation, since an intrusive data structure touches fields of the objects inside it. I have never heard of someone modifying a class definition just to add objects of that class to a linked list for example, yet that is what is needed if you want to use intrusive data structures.

While I do not doubt some C++ code uses intrusive data structures, I doubt very much of it does. Meanwhile, C code using <sys/queue.h> uses intrusive lists as if they were second nature. C code using <sys/tree.h> from libbsd uses intrusive trees as if they were second nature. There is also the intrusive AVL trees from libuutil on systems that use ZFS and there are plenty of other options for such trees, as they are the default way of doing things in C. In any case, you see these intrusive data structures used all over C code and every time one is used, it is a performance win over the idiomatic C++ way of doing things, since it skips an allocation that C++ would otherwise do.

The use of intrusive data structures also can speed up operations on data structures in ways that are simply not possible with idiomatic C++. If you place the node and key in the same cache line, you can get two memory fetches for the price of one when sorting and searching. You might even see decent performance even if they are not in the same cache line, since the hardware prefetcher can predict the second memory access when the key and node are in the same object, while the extra memory access to access a key in a C++ STL data structure is unpredictable because it goes to an entirely different place in memory.

You could say if you have the C++ STL allocate the objects, you can avoid this, but you can only do that for 1 data structure. If you want the object to be in multiple data structures (which is extremely common in C code that I have seen), you are back to inefficient search/traversal. Your object lifetime also becomes tied to that data structure, so you must be certain in advance that you will never want to use it outside of that data structure or else you must do at a minimum, another memory allocation and some copies, that are completely unnecessary in C.

Exception handling in C++ also can silently kill performance if you have many exceptions thrown and the code handles it without saying a thing. By not having exception handling, C code avoids this pitfall.