Comparing C and C++ usage and performance with a real world project

Post by khitchdee » Sun, Sep 03, 2017, 7:31 PM UTC

nly wrote: post #45

khitchdee wrote: post #15

If you ignore the protection mechanisms and the class heirarchy built into C++, then a C++ class is like a C struct that can contain function pointers. For many programs this is all that's needed, and the amount of overhead involved in using such an approach to creating objects is obviously lower. So there's no question C will always be faster. It's only when you need protection and class heirarchies that C++ benefit…

> a C++ class is like a C struct that can contain function pointers. No, it's not. Calling an ordinary class member function in C++ has exactly the same overhead as calling a function in C. Even virtual functions in C++ are not the same as putting function pointers in a C struct (they live in a separate data structure called the vtable). > the protection mechanisms and the class heirarchy All C++ protection mechanism…

Post by astrobe_ » Sun, Sep 03, 2017, 7:41 PM UTC

jackmott wrote: post #81

zvrba wrote: post #23

Earlier quoted context omitted.

> As for the "memory leaks" --- I haven't looked at the source, but something whose runtime is very short-lived, like pkg-config, may be very well justified in allocating and never freeing, letting the process exit itself be the "ultimate free". But sometimes the code grows and what was once a stand-alone executable is about to become a component in a larger executable. With C++ you get a correct component out of the…

bit of a tautology there. correct if correct.

Post by humanrebar » Sun, Sep 03, 2017, 8:05 PM UTC

khitchdee wrote: post #69

humanrebar wrote: post #56

Earlier quoted context omitted.

It's true that generative programming can make up for shortcomings of C. But you're pretty much writing in two languages at that point, C and whatever spec generated the rest of the C code. It's not an apples-to-apples comparison to C++.

Well, some parts of the generative programming could be built into a tool and you probably wouldn't have to rewrite a generative program each time. So it's not really writing in 2 languages but using code generation to assist the programming process to reduce potential for error as a more flexible alternative to creating fixed constructs in a purpose built language.

Post by mcguire » Sun, Sep 03, 2017, 8:18 PM UTC

khitchdee wrote: post #82

nly wrote: post #45

Earlier quoted context omitted.

> a C++ class is like a C struct that can contain function pointers. No, it's not. Calling an ordinary class member function in C++ has exactly the same overhead as calling a function in C. Even virtual functions in C++ are not the same as putting function pointers in a C struct (they live in a separate data structure called the vtable). > the protection mechanisms and the class heirarchy All C++ protection mechanism…

Doesn't a vtable imply an extra level of indirection? You have to find where the vtable is in the object, then the function within the vtable, right? Is that not slower?

Post by bch » Sun, Sep 03, 2017, 8:33 PM UTC

astrobe_ wrote: post #83

bch wrote: post #68

Earlier quoted context omitted.

> That's THEIR problem then. It is their problem, clearly. > Why should the original author care for that? That's the question. Don't you think it's easy to think of reasons, though? What if the person porting the code to a library was a later version of the original author?

Will you also call them lazy because they didn't care about being thread safe or UTF8-ready?