In C++, am I paying for what I am not eating?

Question

Let\'s consider the following hello world examples in C and C++:

main.c

#include 

int main()
{
    printf(\"Hello world\\n\");
    r         


        

Answer 1

There are a few misconceptions to start with. First, the C++ program does not result in 22 instructions, it's more like 22,000 of them (I pulled that number from my hat, but it's approximately in the ballpark). Also, the C code doesn't result in 9 instructions, either. Those are only the ones you see.

What the C code does is, after doing a lot of stuff that you don't see, it calls a function from the CRT (which is usually but not necessarily present as shared lib), then does not check for the return value or handle errors, and bails out. Depending on compiler and optimization settings it doesn't even really call printf but puts, or something even more primitive.
You could have written more or less the same program (except for some invisible init functions) in C++ as well, if only you called that same function the same way. Or, if you want to be super-correct, that same function prefixed with std::.

The corresponding C++ code is in reality not at all the same thing. While the whole of it is well-known for being a fat ugly pig that adds an immense overhead for small programs (in a "real" program you don't really notice that much), a somewhat fairer interpretation is that it does an awful lot of stuff that you don't see and which just works. Including but not limited to magical formatting of pretty much any haphazard stuff, including different number formats and locales and whatnot, and buffering, and proper error-handling. Error handling? Well yes, guess what, outputting a string can actually fail, and unlike the C program, the C++ program would not ignore this silently. Considering what std::ostream does under the hood, and without anyone getting aware of, it's actually pretty lightweight. Not like I'm using it because I hate the stream syntax with a passion. But still, it's pretty awesome if you consider what it does.

But sure, C++ overall is not as efficient as C can be. It cannot be as efficient since it is not the same thing and it isn't doing the same thing. If nothing else, C++ generates exceptions (and code to generate, handle, or fail on them) and it gives some guarantees that C doesn't give. So, sure, a C++ program kinda necessarily needs to be a little bit bigger. In the big picture, however, this does not matter in any way. On the contrary, for real programs, I've not rarely found C++ performing better because for one reason or another, it seems to lend for more favorable optimizations. Don't ask me why in particular, I wouldn't know.

If, instead of fire-and-forget-hope-for-the-best you care to write C code which is correct (i.e. you actually check for errors, and the program behaves correctly in presence of errors) then the difference is marginal, if existent.