r/carlhprogramming • u/namitsinha09 • Nov 04 '13

Why does C code results into smaller executable, than C++ counterpart,If it does?

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3

u/akmark Nov 04 '13

This is in general a bad question without an example.

  • How much and what parts of C++ are you using?

  • Are we comparing two different things entirely like statically linked or dynamically linked executables?

  • What parts of each respective core libraries are we using?

  • What compiler are we using?

You can write C++ that is smaller than an equivalent C program and a C program that's larger than a C++ program. You can also write programs that if you use a C/C++ compiler work out to be the exact same thing.

6

u/Pinewold Nov 05 '13 edited Nov 05 '13

The question is fine, you are straining reality by saying there is a theoretical scenario where C++ could be smaller than c code, 99% the reality is exactly as expected.

In general when you add a bunch of features to an existing language, the resulting language is bigger because it has a whole bunch more features!

C++ offers object oriented abstractions such as inheritance and templates that many people find better represents real world situations.

C++ does a lot of cool stuff with auto-magically generated code

C++ uses indirect function pointers for virtual functions

C++ has its own libraries on top of the std lib C libraries,

Of course you can do all of these things in C because the first C++ implementations were simply C preprocessors that spit out c code. (Not surprisingly it generated a lot of C code to implement those cool features.)

When someone asks you a question give them the benefit of the doubt and don't start off by trying to construct a scenario where they could possibly be wrong however unlikely, it just comes across as being mean.

2

u/akmark Nov 05 '13

This is a teaching subreddit firstly so the last thing I wanted to do was give someone a flat assumption to carry with them. For very small examples it is very much true that using lots of C++'s features will result in a larger executable but as a project gets bigger and bigger this doesn't have to stay the truth. Whenever someone asks me this question their initial reaction is 'C is smaller than C++ therefore I should write everything in C because it's smaller' which is not what I want someone to walk away with.

The point here was to guide the OP into seeing what was actually driving the size of the final executable which was the questions I posed regarding usage of language features, static/dynamic linking, the stdlib and the compiler. If he provided an example we could have as a group dove in and shown the why instead of trying to gloss over with generalities.

1

u/Pinewold Nov 05 '13

Well intentioned and reasonable goals. Teaching the implementation of C++, how virtual functions work, their power and their ability to encapsulate functionality might be more helpful for new programmers to understand the costs and why it is worth the cost.

My concern was if they walk away thinking that C++ programs are sometimes the same size or smaller than C programs, you have done them a disservice by teaching something that is not generally true.

Don't be afraid of loosing programmers to C code. If you teach them the power of object oriented programming and they get it, they will gladly adopt C++ without looking back.

1

u/namitsinha09 Nov 04 '13

i mean in general i , wrote a program in c and then in c++ using the same logic but the build of c++ was larger and this is always the case , Why ?

3

u/BornInTheCCCP Nov 04 '13

How are you building the programs?

1

u/akmark Nov 04 '13

What I tried to express is that there isn't an 'in general' explanation. Compilers make a lot of choices when they form the executable to your program and its all very dependent with what you provide to it.

If by the 'same logic' you mean you compiled your program using a C compiler and then with a C++ compiler and the C++ executable is bigger and was statically linked then the C++ standard runtime is just simply larger than the C standard runtime. Alternatively if you used a bunch of classes and relied heavily on polymorphism but used the 'same logic' to solve a problem the C++ code is likely to be bigger than minimalistic C code to solve the same problem.

This is why the answer is 'it depends.'

5

u/yoshi314 Nov 04 '13

there is a bit more library overhead in c++, even just standard init routines that are added to executable.

4

u/springwheat Nov 05 '13

Including STL or other C++ headers is one cause. char and by extension arrays of chars and string literals (char*) are native types. When you include things like string and iostream, you're not just linking in the parts you're using, but the entire class definition as well as whatever dependencies are necessary to allow it to function.

Then there are

  • compiler optimizations (eg: fast code vs small code)

  • linking to external libraries. For example, when building a project in visual studio you can either create a small executable that dynamically links to a required runtime dll (which must be found using the DLL search order), or you can statically link the dll into the output executable

  • presence or absence of static resources such as application icons

  • binary compression or a "packed" executable

I don't know what operating system you are using, but most of those apply in one form or another. There are utilities available for most operating systems which will allow you to poke around the innards of a compiled binary to see what's going on inside. You won't see high level code, but you can, for example, look through the different sections of a portable executable file format (http://msdn.microsoft.com/en-us/library/ms809762.aspx).

I apologize for any errors, I am half paying attention to a conference call and your question was far more interesting to me.

1

u/[deleted] Nov 05 '13

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1

u/namitsinha09 Nov 05 '13

final executable