Category: Clang

Comparing MSVC vs Clang

Comparing MSVC vs Clang

Listing of some C codeI originally created Asteroids for Windows using Visual Studio 2017 Community Edition. Since then I’ve started the Clang version on Ubuntu and there haven’t been too many differences but there are just a few so in this post I’ll list what I’ve found so far.

Include Paths

On Windows, I was able to get away with #include <SDL.h> but on Linux, I’ve had to include the path so it’s #include <SDL2/SDL.h>. This was probably because I included the full path in the MSVC configuration.

Link Failures

The asteroids.c code in chapter 29 uses sin and cos for the first time and the linker was unhappy with that. So in tasks.json, I’ve explicitly had to add it into args, along with SDL2 and SDL2_image,

            "args": [

That “-lm” does that for maths.

Safe functions

Microsoft has its own set of safe functions many with an _s and extra length parameter.

On Linux, there don’t seem to be so many.

So sprintf_s on Windows becomes snprintf.

fopen_s just becomes standard fopen


As well as time.h in the includes, I needed to add linux/time.h as well.

I’m considering switching to C11

I’m considering switching to C11

Programming image
Image by Gerd Altmann from Pixabay

All C code I write in the books is currently to the C99 standard. All the compilers involved (Visual C++ on Windows and Clang on Ubuntu) support C99 but C11 support seems restricted to GCC and Clang.

Microsoft has traditionally supported C++ but their C support seems a bit grudging; realistically they don’t prioritise it which I can understand.

Given though that I’m not going to republish my first e-book for a while (I’d like to add a WebAssembly chapter or two first), I’m going to investigate whether it’s worth switching to C11 for the 2nd book. From what I’ve read all it needs is a flag to tll it to compile to C11 standards. This is for Clang.


But the other question is what will I gain by doing this and I can’t actually see there’s that much benefit.. I don’t need Unicode, I don’t think alignment will really make much difference. You can read about the C11 changes on WikiChip.

So I’ve made the decision. I’ll stick with C99 for now. But for an alternative view, I recommend Danny Kalev’s 2012 article on C11.


That Clang C compilation

That Clang C compilation

I spent about five hours trying to get the timing code to compile before I got it compiling and working. Now I’m used to the concept of include guards in C. Those are the #ifndef that you see like this:

#ifndef _timeh
  #include <linux/time.h>
  #define _timeh 1

But in the hr_time.c file these include guards are on steroids. Not only did I need to include <time.h>, I also had to include <linux/time.h> but with a couple of extra #defines in there. It doesn’t seem right and wasn’t needed with the Windows version.  I’d welcome any comments on this.

#ifndef _timeh
  #include <linux/time.h>
  #define __timespec_defined 1 
  #define __itimerspec_defined 1
  #include <time.h>
  #define _timeh 1

The sdldemo program with timing whown in the window caption.Without these, I’d get compile errors like __timespec redefined errors.

I’ve uploaded the source files and Visual Studio Code JSON files for this in the file in the new repository for the Learn C on Linux Ebook

So feel free to try it. The only difference between this and the version shown in an earlier post is the time (in the window caption) to draw all 100,000 rectangles,  You’ll need to install SDL2 if you want to compile and run the program.