Massive fprintf speed difference without “-std=c99”

Question

I had been struggling for weeks with a poor-performing translator I had written. On the following simple bechmark

#include

int main()
{
    i         


        

Answer 1

After some consideration of your assembler, it looks like the slow version is using the *printf() implementation of MinGW, based undoubtedly in the GCC one, while the fast version is using the Microsoft implementation from msvcrt.dll.

Now, the MS one is notably for lacking a lot of features, that the GCC one does implement. Some of these are GNU extensions but some others are for C99 conformance. And since you are using -std=c99 you are requesting the conformance.

But why so slow? Well, one factor is simplicity, the MS version is far simpler so it is expected that it will run faster, even in the trivial cases. Other factor is that you are running under Windows, so it is expected that the MS version be more efficient that one copied from the Unix world.

Does it explain a factor of x10? Probably not...

Another thing you can try:

• Replace fprintf() with sprintf(), printing into a memory buffer without touching the file at all. Then you can try doing fwrite() without printfing. That way you can guess if the loss is in the formatting of the data or in the writing to the FILE.