Detect ICC vs GCC at compile time

Question

How to detect at compile time if I'm using gcc or icc?

(I was quite puzzled to find out that icc defines __GNUC__ -- and even __GNUC_MINOR__ and __GNUC_PATCHLEVEL__ ! why?)

Answer 1

We use

#ifdef __INTEL_COMPILER

to split icc off, assuming gcc as a default.

Answer 2

I believe you could check for __INTEL_COMPILER according to this.

Answer 3

The reason ICC defines __GNUC__ etc. is because of code like yours that is inspecting compiler-specific macros and expects to see them...

Answer 4

Traditionally, compilers have defined a symbol of their own as well as their version as preprocessor symbols so that the code could be adapted (generally to work around bugs or specificities).

CLang has introduced a mechanism I had not seen so far, under the form of the __has_feature query. It does not replace the "work around bugs" practices (which is why CLang still exposes specific symbols) but allows a more natural style for querying the compiler capacities. I don't know if other compilers plan on defining such a facility.

Answer 5

You can make the processor output the defined macros in the preprocessor output and look for a macro that suits you. You can generated the preprocessor output like this:

icc  -dM -E -o foo.P foo.c

Then look at foo.P (since it is a text file). In my case, I found icc defined an __ICC macro with the version of the compiler. It didn't define any __INTEL_COMPILER though.