Syntax highlighting in emacs. Marking different data types with different colours

Question

In Emacs, is it possible to mark all variables of different data types with different colors? e.g. if I have the following variables in C/C++ my program

int i,j;
float g,h;
char a,b; 

Then throughout the source code i and j would be marked as red, g and h as green, a and b as blue.

I am not sure how useful this will be in future, but I feel it would help me while reading code, and be a good alternative to the Hungarian notation(not that I use this notation :D).

Answer 1

No. Emacs has no idea about the type of a specific expression; doing this would be tantamount to writing a significant part of a C compiler in ELisp.

However, there is a light at the end of the tunnel.

E.g., if you edit OCaml code using tuareg-mode, you can ask Emacs about the type of any expression because the ocaml compiler provides that information; thus you should be able to ask it to highlight variables by type. This is the path to follow.

Alas, gcc does not provide that information; however, its extensiongccxml does.

Also, other C compilers, e.g., clang, provide that information out of the box, and there is a new file semantic-clang.el which relies on those features (although for completion only, not for syntax highlighting).

So, nothing out of the box for you here, but if you are willing to use clang instead of gcc and contribute to the CEDET development, you might get what you want.