Just FYI: The reason they're using gcc-4.2 comparisons is that Apple
employees are banned from using GPLv3 software. E.g. if you report a
bug to them that requires checking out a newer version of GCC they'll
just shrug and say "sorry, but we can't try it out".
Oh, and the diagnostics are much better, and not just because they're
in color. Consider e.g. this program:
hello.c: In function ‘main’:
hello.c:5: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘char *’
While clang gives you:
hello.c:5:20: warning: conversion specifies type 'int' but the argument has type 'char *' [-Wformat]
printf("hello %d", "world");
~^ ~~~~~~~
Clang tells you not only the line that had the error but also the
column, then it higlights the %d format argument, and shows you which
argument you gave doesn't fit with it.
Pretty much all of its diagnostics messages are like that. While you
sometimes have to stare at code for 5-10 seconds to see what GCC is
complaining about clang will tell you exactly what the problem is.
"The diagnostics were a little prettier than gcc-4.5's, but not a huge improvement." <- I think this example fits with this description: gcc clearly stated it was the second argument... it is nice that it pointed out to me what the second argument is, but I can count. A little prettier, but not a drastic improvement.
I think what most of us are really looking when someone claims that they have better diagnostics is to do something for cases that are currently incomprehensible. As an example: if you run into an error in a recursive template, sometimes you are scratching your head at an error that seems to have no direct semantic meaning. When I was really doing a lot of C++, I started to accumulate a mental map of "when gcc claims that X has occurred, what that really means is that I should try explicitly adding a template or typename keyword to a nearby expression".
I've seen people new to C struggle with what I think are relatively simple GCC diagnostic messages. I think they're somewhat simple now since I'm used to them and know C.
But pointing out exactly the bit of code that's wrong, and often what you should do about it is - I think - a huge improvement.
Oh, and the diagnostics are much better, and not just because they're in color. Consider e.g. this program:
GCC will give you: While clang gives you: Clang tells you not only the line that had the error but also the column, then it higlights the %d format argument, and shows you which argument you gave doesn't fit with it.Pretty much all of its diagnostics messages are like that. While you sometimes have to stare at code for 5-10 seconds to see what GCC is complaining about clang will tell you exactly what the problem is.