How can I see the C/C++ #include graph easily?

Doxygen, with the aid of Graphviz, can do that. You first need to edit a configuration file. This won't be easy the first time you do it, but no much editing is needed afterwards.

First, cinclude2dot.pl is a perl script which analyses C/C++ code and produces a #include dependency graph as a dot file for input into graphviz.

http://www.flourish.org/cinclude2dot/

If you don't want to go the way of that sort of manual tool, then the hands-down by far winner is in my opinion a tool known as "IncludeManager" from ProFactor.

http://www.profactor.co.uk/includemanager.php

There's a free trial, and it is awesome. It's a plug-in for Visual Studio that's totally integrated so double clicking on something over here takes you to the place where it is included over there.

Tooltip mouseovers give you all the info you would want, and it lets you drill down / up, remove whole subtrees you don't care about, view representations other than graphs, cycle through a list of matches for this and that, it's wonderful.

If you're quick about it, you can refactor the #include structure of a large projects before the trial runs out. Even so, it doesn't cost much, about $35 per license.

For what it does, it is just about perfect. Not only #include graphs but also cross project dependencies of shared files, impact on build times, detailed properties in grids, perfect.

Not quite what you want perhaps, but the Visual Studio compiler (cl.exe) has an option /showIncludes which will show you a tree of the includes when you compile a file.

If you want this information for a single file then you can right-click on the file in the Solution Explorer, select "Properties", and in the "Command Line" section just add /showIncludes to the "Additional Options". (Note I'm using VC++ 2005, so it may be different for newer versions).

The output that you get is a little... convoluted, but it shows you what gets included and in what order.

Incidentally, the same feature in GCC and the Intel C++ compiler (my versions at least) is -H.