Reset the C/C++ preprocessor #line the physical file/line

Question

I have a code generator that's going to take some user-written code and embed chunks of it in a larger generated file. I want the underlying compiler to provide good diagnostics when there are defects in the user's code, but I also don't want defects in the generated code to be misattributed to the source when they shouldn't be.

I intend to emit #line lineNum "sourceFile" directives at the beginning of each chunk of user-written code. However, I can't find any documentation of the #line directive that mentions a technique for 'resetting' __LINE__ and __FILE__ back to the actual line in the generated file once I leave the user-provided code. The ideal solution would be analogous to the C# preprocessor's #line default directive.

Do I just need to keep track of how many lines I've written and manually reset that myself? Or is there a better way, some sort of reset directive or sentinel value I can pass to #line to erase the association with the user's code?

It looks like this may have been posed before, though there's no solid answer there. To distinguish this from that, I'll additionally ask whether the lack of answer there has changed with C++11.

Answer 1

A technique I've used before is to have my code generator output a # by itself on a line when it wants to reset the line directives, and then use a simple awk script to postprocess the file and change those to correct line directives:

#!/bin/awk -f
/^#$/ { printf "#line %d \"%s\"\n", NR+1, FILENAME; next; }
{ print; }

Answer 2

Yes, you need to keep track of the number of lines you've output, and you need to know the name of the file you're outputting into. Remember that the line number you specify is the line number of the next line. So if you've written 12 lines so far, you need to output #line 14 "filename", since the #line directive will go on line 13, and so the next line is 14.

There's no difference between the #line preprocessor directive in C and C++.