Thread: c preprocessor output issue with comments after #include

Why can't I add add a comment after a c directive ?
For eg.
I added the following line in a .c file

#include <a.h> /* test comment*/

I tried the c preprocessor (gcc -E) to output the preprocessed output.

I am using 3.4.6 version of gcc
The preprocessor output with the following options -C -dI -dD -undef didn't give me the comment after #include
It only outputs if I add the comment in the next line as follows.
#include <a.h>
/* test comment*/

It works as expected when I tried it out with an older version of gcc - 2.95.4
Does this mean something is broken in the newer version of gcc or a new option is required to output the comment after the directive.

well since #include's arent really C, the #include line may be terminated by a newline, that is, everything after the #include is considered the statement. therefore no comments

i dont know though and i dont think it really matters, just put the comment above the line where it should be

if this is the most difficult part of your program then id be very happy

This really matters to me since I have a code generation tool where it uses the preprocessed o/p. Currently this is one way to pass on some info to the tool to do some validation/control the generated code. For eg. I could say #include <a.h> /* ignore */
The 'ignore' key word is checked in the code generation tool to control the generated code.

The following are the first four (of eight) phases of translation specified in the C Standard:

Trigraph Replacement - The preprocessor replaces trigraph sequences with the characters they represent.
Line Splicing - Physical source lines that are continued with escaped newline sequences are spliced to form logical lines.
Tokenization - The preprocessor breaks the result into preprocessing tokens and whitespace. It replaces comments with whitespace.
Macro Expansion and Directive Handling - Preprocessing directive lines, including file inclusion and conditional compilation, are executed. The preprocessor simultaneously expands macros and, in the 1999 version of the C standard, handles _Pragma operators.

C preprocessor - Wikipedia, the free encyclopedia

cant you just change how this code generation tool works so to get around this problem? ie, have it look elsewhere for the 'ignore' keyword?

id also like to know what this means

It works as expected when I tried it out with an older version of gcc - 2.95.4

what does "work as expected" mean? what do you intend to happen when you place a comment after a #include? because the #include is just a way to say "copy stuff in here later", so the only thing that makes sense (from the preprocessor's side) would be to expand out the #include and put the comment after it. but you seem to want something else...

edit: you could just compile with older versions of gcc

When I used gcc - 2.95.4 with '-E -C' option, even if I have comment in the same line of the c directive it gives me the comment in the output, #include <a.h> /* ignore */ gives me /* ignore */ in the o/p.
When I upgrade the gcc to 3.4.6, the comment disappears.
I need to go to the latest gcc version for some other reason. I have no option.
I was wondering why would the latest gcc behaves differently here with the same options.
Anyway, if I don't have any other solution, I will have to change the code generator.
The requirement for me is to control the output as follows.
If I say #include <a.h> /* ignore */ , that would mean, preprocess a.h, but I don't want "#include <a.h>" in the output.