Remove comments in a C file

Question

I am trying to remove comments from a file which may be in any part of a line and span multiple lines.

 struct my_struct{
  field1;
  field2; /** comment 1
  */ field3;
  /* comment 2 */
 } struct_name;

I need to get

struct my_struct{
  field1;
  field2; 
  field3;
 } struct_name;

I tried using

grep -o '[^/*]*[^*/]'

to remove any text between matching /* and */, but it is eliminating the comment symbols but not the text in between. What is the correct way? If there is another way using 'sed', it would be nice to know that too.

I doubt you can do it in grep, as it matches line-by-line. awk is definitely possible, and sed may be too. — Sparhawk, Oct 20 '16 at 21:05
Also: How can I delete all characters falling under /* … */ including /* & */? — ilkkachu, Oct 20 '16 at 21:20

score 3 · Answer 1 · answered Oct 20 '16 at 21:11

3

You can do it with a C compiler : gcc :

gcc -fpreprocessed -dD -E -P file.c

check man gcc

answered Oct 20 '16 at 21:11

Gilles Quénot

33,867

Some discussion on the ups and downs of using cpp for that, here: http://unix.stackexchange.com/a/297375/170373 – ilkkachu Oct 20 '16 at 21:21
Yes, check this one especially: http://unix.stackexchange.com/questions/297346/how-can-i-delete-all-characters-falling-under-including/297375#comment522655_297375 – Gilles Quénot Oct 20 '16 at 21:24
This too: http://unix.stackexchange.com/questions/297346/how-can-i-delete-all-characters-falling-under-including/297375#comment523813_297375 – ilkkachu Oct 20 '16 at 21:25

score 2 · Accepted Answer · answered Oct 20 '16 at 21:27

If you just want to remove anything between /* and */, and ignore all the quirks of the C language, like C99-style //-comments, quoted strings and backslash-escapes of newlines, then a simple Perl-regex should do:

perl -0777 -pe 's,/\*.*?\*/,,gs' inputfile

Remove comments in a C file

2 Answers2

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