Unwanted warning message with g++

Question

I am trying to write a c++ extension for Ruby. In addition to the main file, I have a file extconf.rb:

require "mkmf"
$libs += " -lstdc++ "
create_makefile("file_name")

and, after doing ruby extconf.rb, when I try to compile it with g++ by typing make, I get the warning:

cc1plus: warning: command line option "-Wdeclaration-after-statement" is valid for C/ObjC but not for C++

I read that it is not harmful, but is there a way to avoid this warning? There is a person with the same problem here, but the solution cannot be found.

Answer 1

Edit the resulting Makefile created after running create_makefile and remove the -Wdeclaration-after-statement from there.

Answer 2

Try this in your extconf.rb:

$warnflags.gsub!('-Wdeclaration-after-statement', '') if $warnflags

the if $warnflags is needed because mkmf changed in Ruby 1.9.3; without it you'll get undefined method `gsub!' for nil:NilClass if you try to build on Ruby 1.9.2. You shouldn’t get the c++ warning in 1.9.2 though: the default warnings Ruby uses changed in 1.9.3 and these have been added.

Update:

This is probably better:

CONFIG['warnflags'].gsub!('-Wdeclaration-after-statement', '')

$warnflags gets populated from this, but this doesn't need the if $warnflags for < 1.9.3.