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How do you set autotools default C++ compilation flags

I am quite new with using autotools and I am still learning.

So, as stated in the title of my topic I would like to know how to set compilation flags.

I know there already has been a topic on this but it didn't solve my problem :

I used :

...
AC_SUBST([AM_CXXFLAGS], [-Wall -Werror])
...

but unfortunately, when using ./configure I get:

...
./configure: line 3436: -Wall: command not found
...

and as a result it produces Makefiles but with no targets

Thank you in advance for any help

Solution

  • The answer provided by Idav1s works for me as well because

    AC_SUBST([FOO], [BAR QUUX])

    expands to the following shell code:

    FOO=BAR QUUX

    which runs QUUX with the FOO environment variable set to BAR. In your case, this means AM_CXXFLAGS is set to -Wall, and -Werror is executed. Why you're seeing -Wall executed instead is unknown to me... For me, the error happened on line 2802:

    configure: line 2802: error: -Werror not found

    So I opened the configure script, and what I found was the AM_CXXFLAGS=-Wall -Werror on line 2802. Changing it to ['-Wall -Werror'] in configure.ac fixed things for me.

    The Autotools build system is quite portable, and it makes cross-compilation easier than some build systems (e.g. Cmake requires a toolchain file with special variables set). I wouldn't suggest switching build systems just yet as a solution to such a simple problem.