Re: Pre-main construction order in modules

On Sun, 30 Mar 2025 10:38:57 -0400
James Kuyper <jameskuyper@alumni.caltech.edu> wibbled:

On 3/30/25 4:57 AM, Muttley@DastardlyHQ.org wrote:

I was curious about the order in which objects get constructed in modules
before main gets called. It seems with both Clang and gcc its the order in
which the modules were linked together to form the runnable binary so if
the link order was m1.o m2.o then anything in m1 would get constructed first.

>

Vice verca if you switch the order.
 
Is this codified in the standard or is it left up to compiler and linker
writers to decide how they order this?

>
Section 6.9.3.3 does in fact impose many constraints on the sequence in
which non-local objects with static storage duration get initialized.
However, all of the sequence requirements are only between objects
defined in the same translation unit. Also, it's implementation-defined
which of those initializations occur before the start of main().

Initialising global objects before main is an absolute must otherwise how
are you expected to use them safely? They're not in the code for decoration.