On Wed, 4 Apr 2012, Honza wrote:
2012/4/4 <[email protected]>:
Thank you for the help. Unfortunately I'm now confused even more. I
believe it's my fault, not yours.
You can always modify them (it's just data in memory), but modifying them
will only change your private view of the variables. The changes you make
will not propagate to libraries or newly started processes.
If "library" means a .so (or .dll, but Windows are not that much of a
Posix system), then it is in in-process space, so I would think the
change *does* propagate, i.e. the change is observable by a call to
getenv() from inside a library function. About started processes see
below.
Typically, libraries will read the environment variables at startup.
Any subsequent change to the environment will not have any effect.
Therefor it makes no sense to change them, and the FPC runtime does not
allow
it. If we did allow it, people would expect DOS/Windows like behaviour,
which
we simply cannot provide.
If you read the second part of the provided URL, you'll see that the POSIX
group recognises that the behaviour of setenv() is problematical.
The URL points - for restrictions - to the exec function
http://pubs.opengroup.org/onlinepubs/007904975/functions/exec.html
Where it says:
"For those forms not containing an envp pointer ( execl(), execv(),
execlp(),
and execvp()), the environment for the new process image shall be taken from
the external variable environ in the calling process."
The extrn char **environ (just environ from now on) points to the
environment variables of the executing process. Setenv may mutates
this environment. The various forms of exec do have either explicit
envp, so one can create any required environment vars set, or pass the
current environ, effectively enabling the inheritance of the (posibly
mutated) environment as an option.
The other forms, w/o envp, are defined to do exactly that, i.e. they
will use the current environ as their environment vars pointer,
Not the current.
The EXTERNAL variable environ, i.e. the one that the kernel passed on,
which cannot be modified. You can only modify your local copy.
Michael.
--
_______________________________________________
Lazarus mailing list
[email protected]
http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
