Re: Can you help me summarize all the bad things with global variables?

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 11 Sep 2010 11:12:53 -0700 (PDT)

Message-ID:

<9ecfccf9-e93a-4c71-a39a-452a7ad8e394@m16g2000vbs.googlegroups.com>

On Sep 10, 11:13 pm, Paavo Helde <myfirstn...@osa.pri.ee> wrote:

Seungbeom Kim <musip...@bawi.org> wrote
innews:i6e5oi$all$1@usenet.stanford.edu:

On 2010-09-09 14:11, Paavo Helde wrote:

3) Needs locking or other synchronization in multi-threaded program
if not constant.

4) Can become a bottleneck in multi-threaded programs.

5) Behavior can be unpredictable in multi-threaded programs (like one
thread changing the global locale while the other is outputting
data).

I'm not convinced that these are problems of global variables per se.
You have the same cautions with local variables, too, don't you?

Local statics, yes. Local automatic variables, no.

Why not? As you say:

But you are right, the multi-threading problems appear
wherever the variable is visible to multiple threads.

When using pthread (and Windows threads as well, I presume),
it's quite usual to pass the address of a local variable as the
thread argument when creating a thread. (Passing a pointer to a
dynamically allocated object is probably more frequent, but both
cases occur relatively frequently.)

--
James Kanze