Problem with UNIX/Linux Shared Libraries and Global variables ...

[viraj.kadakia]

I observe a behavior with shared libraries (.so) and global variables
that I cannot understand ...
I'd appreciate if someone can explain the behavior ..

Scenario 1:
aTest is an executable on Solaris/Linux built from main.o (main.cpp)
bTest dynamically loads a shared libraires mylib1.so and mylib2.so
both built from mylibsrc.o (mylibsrc.cpp)
cmylibsrc.cpp contains a global variable 'int MyGlobal' that is non
static and not extern (simply int MyGlobal)
dI have extern C Set and Get functions in mylibsrc.cpp to access
MyGlobal
eUnder these circumstatnces, when I run Test, MyGlobal seems to have
two instances in memory, one for each .so
Their runtime values (modified by dlsym(handle, Set)) and
addresses are different as expected.

Scenario 2:
aEverything is same as Scenario 1 except ..
bmain.cpp (Test) also has a global non-static, non-extern variable
'int MyGlobal'
cNow when I run Test, all 3 MyGlobal(s) (in Test, mylib1.so and
mylib2.so) are the same memory address and same value.

Why is the behavior under these to scenarios different ?
I expect that MyGlobal in main.cpp should have its own instance ...

p.s. I use -fPIC / -KPIC and -Bsymbolic while generating the .so(s)

Thanks in advance ...

[Jack Klein]

On Fri, 20 Jun 2008 18:01:10 -0700 (PDT), vi***********@g mail.com
wrote in comp.lang.c:

I observe a behavior with shared libraries (.so) and global variables
that I cannot understand ...
I'd appreciate if someone can explain the behavior ..

I am sure someone can, in an appropriate group like
news:comp.unix. programmer or news:comp.os.li nux.development .apps.

You are off-topic here, the C language does not define the details of
specific tool sets and features like shared libraries.

Scenario 1:
aTest is an executable on Solaris/Linux built from main.o (main.cpp)
bTest dynamically loads a shared libraires mylib1.so and mylib2.so
both built from mylibsrc.o (mylibsrc.cpp)

And even more off-topic here. The C++ language defines ways to link
code to compatible C compilers, the C language does not define linkage
to any other language at all.

But this is more of a platform issue than a C++ one.

--
Jack Klein
Home: http://JK-Technology.Com
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