global const variable not getting assigned properly

global const variable not getting assigned properly

[Chad Scholes]

I have the following global const defined at the top of a .cpp file:

const wchar_t * FILESPEC	= L"filespec";
const unsigned int LEN_PATH = 5  + wcslen(FILESPEC) ;


Then in a class method I reference LEN_PATH:

printf("The length is %d\n", LEN_PATH);

LEN_PATH is 0 (zero).  If I don't use the wide character version (change wchar_t to char and wcslen to strlen) then it works, I get LEN_PATH set to 13.  Also, if I just assign LEN_PATH = 5 or LEN_PATH = 5 + 8, then it also works.

Any idea why it is 0 when using wcslen?  And any idea why I'm not even getting an error to notify me of the problem?

Thanks!

Re: global const variable not getting assigned properly

[John Love-Jensen]

Hi Chad,

> Any idea why it is 0 when using wcslen?  And any idea why I'm not even getting
> an error to notify me of the problem?

Works on my platform with my version of GCC with the BSD Standard C Library
(ISO/IEC 9899:1999 compliant).

I'm guessing its either your Standard C Library or your version of GCC or
your platform.

What version of Standard C Library are you using?

Who is the provider of your Standard C Library (e.g., GLibC)?

What version of GCC are you using?

What platform are you using?

Also, your code snippet and explanation of the behavior is nice, but could
you provide a short complete code example that demonstrates the problem.
Maybe its something simple like you used the incorrect header files (e.g.,
<wchar.h> instead of <cwchar>).

And could you provide the GCC command line that you used to compile your
short complete code example.

Thanks,
--Eljay

Re: global const variable not getting assigned properly

[John Love-Jensen]

Hi Chad,

> Do you know why they are not getting initialized?

I presume because the .SO's global initializer is not being called.

> If I call dlopen instead will that help solve this problem?

Maybe.

> Is there something I can set to get those initialized before I use them?

Yes.

Instead of writing:
const int uno = 1;
const int dos = 2;
const int tres = 3;

Write this:

int GetUno()
{
  static int uno = 1;
  return uno;
}
int GetDos()
{
  static int dos = 1;
  return dos;
}
int GetTres()
{
  static int tres = 3;
  return tres;
}

Then use the accessor functions instead of globals.

In C/C++, there is no guarantee as to the order of construction betwixt
translation units.  This technique will guarantee order of construction
(provided you do not have a circular dependency).

HTH,
--Eljay

RE: global const variable not getting assigned properly

[John (Eljay) Love-Jensen]

Hi Chad,

When you compiled the other shared library, did you use the same version of GCC (4.0.2 or 4.1.0) that you are using for your executable?

It sounds like a compiler version mismatch of some sort.

Sincerely,
--Eljay

Re: global const variable not getting assigned properly

[Chad Scholes]

So, I have found a little more information:

I have a Shared Library.  In that library is defined a number of static classes and const variables (they are global variables).  We need them to be static and/or const so they get loaded only once and everyone can reference them.

If I create an exe and reference any of those static classes or const (defined in the Shared Library) everything is fine.  However,  If I create a shared library that then calls any of the static classes or consts (defined in the other shared library) then none of the statics or consts are initialized.

I am linking the other library at Link time with the -lsoname parameter.  Do you know why they are not getting initialized?  If I call dlopen instead will that help solve this problem?  Is there something I can set to get those initialized before I use them?

I am using g++ version 4.0.2 on Suse 10.  I also get the same results compiling with  g++ (GCC) 4.1.0 (SUSE Linux).

Thanks!!!!


>>> John Love-Jensen <eljay@adobe.com> 12/08/06 5:44 AM >>>
Hi Chad,

> Any idea why it is 0 when using wcslen?  And any idea why I'm not even getting
> an error to notify me of the problem?

Works on my platform with my version of GCC with the BSD Standard C Library
(ISO/IEC 9899:1999 compliant).

I'm guessing its either your Standard C Library or your version of GCC or
your platform.

What version of Standard C Library are you using?

Who is the provider of your Standard C Library (e.g., GLibC)?

What version of GCC are you using?

What platform are you using?

Also, your code snippet and explanation of the behavior is nice, but could
you provide a short complete code example that demonstrates the problem.
Maybe its something simple like you used the incorrect header files (e.g.,
<wchar.h> instead of <cwchar>).

And could you provide the GCC command line that you used to compile your
short complete code example.

Thanks,
--Eljay