Application Fails if Lib not found, anyway to avoid this?

KillerCode · 01-02-2011, 05:09 PM

i was wondering if there is away to avoid application from closing if a specific library not found?

for example: if my application uses libPng and it wasn't found on the system running my app (binary and not source), is there anyway to just disable the part that uses png from my application?

thanks;

MS3FGX · 01-02-2011, 05:12 PM

It is kind of hard for us to tell you what libraries your application does or does not need. If your application doesn't need libpng, then don't link against it. If your code requires the functionality of libpng, then there isn't much you can do about it.

Sergei Steshenko · 01-02-2011, 05:17 PM

Quote:

Originally Posted by MS3FGX

It is kind of hard for us to tell you what libraries your application does or does not need. If your application doesn't need libpng, then don't link against it. If your code requires the functionality of libpng, then there isn't much you can do about it.

Well, not quite. If the application can deal with other than PNG formats, and if the application is using dynamic libraries ( .so files under Linux), the the application can check library existence before using its functions:

man 3 dlopen

and friends, also look up

GNU libtool

which has convenient cross-platform wrappers and somewhat abstracts out linking.

KillerCode · 01-02-2011, 05:25 PM

@MS3FGX: i know what libraries it uses, but the problem is, if those libraries arent found on user pc the whole application wont start, im looking for away so it starts and just disable the part that uses this library

@Sergei Steshenko: are those dlopen and dlsym are like windows LoadLibrary and GetProcAddress? (Load a library and get its handle, and then find procedure addresses through this handle?

dugan · 01-02-2011, 05:40 PM

There is in Python. In Python, you get an exception if a given library is not found. You can catch the exception and branch as appropriate.

Linux C/C++ programs resolve this at compile-time, using GNU Autotools. Or, you can link libpng statically.

Sergei Steshenko · 01-02-2011, 06:01 PM

Quote:

Originally Posted by KillerCode

...
@Sergei Steshenko: are those dlopen and dlsym are like windows LoadLibrary and GetProcAddress? (Load a library and get its handle, and then find procedure addresses through this handle?

I don't know Windows programming; 'libtool' abstracts the details out, i.e. your code looks the same for both Windows and UNIXish systems, I think that even library file names can be forced to look the same rather than to have .so or .dll extensions.

KillerCode · 01-02-2011, 06:03 PM

im gonna try now
thx all for the great help

KillerCode · 01-07-2011, 01:02 AM

i know its kinda late to post results, but, actually dlopen, dlsym, dlerror and all those require a library too :/ -ldl have to link dl library to that

is there anyway to avoid that? cause if it's not found, my app will still fail :S

graemef · 01-07-2011, 01:55 AM

Try linking your essential libraries statically.

KillerCode · 01-07-2011, 05:43 AM

is that different from -l command under gcc?

graemef · 01-07-2011, 06:21 AM

you might want to google gcc linker options and look up the -static switch

wje_lq · 01-07-2011, 06:22 AM

Quote:

Originally Posted by KillerCode

is that different from -l command under gcc?

I don't know what "-l command under gcc" means. As far as I know, gcc does not have a -l option. But graemef is referring to the -static option under gcc.

graemef · 01-07-2011, 06:33 AM

Quote:

Originally Posted by wje_lq

I don't know what "-l command under gcc" means. As far as I know, gcc does not have a -l option.

The option -llibrary will link the library named library but the default is to do it dynamically, if possible.

linker options

wje_lq · 01-07-2011, 07:49 AM

Quote:

Originally Posted by graemef

The option -llibrary will link the library named library

D'oh! I knew that! :(

KillerCode · 01-07-2011, 09:54 AM

Code:

-static
On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect.

i still got no idea what that means?? does it mean that the library will be part of my application? both will be 1 file?