Not able to link shared library.

pradiptart · 06-14-2012, 12:51 AM

Hi all,

I am building my application.I have 10 cpp files and I made one make file to compile those .My problem is that my application is dependent upon some library that i have to put in some directory.

for example i am storing my library as follow
here i am storing 2 libraries
1st in /opt/my_lib_root
2nd in /opt/my_lib_root/my_lib/

but when my application running it showing

error while loading shared libraries: libproduct.so.1: cannot open shared object file: No such file or directory as I am depending upon this library and it is the 1st library.

I know it is not linked properly ,when i am using

export LD_LIBRARY_PATH=/opt/my_lib_root/my_lib/:/opt/my_lib_root/
it is working.

but i don't want to do in mannualy how to mentioned this one during compilation of the project.

During compilation how to do this or is there any solution for these linking error.

Thanks

pan64 · 06-14-2012, 03:33 AM

this is the normal behavior, it is not an error. A shared object (*.so file) usually located in /usr/lib or /lib and in your case the file is located in another dir, that's why you need to use LD_LIBRARY_PATH. Another solution can be to hardcode the path of that lib into your app. This can be made by linking this lib with full path to your app.

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pradiptart · 06-14-2012, 04:36 AM

Hi pan64 ,
Thanks for reply.

Quote:

Another solution can be to hardcode the path of that lib into your app. This can be made by linking this lib with full path to your app.

can u say how to hardcode this and where.

Thanks

pan64 · 06-14-2012, 04:48 AM

do you have a makefile? can you post it?

pradiptart · 06-18-2012, 05:24 AM

Hi pan64,

I got your point,
I have tried something like -rpath and able to link it and run it but now I got another issue.
The issue is I am creating a RPM of the application so in the spec file only I am deciding where to put the libraries, which is not same as the path I have given during compilation in -rpath so,the problem is when it is running,the path of library is different and it is not running now so can u tell me how to resolve this error ,

as I don't know where the library will be as first compilation done then only the RPM creation done then how i will able to run this applications as library path is different now.

Kindly tell me this is a serious issue I am facing in my project work.

giving an example:

suppose I am working in /root/work/ folder and the makefile is here and all the source is here.all libraries are in /root/work_lib/ that I know during compilation and able to link this library during compilation,and able to run this
but during RPM creation I am deciding where to put the libraries of the RPM and that is different from this /root/work_lib/ and also that is variable depends upon the reqirements of projects ,so how do i able to make this application that will work after the RPM creation.

to this problem I got the old style LD_LIBRARY_PATH environment variable that I have to set in RPM spec file but is that the only one solution is there any other solution to this problem.

Thanks

pan64 · 06-18-2012, 06:28 AM

in such cases probably you can write a small shell script to set LD_LIBRARY_PATH and invoke your tool. Also you can use relative path during link: (instead of -L <path> -l <lib> simply write ../lib_dir/libsomething.so). In this case the app will look for the lib in ../lib_dir (which is probably not really good, but you can decide). You can try dynamic loader also to load a library.

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If someone helps you, or you approve of what's posted, click the "Add to Reputation" button, on the left of the post.
Happy with solution ... mark as SOLVED
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pradiptart · 06-18-2012, 08:26 AM

hi ,
As you told dynamic loader,dlopen() function needs the library path that i can't give during compilation.
The problem is how to use the path that I do not know during compilation ,so I can't do any thing during compilation.
simply I have to build the RPM and then I have to do something by which the application should find the libraries.

The solutions to this problem are as follows

solutions
1.LD_LIBRARY_PATH
2?
3?

I need the other possible ways to do this.kindly tell about that .

Thanks

414N · 06-18-2012, 08:33 AM

Why don't you put the library inside a default path, like /usr/lib, /usr/local/lib etc.?
This way all your issues should be solved with no need for rpath and LD_LIBRARY_PATH...

pan64 · 06-18-2012, 08:36 AM

Quote:

void *dlopen(const char *filename, int flag);
The function dlopen() loads the dynamic library file named by the null-terminated string filename and returns an opaque "handle" for the dynamic library. If filename is NULL, then the returned handle is for the main program. If filename contains a slash ("/"), then it is interpreted as a (relative or absolute) pathname. Otherwise, the dynamic linker searches for the library

If you describe the filename with full path that will be used.
LD_LIBRARY_PATH can be set with a small wrapper script which will look for the lib and set the variable before executing your app. Both can work runtime, so in both cases they can use the path of the installed package.