Linking/Deferred linking for binary packages

libfoo.so may be distributed as a binary package and app.c foo.h would be distributed as source-code and built on the clients. libfoo.so has unresolved references which is resolved when building app on the client.

This helps with two problems:

1. Library versions, if a library has changed its version number but the change is ABI compatible with libfoo.so a simple rebuild of app will resolve this (just as rebuilding source-based packages)
2. Library path issues, some distributions place libraries in non-standard locations and maybe a dependency is installed by the user in their home-directory. This can also be fixed using symlinks or by fiddling with LD_LIBRARY_PATH but deferred linking is better in long term.

Code: app.c (view, download)

1. #include "foo.h"
2.  
3. int main(int argc, const char* argv[]){
4.   return real_main(argc, argv);
5. }

Code: foo.h (view, download)

1. #ifndef __FOO_H
2. #define __FOO_H
3.  
4. int real_main(int argc, const char* argv[]);
5.  
6. #endif /* __FOO_H */

Code: foo.c (view, download)

1. #include "foo.h"
2. #include <stdio.h>
3. #include <jpeglib.h>
4.  
5. int real_main(int argc, const char* argv[]){
6.   printf("in real_main\n");
7.  
8.   struct jpeg_compress_struct cinfo;
9.   struct jpeg_error_mgr jerr;
10.  
11.   cinfo.err = jpeg_std_error(&jerr);
12.   jpeg_create_compress(&cinfo);
13.  
14.   return 0;
15. }

Code: Makefile (view, download)

1. all: app
2.  
3. libfoo.so: CFLAGS+=-fPIC
4.  
5. libfoo.so: foo.o
6.         $(CC) -shared $(LDFLAGS) foo.o -o libfoo.so
7.  
8. app: app.o libfoo.so
9.         $(CC) $(LDFLAGS) app.o -Wl,-rpath,. -L. -lfoo -ljpeg -o app
10.  
11. %.o : %.c
12.         $(CC) -Wall $(CFLAGS) -c $< -o $@
13.  
14. clean:
15.         rm -rf *.so *.o app