Linking libpng with g++.

Question

I'm trying to get libpng working on linux. I couldn't get it to work through netbeans, so I ran g++ directly as g++ -lpng -lz main.cpp -o test and it compiles. When I try to run it it it outputs ./test: error while loading shared libraries: libpng14.so.14: cannot open shared object file: No such file or directory. I assume this means I am linking dynamically and it can't find the .so file

~/Programs/NetBeansProjects/DiamondSquare$ ldd test linux-gate.so.1 => (0x008a5000) libpng14.so.14 => not found libz.so.1 => /usr/local/lib/libz.so.1 (0x00209000) libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x0094b000) libm.so.6 => /lib/tls/i686/cmov/libm.so.6 (0x00e3a000) libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00927000) libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0x00220000) /lib/ld-linux.so.2 (0x00b85000)

I didn't really want to link dynamically in the first place. How could I resolve this?

I know that libpng14.so.14 is in /usr/local/lib also, if that matters.

Extra points if you can tell me how to do this within netbeans.

Answer 1

Dynamic linking is the default and should be preferred in general. You say libpng is in /usr/local/lib, are you really positive about this? It finds /usr/local/lib/libz.so.1. If libpng14.so.14 was in /usr/local/lib, too it should find it.

Answer 2

It's odd that g++ is able to find the library but test can not (you can tell that g++ can find it because test specifically expect libpn14 even though you only tell g++ '-lpng'). Are you sure you aren't passing any -L or -R flags to g++? Are your LD_PRELOAD or LD_LIBRARY_PATH environment variables set in the shell you're running g++ in but not in the shell you're running test in? You can point LD_PRELOAD at a specific shared library to tell an app or g++ how to find it, and any folders in LD_LIBRARY_PATH are automatically searched.

Also to link libpng statically put "-Wl,-Bstatic" before "-lpng." Beware, any libraries after the -Bstatic will be linked statically. You can switch back to dynamic and list some more libraries by using "-Wl,-Bdynamic -lfoo".