Editing Software Development Platforms (section)

===Working with Objects and Libaries===

Here are some useful commands that generally work on Linux or OS-X.

To check what type a certain file is, use the <tt>file</tt> command.  For example

 $ file libvtkmyUnsorted.so
 libvtkmyUnsorted.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, not stripped

Notice that we get a lot of information about this object.  On systems with both 32 bit and 64 bit objects (such as OS-X) this can be particularly useful to see how this was compiled.

To list the symbols in an <tt>.o</tt> or <tt>.so</tt> or <tt>.a</tt> file, use <tt>nm</tt>.  This can be useful to see if a particular function is available in a particular object or library.  There can be a lot of output from this command, so typically you might dump the output into a file and then search that file using your preferred text editor.

To find out which shared libraries an executable or library will want to load at run time, use <tt>ldd</tt>.  (On OS-X, a similar tool is <tt>otool -L</tt>.)  For example

 $ ldd faim_d 
 	linux-vdso.so.1 =>  (0x00007fff077aa000)
 	libcgiter.so => not found
 	liblapack.so.3gf => /usr/lib/atlas/liblapack.so.3gf (0x00007f4b7a295000)
 	libpthread.so.0 => /lib/libpthread.so.0 (0x00007f4b7a079000)
 	libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007f4b79d6c000)
 	libgfortran.so.3 => /usr/lib/libgfortran.so.3 (0x00007f4b79a90000)
 	libm.so.6 => /lib/libm.so.6 (0x00007f4b7980b000)
 	libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00007f4b795f3000)
 	libc.so.6 => /lib/libc.so.6 (0x00007f4b79281000)
 	libblas.so.3gf => /usr/lib/atlas/libblas.so.3gf (0x00007f4b788c4000)
 	/lib64/ld-linux-x86-64.so.2 (0x00007f4b7ad80000)

Notice that in this example it is telling us that <tt>faim_d</tt> will need to load libcgiter.so, but that it can't be found.  We can fix this by adding the path to libcgiter.so to LD_LIBRARY_PATH (or on OS-X, to DYLD_LIBRARY_PATH).


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