How to do this with a pretend zlib path -- you need to change it to whatever code you are trying to run in your C/C++ code. C examples:

1. you have to get the header files into your code
Steps:

A. gcc -I /path/to/zlib # when compiling. This adds a directory to the include search path
B. In your C code you have to include the "foreign" header file just like you would do for standard C header files:

Code:

#include <zlib.h>

2. You have to use -L path/to/zlib/libraries also on the gcc command line. To compile:

Code:

gcc -mycode.c -I /path/to/zlib/headers -L /path/to/zlib/shared_libraries

3. Finally you need to have added (or created) an environment variable LD_LIBRARY_PATH which knows where the special shared libraries live on a particular system.

Code:

export LD_LIBRARY_PATH={$LD_LIBRARY_PATH}:/path/to/zlib/shared_libraries

This has to be there (along with the zlib shared libraries in a directory) on every system
you want to run you code one. This is the biggest source of error for this kind of development.
You can find it because the ldd command does not know where zlib libraries are - meaning at runtime the link and run step fails. Which creates all kinds of user complaints and problems. This variable has to be created everywhere for every user who will execute the code. The LD_LIBRARY_PATH definition systemwide .profile file is a possible choice, it may have security issues.