An excellent white paper on the shapefile format is available from ESRI, but it is .pdf format, so you will need Adobe Acrobat to browse it. Shapelib is hosted at shapelib.maptools.org. A mailing list for discussion of how to use shapelib, and announcing new releases is available. To only find out about new releases of Shapelib select the ‘Subscribe to new releases’ option from the link at Freshmeat. Care should also be taken to pass the binary access flag into SHPOpen() and DBFOpen() when operating on systems with special text file translation such as MSDOS. The shputils.c module is contributed, and may not take the same approach to portability as the rest of the package. On Linux, and most unix systems it should be possible to build and install shapefile support as a shared library using the ‘lib’ and ‘lib_install’ targets of the Makefile. Note that this Makefile doesn’t use autoconf mechanisms and will generally require some hand tailoring for your environment. Source.