I have developed an extensive library of C routines for the manipulation of protein structures. The routines are extensively documented within the code, but no separate documentation is currently available. The routines include reading and writing of PDB and CSSR files, rotation, translation, resequencing, calculations, fitting, adding hydrogens, ordering, sequence reading and alignment, etc., etc.
In addition, I have a library of more general purpose C routines. These include error handling, 2D arrays, FORTRAN-style rigid column input, text manipulation, help file handling, HPGL and PostScript plotting, command parsing, etc.
An HTML summary of all the routines is available here.
Include files for these are found in ~martin/include/bioplib (where the source is also stored) and the link libraries are in ~martin/lib.
If you are outside the BSM unit at UCL, you should obtain a licence form as a PostScript or PDF file. Make 2 copies and complete both: keep one for yourself and return the other by post to the address on the form.