Resources for Portable Programming

• C99 standard (technically a final draft: currently unavailable, but this appears to be a corrected version). And its rationale.
• C11 standard (technically a final draft), and an overview of the changes.
• Fortran standards, including links to the F77 as well as the correct layout of Fortran 77 subprograms. Final draft standards are available for F90 and F2003.
• ftnchek, a program to check against Fortran standards.
• POSIX 1003 standards (2008, revised 2016): how Unix-alike functions and tools are to behave. (2004 edition).
• Porting to 64 bit GNU/Linux systems. Covers a lot of details about 64- vs 32-bit architectures.
• The self-styled Filesystem Hierarchy Standard. Not written to the standard of a standard, but Debian Linux policy.
• How to write shared libraries. Lots of information on GCC 4.0.0 features, including controlling symbol visibility as implemented in R 2.3.0.
• mudflap. A bounds-checking (etc) tool for GCC 4.
• Valgrind. A debugging tool for ix86 Linux. (See also `Writing R Extensions'.)
• GCC Links and selected readings
• What Every Computer Scientist Should Know about Floating-Point Arithmetic by David Goldberg, including Doug Priest's supplement on extended-precision systems (such as ix86).
• FreeBSD's collection of man pages (including for some commercial Unixes). And more from *nixDoc.
• Jan Walter's Unix incompatibility notes. Not 100% reliable (please don't pretest isalpha by isascii, for example).