Published ISO and IEC standards can be purchased from a member body of ISO or IEC.
The latest publically available version of the C11 standard is the document WG14 N1570, dated 2011-04-12. This is a WG14 working paper, but it reflects what was to become the standard at the time of issue.
The previous standard for Programming Language C (C99) is ISO/IEC 9899:1999, published 1999-12-01.
Technical Corrigendum 1 (ISO/IEC 9899:1999 Cor. 1:2001(E)) was published in 2001 (additional documentation).
Technical Corrigendum 2 (ISO/IEC 9899:1999 Cor. 2:2004(E)) was published in 2004.
Technical Corrigendum 3 (ISO/IEC 9899:1999 Cor. 3:2007(E)) was published in 2007. It can be obtained free of charge from ISO.
The latest publicly available version of the C99 standard is the combined C99 + TC1 + TC2 + TC3, WG14 N1256, dated 2007-09-07. This is a WG14 working paper, but it reflects the consolidated standard at the time of issue.
The rationale for the C99 standard is available.
The 1990 ISO standard (now outdated) consisted of the following:
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