C17 (C standard revision)

C17, formally ISO/IEC 9899:2018, is an open standard for the C programming language, prepared in 2017 and published on 5 July 2018. It replaced C11 (standard ISO/IEC 9899:2011), and is superseded by C23 (ISO/IEC 9899:2024) since October 2024. Since it was under development in 2017, and officially published in 2018, C17 is sometimes referred to as C18.

Changes from C11

C17 fixes numerous minor defects in C11 without introducing new language features.

The <code>__STDC_VERSION__</code> macro is increased to the value <code>201710L</code>.

For a detailed list of changes from the previous standard, see Clarification Request Summary for C11. Examples of changes include fixes for <code>#elif</code>, <code>realloc</code>, and typos, among others.

Compiler support

List of compilers supporting C17:

• GCC 8.1.0
• LLVM Clang 7.0.0
• IAR EWARM v8.40.1
• Microsoft Visual C++ VS 2019 (16.8)
• Pelles C 9.00

See also

• Compatibility of C and C++
• Outline of the C programming language

References

Further reading

• N2176 (final draft of C17 standard); WG14; 2017-10-09.

• N2310 (post-C17, very early draft of what would become C23; WG14; 2018-11-11.
• ISO/IEC 9899:2018 (official C17 standard); ISO; 2018.

External links

• C Language WG14 (Working Group 14)

* C Language Working Group 14 (WG14) Documents

* C Language WG14 page, as it appeared on 2018-07-22, just after the publication of C17