C17, formally ISO/IEC 9899:2018,[1] is an open standard for the C programming language, prepared in 2017 and published in July 2018. It replaced C11 (standard ISO/IEC 9899:2011),[2] and is superseded by C23 (ISO/IEC 9899:2024) since October 2024.[3] Since it was under development in 2017, and officially published in 2018, C17 is sometimes referred to as C18.[4]
Changes from C11
C17 fixes numerous minor defects in C11 without introducing new language features.[2]
The __STDC_VERSION__ macro is increased to the value 201710L.
For a detailed list of changes from the previous standard, see Clarification Request Summary for C11.[5]