C17 is the informal name for ISO/IEC 9899:2018, the most recent standard for the C programming language, prepared in 2017 and published in June 2018. It replaced C11 (standard ISO/IEC 9899:2011). C17 will be superseded by C2x. Since it was under development in 2017, and officially published in 2018, C17 is also commonly referred to as C18. GCC, for example, treats the commands -std=c17 and -std=c18 as equivalent, and the C-Standard page on the ISO-9899 wiki refers to ISO/IEC 9899:2018 as C18, only noting later that the standard is sometimes called C17.