C dialect options

Language

August 01, 2022

Ref: 1, 2

ISO C90	ISO C99
-ansi, -std=c89, iso9899:1990, (ISO C90)	-std=c99, iso9899:1999
-std=iso9899:199409 (ISO C90 as modified in amendment 1)	-std=gnu99 (iso c99 + gnu extensions, gcc default)
-std=gnu89 (iso c90 + gnu extensions + some c99 features)

ISO C11	ISO C18
-std=c11	-std=c17, -std=c18

iso9899 (C Lang Spec Number of ISO)
-ansi for C++ mode means that remove conflics gnu extensions with ISO C++
The word ansi means American Nation Standard Institute, c89 means ansi 89 (the first standard version), however c99 is iso 1999.The history is ansi89 -> iso90(same with ansi89) -> iso99, in other words, iso take the ownership of the C Lang standard from ansi.
c18 is created on 2017 and released on 2018, so it’s called c17 or c18. It contains no new features, just corrections

Runtime Environments

std	no_std
-fhosted (takes place in a hosted env)	-fno-hosted
-fno-freestanding	-ffreestanding
-fno-builtin, -fno-builtin-

fno-builtin: Don’t recognize built-in functions that do not begin with __builtin_ as prefix, __built_in_xxx always existed.
fno-builtin- such as `-fno-builtin-printf`.
on no_std env using __builtin_xxx instead