Reference: https://lists.gnu.org/archive/html/bug-ddrescue/2019-05/msg00000.html https://lists.gnu.org/archive/html/bug-ddrescue/2019-05/msg00001.html Basically, these functions are defined as macros and not being included in std. If compiling with GCC libstdcpp, it works because internally, the header #undefs these functions. This is not the case with uClibc++(or maybe some other libc++).