One issue – ISO C defines setvbuf (configure buffer mode and size of a stdio stream) but not getvbuf (get current buffer mode and size). On many platforms with

One issue – ISO C defines setvbuf (configure buffer mode and size of a stdio stream) but not getvbuf (get current buffer mode and size). On many platforms with non-opaque FILE, you can implement your own getvbuf by peering inside its undocumented fields. I guess part of why it is not in the standard is that it is rarely requested functionality, but there are rare use cases where it may have value. And I think it is an unfortunate lack of orthogonality to have a setter but no corresponding getter. stdio_ext.h offers some functionality like a "getvbuf", but not quite – e.g. __fbufsize tells you a stream's buffer size, and __flbf whether it is line-buffered – but it isn't clear how to distinguish fully buffered and unbuffered streams. And stdio_ext.h has never been standardised, it is an extension invented on Solaris and copied by Linux (and a few other platforms too, e.g. IBM z/OS).