Enrico Weigelt <weigelt@xxxxxxxx> writes: > What does the ANSI C spec say about the "register" keyword ? 6.7.1. "A declaration of an identifier for an object with storage-class specifier register suggests that access to the object be as fast as possible. The extent to which such suggestions are effective is implementation-defined." Then a footnote to that text says "The implementation may treat any register declaration simply as an auto declaration. However, whether or not addressable storage is actually used, the address of any part of an object declared with storage-class specifier register cannot be computed, either explicitly (by use of the unary & operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in 6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier register is sizeof." > Does GCC issue some warning when it fails to put such a variable > directly into a register ? No. > Is it that keyword still useful at all on todays compilers ? No, except for things like gcc's extension to specify the hardware register where a variable should live. > I'm not really experienced at that low level, but i can imagine > scenarios where it's essential to keep certain things in registers > (eg. when there's no valid stack), so the compiler should issue > a warning (which can be made fatal w/ -Werror) in those cases. Such code can not be written in standard C. It always requires extensions. Ian
