Microchip bending the rules of C?

Question

I was digging through some headder files relating to a PIC microcontroller when I came accross a load of structs that look like this:

typedef struct tagPORTDBITS {
  unsigned RD0:1;
  unsigned RD1:1;
  unsigned RD2:1;
  unsigned RD3:1;
  unsigned RD4:1;
  unsigned RD5:1;
  unsigned RD6:1;
  unsigned RD7:1;
  unsigned RD8:1;
  unsigned RD9:1;
  unsigned RD10:1;
  unsigned RD11:1;
  unsigned RD12:1;
  unsigned RD13:1;
  unsigned RD14:1;
  unsigned RD15:1;
} PORTDBITS;

Is this standard C? I cant find any other referances to anything that looks like this, ie with the ":1" after the variable definition

I assume all the elements are representing bits, so is this a Microchip addition to their C compiler to make things easier for embeded programmers?

Answer 1

This is a C bitfield , which is a perfectly valid (although unportable) construct. See here or here for more info.

Although the data layout in a bitfield is implementation-defined and therefore unportable, they are often used in embedded processing to map individual bits of a register to logical names. This works because most embedded processors use their own specific toolchain where the bitfield layout rules are well understood.

Answer 2

是的，这是标准C.这个名称是位字段 。

Answer 3

This is standard C. It is called a bit-field

This struct definition is commonly used for exactly what you provided as example: Making bitwise data communication more easy to read, because you can then access single bits easily with a name instead of shifting or bitwise operations and struggling around with bytes, while still having the ability to use the data directly as a single integer or byte.