Anonymous union inside a struct?

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Read-Only Author Sam Liggin Posted 30-Nov-2001 17:11 GMT Toolset C166	Anonymous union inside a struct? Sam Liggin The C complier doesn't like this piece of source code: ------------------------- struct MyUart { union { unsigned char rx; // read unsigned char tx; // write }; unsigned char control; // r/w }; volatile struct MyUart far* const UART = 0x101010; unsigned char ReadByte( void ) { while ( (UART->control & 0x01) == 0 ) {} return UART->rx; } -------------------- I get the following error: UNION.C(15): error C70: rx: undefined member However, I get no error at line #13 on the reference to UART->control. Is there something I'm overlooking?

Read-Only Author Mike Kleshov Posted 1-Dec-2001 16:07 GMT Toolset C166	RE: Anonymous union inside a struct? Mike Kleshov I don't have the C standard within my reach at the moment, but I'm pretty sure that anonymous unions were introduced in C++, not in C. So there is an obvious way of making the piece of code work: struct MyUart { union { unsigned char rx; // read unsigned char tx; // write } data; unsigned char control; // r/w }; volatile struct MyUart far* const UART = 0x101010; unsigned char ReadByte( void ) { while ( (UART->control & 0x01) == 0 ) ; return UART->data.rx; } Another thing to be concerned about is alignment of structure members in memory. By default, they are aligned at word boundaries. Regards, Mike

Read-Only Author Norbert Paul Posted 4-Dec-2001 14:49 GMT Toolset C166	RE: Anonymous union inside a struct? Norbert Paul Anonymous unions and structures are a Microsoft specific extension to C++. They are not even defined in standard C++.

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