I run into a problem using enum datatype with printf statement. The folloing code works with Viusal C but does not work with KEIL compiler --- printf statement prints out the wrong value. Could somebody in this forum tell me what I did wrong here? --- here is the test code
enum MONTHS {JAN=1,FEB,MAR,APR,MAY,JUN,JUL, AUG,SEP,OCT,NOV,DEC} birthday; void main(void) { birthday = NOV; printf("\n\r\ My birthday = %d", birthday); }
"Could somebody in this forum tell me what I did wrong here?" You assumed that you could just take any piece of 'C' code from one compiler to another without any consideration of the implementation-specific issues. In particular, you have taken code from a large 32-bit desktop system and dumped it onto a small, specialist embedded 8-bit target! http://www.8052.com/forum/read.phtml?id=110880
Per the ANSI standard, a C "int" has to be at least 16 bits wide. An 8-bit processor would naturally prefer 8-bit values where possible. Keil C51 has a few extensions to allow you to use 8 bit values for greater efficiency. One of these extensions means that they do not automatically "promote" 8-bit values to "ints" when passed as parameters. (See "ANSI integer promotion" in the manual.) As a result, a variable-arg function like printf() needs a format specifier for a value that's 8 bits wide, and not just for ints. %d is the standard format specifier for an int (decimal). %ld is the standard format specifier for a "long int". This lets printf() know that the amount of data in the parameter list is perhaps longer than just for a %d int. %bd is the Keil format specifier for a "byte int". This lets printf() know that the amount of data in the parameter list is less than that for a %d int. If you tell printf that there's a %d in the parameters, but actually pass in a 8-bit value, the print routine will pull out two bytes, not just one, and all the printed data gets misaligned and comes out garbled.