I declare a variable unsigned char bdata Kde in a.c.
[in file a.c] unsigned char bdata Kde;
[in file b.c] #include <stdio.h> ..... extern unsigned char bdata Kde; sbit testbit=Kde^1; void main(void) {......}
Cuthbert, I see that your problem is documented and discussed on page 378 of the C51 User's Guide, User's Guide 09.2001. ...maybe it is not coincidence that I was reading that page earlier today. However, it turned out that my problem was that my sbit was being redefined and the compiler gave no warning, then optimized away all of the references to the sbit. sbit MODEM_RING = P1 ^ 4; #define MODEM_RING 0x04 // ring input My question is, why was there no warning? Another question, how do I turn off the optimizer? I tried setting it to zero but the code was still removed.
sbit MODEM_RING = P1 ^ 4; #define MODEM_RING 0x04 // ring input
Andrew, Thanks, the preprocessor listing could have exposed the problem sooner had I known about it. As far as being unable to turn off the optimizer, this seems like an undesirable idea. Why would the compiler writers have a problem with an option of NOT optimizing? I'm sure it would have saved me time earlier today. Robert
Turning off the optimizer would not have helped you at all since it did not partake in your "bug". Bypassing the C pre-processor would have yielded an error but you cannot bypass the C pre-processor. A good working knowledge of ISO C would have helped you, however.
Mark Odell writes: >Turning off the optimizer would not have helped you at all since it did not partake in your "bug". Oh, but if I had been able to turn off the optimizer I would have been able to see the constant expression that was being evaluated. This is the point as to why the optimizer was a barrier, and it seems a pointless barrier. >A good working knowledge of ISO C would have helped you, however. And your point is?...that the way it's been before is the best way? Robert
Oh, but if I had been able to turn off the optimizer I would have been able to see the constant expression that was being evaluated. I'd be pretty surprised to find any compiler that didn't remove the statement:
0x04;
Mark wrote, "A good working knowledge of ISO C would have helped you" Robert, "And your point is?..." It's not the compiler's job to pass comment on your style - if you write a valid language construct, the compiler should just generate the corresponding object. A statement like
Mark, I tried compiling
..\MAIN.C(492): warning C275: expression with possibly no effect
MOV A, #0x04 XRL A, #1 JNZ ?C0004 INC ERROR_COUNT ?0004:
Mark, You wrote, >Sticking to convention might have proved more helpful, e.g. only MANIFEST_CONSTANTS and ENUMS are uppercase. I'm not sure what you mean by "MANIFEST_CONSTANTS and ENUMS". I suppose that this means to use uppercase for the #defines, and lowercase for the sbits. I see now that had this style been in use in the code I was working with this morning, this discussion would not be occurring. This may also explain the penchant of C programmers to remove uppercase from everything else, including URLs: fear of the preprocessor! Personally, I have never gotten used to seeing lowercase hex digits, which I first saw done in the C community. I've also noticed that C programmers tend to hack DOS filenames into lowercase. For the bigger picture, I think that the standard remains English. Robert
"This may also explain the penchant of C programmers to remove uppercase from everything else, including URLs: fear of the preprocessor!" Actually, it's more likely to be those with a UNIX background - but then 'C' and UNIX are very closely linked! However, some parts of the internet (including some webservers) are case-sensitive (probably mostly the UNIX bits!) - so it's not always safe to fiddle with the capitalisation of a URL, E-Mail address, etc "I suppose that this means to use uppercase for the #defines" Yes, that is the convention. Preprocessor definitions can behave quite differently to 'C' symbols - especially concerning side-effects etc - therefore it is particularly valuable to have your Preprocessor definitions instantly distinguishable, to help avoid the common pitfalls (see any good 'C' book)
I'm not sure what you mean by "MANIFEST_CONSTANTS and ENUMS". A manifest constant is a #define an enums are enumerated integer constants as you guessed. The uppercase I used here was to indicate that they are conventionally written in uppercase. Variables are not. The pre-processor does not remove uppercase and uppercase hex digits have nothing to do with manifest constants or enums. Also, we convert all filenames to lower case since some OS's are case sensitive and since certain OS's don't care it makes it easier to deal with one standard. I had a problem with one developer on Linux that could not build my sources which I could build fine on Windows 2000. I had included a file as #include "FooBar.h" but when the file was committed to the CVS repository it ended up as foobar.h. When the Linux compiler attempted a case sensitive match for FooBar.h it could not find it and barfed. I have a C coding standard a my website that I invite you to browse to see what makes me tick on this subject. Also, I have some 8051 code samples there too. Enjoy! http://www.embeddedfw.com
Sorry, but your coding convention document is marked "confidential".
Ignore it. It's not confidential, I'm just too lazy to remove it and reprint the PDF. Apologies.
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