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C51 warning C322: unknown identifier

Robert Wilcox

I am porting some code to 8051 and the existing code uses #define to determine whether or not some functionality is available

i.e. ....

#define HAVE_STRING_H
.
.
.
.

#ifndef HAVE_STRING_H
#include <string.H
#else
#include <homegrown/string.h>
#endif
Any suggestions on how I can suppress or correct C322?

Obviously, I can change
#define HAVE_STRING_H
to
#define HAVE_STRING_H 1
and then change
#ifdef HAVE_STRING_H
to
#if HAVE_STRING_H
but I am trying to preserve as much of the original code as I can.

Any help is appreciated and thanks in advance.

Robert

Parents
  • 0 in reply to Drew Davis

    "I'm more a fan of the ANSI style"

    Yes, me too.

    I notice that modern compilers seem to deal sensibly with this:

    #if SYMBOL
    ...
    #endif

    If SYMBOL has not been defined you get an 'undefined symbol' error.

    At least one ancient compiler I use from time to time treats SYMBOL as false in this situation, which is a real nuisance.

    Stefan

Reply
  • 0 in reply to Drew Davis

    "I'm more a fan of the ANSI style"

    Yes, me too.

    I notice that modern compilers seem to deal sensibly with this:

    #if SYMBOL
    ...
    #endif

    If SYMBOL has not been defined you get an 'undefined symbol' error.

    At least one ancient compiler I use from time to time treats SYMBOL as false in this situation, which is a real nuisance.

    Stefan

Children
  • 0 in reply to John Donaldson

    "If SYMBOL has not been defined you get an 'undefined symbol' error."

    Not with an ANSI/ISO compliant compiler. If an undefined macro name appears in the constant-expression of #if or #elif, it is replaced by the integer constant 0.

  • 0 in reply to Dan Henry

    "Not with an ANSI/ISO compliant compiler. If an undefined macro name appears in the constant-expression of #if or #elif, it is replaced by the integer constant 0."

    Well there you go, I'd never realised that was supposed to happen. I realise now that the modern compilers I use issue a warning rather than an error (making them compliant - I understand that 'Warning: Cup of tea required at line 37' is permitted by the standard).

    In this case it seems very sensible to issue a warning...

    Stefan

  • 0 in reply to John Donaldson

    I'd never realised [undefined substituted with 0] was supposed to happen

    Good ol' K&R behavior. It helps contribute to the popular trap when people try to use the conditionals with nice readable string values instead of integers:

    -DPLATFORM=EVAL

    #if PLATFORM == EVAL
    #elif PLATFORM == SIM
    #endif

    Works like a charm, since PLATFORM becomes EVAL, and then EVAL on both sides of the first == becomes 0. 0 == 0, so off you go with the first branch, even if you -DPLATFORM=SIM. A warning can be a good thing.

    (You can actually make this work if you #define a series of constants for EVAL, SIM, etc., in a header, and are sure to include that header.)