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In <26854@netnews.upenn.edu> weisen@eniac.seas.upenn.edu (Neil Weisenfeld)
writes:

>Why does the following segment of code give a conversion between
>integral types warning under MSC6.00?

>#define ACTUAL_SPACE ' '
>void strmem(char *mem, char *str, int n)
>{
>  if (str && mem)
>    while (n--)
>       *mem++=(*str)?(*str++):ACTUAL_SPACE;
>}

>The *mem++= line gets the error.  Since everything is a char, I'm not
>sure what the problem is.         ^^^^^^^^^^^^^^^^^^^^^^^^^^

Guess again.  Everything -isn't- a char.  Specifically, the character
constant ' ' has as its type -int- whose value is the code for the
corresponding character in the target character set (32 decimal in
ASCII).

I've never used MSC 6.0, but I'd assume that its warning you about 
the implicit conversion of this int value to the char value on the
left hand side of the assignment above (*mem++).  Since, by definition,
the value of a character constant expression is representable as a
char, so you can safely ignore the "warning".  On the other hand, since
ignoring compiler warning messages is a bad habit to fall into, you can
cast the character constant as a char in the assignment:

        *mem++ = ( *str ) ? *str++ : (char)ACTUAL_SPACE;

(Note:  you -could- do this cast in the #define line as:

        #define  ACTUAL_SPACE  (char)' '

but there may be places in the code where ACTUAL_SPACE is used in an
int context.)
-- 
Norm Joseph                       //   Internet: cgh!amanue!oglvee!norm@dsi.com
Oglevee Computer Systems, Inc.    //       Uucp: {pitt,cgh}!amanue!oglvee!norm
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-- 
Norm Joseph                       //   Internet: cgh!amanue!oglvee!norm@dsi.com
Oglevee Computer Systems, Inc.    //       Uucp: {pitt,cgh}!amanue!oglvee!norm
            -- "Whaddya mean he had bullet holes in his mirror?" --

In article <26854@netnews.upenn.edu>, weisen@eniac.seas.upenn.edu (Neil Weisenfeld) writes:
>       *mem++=(*str)?(*str++):ACTUAL_SPACE;
> 
> The *mem++= line gets the error.  Since everything is a char, I'm not
> sure what the problem is.

K&R Classic p. 39 "...every char in an expression is automatically
converted to and int."  Casting ACTUAL_SPACE to char should clear up
the warning.

Stephen Coy
uw-beaver!ssc-vax!coy

			Brain dead is forever.

In article <26854@netnews.upenn.edu> weisen@eniac.seas.upenn.edu (Neil Weisenfeld) writes:
>Maybe I should read K&R a little more thoroughly before posting this, but...
>
>Why does the following segment of code give a conversion between
>integral types warning under MSC6.00?
>
>void strmem(char *mem, char *str, int n)
>{
>  if (str && mem)
>    while (n--)
>      *mem++=(*str)?(*str++):ACTUAL_SPACE;
>}
>
>where ACTUAL_SPACE is defined:
>
>#define ACTUAL_SPACE ' '
>

    The ? operator evaluates as type int unless explicity cast.  When in
doubt as to the source of a warning, try putting each component of the
statement on a different line:

      *mem++=
(*str)?
(*str++):
ACTUAL_SPACE;
-- 
 _
Kevin D. Quitt         demott!kdq   kdq@demott.com
DeMott Electronics Co. 14707 Keswick St.   Van Nuys, CA 91405-1266
VOICE (818) 988-4975   FAX (818) 997-1190  MODEM (818) 997-4496 PEP last

                96.37% of all statistics are made up.

weisen@eniac.seas.upenn.edu (Neil Weisenfeld) writes:

>Maybe I should read K&R a little more thoroughly before posting this, but...

Yes.

>Why does the following segment of code give a conversion between
>integral types warning under MSC6.00?
>#define ACTUAL_SPACE ' '
>      *mem++=(*str)?(*str++):ACTUAL_SPACE;

The type of a character constant (' ' in your example) is int, not char.
Hence the left side of the colon is type char and the right side is int.
The compiler is correct in issuing the warning.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com

In article <26854@netnews.upenn.edu> weisen@eniac.seas.upenn.edu (Neil Weisenfeld) writes:
>Why does the following segment of code give a conversion between
>integral types warning under MSC6.00?
>
>void strmem(char *mem, char *str, int n)
>{
>  if (str && mem)
>    while (n--)
>      *mem++=(*str)?(*str++):ACTUAL_SPACE;
>}
>
>where ACTUAL_SPACE is defined:
>
>#define ACTUAL_SPACE ' '
>

And the winner is....

that person who told me to cast the ' ' to a char.  K&R indicates that all
character constants are int's.  Who ever said to make (*str) into
(*str == 0): didn't help.  (also changes the sense of the expression).

Thanks for all of the responses.


Neil


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Neil I.  Weisenfeld                    | InterNet: weisen@eniac.seas.upenn.edu
Dept. of Computer and Info. Sciences   | USPS: I dunno, I'm moving...
University of Pennsylvania             | PENNmail: Don't even try it...
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