invalid lvalue in assignment

[mdh]

May I ask why this works:

given:
char s[];
char *posbfr = s;
char *endbfr = s + MAXOP;

void(...){
if (posbfr >= endbfr)
printf("......");
else
*posbfr++ = c ;
}


but this is invalid?

(posbfr >= endbfr) ? printf("......") : *posbfr++ = c ;

(with an "invalid lvalue in assignment") error?

or...is this the dumbest question yet?

Thank you.

 

[Ian Collins]

May I ask why this works:

given:
char s[];
char *posbfr = s;
char *endbfr = s + MAXOP;

void(...){
if (posbfr >= endbfr)
printf("......");
else
*posbfr++ = c ;
}


but this is invalid?

(posbfr >= endbfr) ? printf("......") : *posbfr++ = c ;

You are assigning c to the result of the conditional expression, so the
above equivalent to

((posbfr >= endbfr) ? printf("......") : *posbfr++) = c ;

 

[Peter Pichler]

May I ask why this works:

but this is invalid?

(posbfr >= endbfr) ? printf("......") : *posbfr++ = c ;

(with an "invalid lvalue in assignment") error?

Assignment is lower priority than ?:. The compiler sees your expression
as (cond ? x : y) = c;

Try explicit parentheses, like this:

(posbfr >= endbfr) ? printf("......") : (*posbfr++ = c) ;

 

[mdh]

Ian Collins wrote:

You are assigning c to the result of the conditional expression, so the
above equivalent to

((posbfr >= endbfr) ? printf("......") : *posbfr++) = c ;

Ian,
I know I am not then understanding this. I thought, given

expr1 ? expr2 : expr3;

then, if expr1 evaluates to true, then expr2 is evaluated, else if
false, expr3.

So, in the above case, is an assignment not regarded as a valid
expression?
..

 

[mdh]

Try explicit parentheses, like this:

(posbfr >= endbfr) ? printf("......") : (*posbfr++ = c) ;

Aha...thank you.