Hallo, Daniel!

*** Am Donnerstag 25. Juli 1996 um 02:01 schrieb Daniel Lynes an Thomas Seeling:

 TS>> *x++;

This is evaluated as x++, plus its side-effect is the value of *x.

 DL> test.c(5): Warning! W302: Expression is only useful for its side effects

The compiler tells you this.

 TS>> /* this is illegal, since x does not contain a
"legal" pointer */
 TS>> z=*x;
It is illegal, *if* "int *x" is only a pointer to _one_ int, not to
an array of (at least 2) ints.

The pointer is incremented, but it does contain any legal pointer value.
So, consequently, accessing the value "behind" that pointer is illegal
as well.

 DL> However, the compiler does not spit out an error for this; nor, do I
The compiler cannot know that you just send one integer to the function.
"int *x" is either used to change the value of x, or to access a
whole array of ints.

 DL> pointer x, to the variable, z.  Why is this illegal?  Did you try
 DL> compiling it?
I am used to C for quite some years now. This is a typical beginner's
mistake, and I don't need to start the compiler to know where the fault is.

 DL> number, lending to the fact that *x++; is only useful for its side
 DL> effects. i.e.  its behaviour is unpredictable.
It is not wrong to use a statement "*x++", but it's useless. You
want to write (*x)++. Have a look at the operator precedences in a C
learning or reference book. You could either write "++*x".

This is not specific to OS/2, so you should continue discussing this in
C_ECHO, comp.lang.c or a similar local newsgroup.


Tschau...Thomas

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