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Posted by Hilarion on 11/24/90 11:29
>> I can understand the following :
>> $a = 10;
>> $b = $a++;
>> print("$a, $b");
>> will print 11, 10 on the screen.
>> because when $b = $a++ first thing that happens is $b = $a
>> and then $a = $a + 1. I am willing to and can accept that.
>
> I wouldn't try to understand the sublety of the post increment
> operator. It really has no reason to exist other than the fact that its
> syntax was modeled after that of C, a language that's much closer to
> machine code. You wouldn't really see the logic behind it unless you
> understand how a CPU works.
>
> Post-increment means you use the value of a variable, then increment
> it. This happens quite often in low-level programming. For example, to
> compare two strings, you'd want to tell the CPU to compare the byte at
> memory address A with the byte at memory address B, then increment A
> and B, so that they point to the following pair of characters for the
> next comparison. Instead sending three instructions--compare,
> increment, increment--to a CPU like x86 you send just one--the "scan
> string" instruction. This short-hand thus speed up the operation three
> times.
>
> In any event, the reason print($i++) yields 1 is because parentheses
> don't actually do anything. They are only used for resolving
> precedence. The post-increment occurs right after the variable is
> read--after the print operation in this case.
>
> Another example to consider is print ($i++ + $++). This'd be the
> sequence of events:
>
> 1. To perform the addition operation, A + B, PHP reads $i (which is 1)
> for A
> 2. PHP increment $i
> 3. PHP reads $i (which is now 2) for B
> 4. PHP increment $i again
> 5. PHP passes the result of A + B to print, which is 3
>
> So you see, post increment isn't the last thing that happens. It
> happens right after the variable is read.
Thanx for the clarification. I was wrong in my last post in that topic
and was unaware of it. I've read manuals for PHP (and earlier for C/C++)
describing it but for some cause I remembered it the wrong way and never
had to use it in a way you showed it (increment same variable twice
in same instruction), so I never hit the situation which would show me
I'm wrong. Thank you again.
Hilarion
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