[Resolved] Strange behavior from str_replace()

[kurtjensen]

I was trying to make a simple encryption routine when I found this strange behavior from str_replace(). It appears as though the function passes over the original string more than one time.

Is this normal?

Anyone know of a shortcut other than creating my own loops and recreating the str_replace() function?

<?php
function MyEncrypt($TextIn){
$OldArray = array("d","c","b","a");
$NewArray = array("a","b","c","d");

$TextOut = str_replace($OldArray, $NewArray, $TextIn);

return($TextOut);
}

function MyDecrypt($TextIn){
$OldArray = array("d","c","b","a");
$NewArray = array("a","b","c","d");

$TextOut = str_replace($NewArray, $OldArray, $TextIn);

return($TextOut);
}

$TextIn = "aaa bbb ccc ddd abcd";
$NewText = MyEncrypt($TextIn);
$OldText = MyDecrypt($NewText);

echo $TextIn."\n";
echo $NewText."\n";
echo $OldText."\n";

/
Outputs:
aaa bbb ccc ddd abcd
ddd ccc ccc ddd dccd
aaa bbb bbb aaa abba
/

/
I expected:
aaa bbb ccc ddd abcd
ddd ccc bbb aaa dcba
aaa bbb ccc ddd abcd
/
?>

[laserlight]

It appears as though the function passes over the original string more than one time.

It probably does since you're using arrays with it.
As such characters that have already been replaced are then treated as part of the string to search over, and so are replaced again.

In this case [man]strtr/man is more appropriate:

function MyEncrypt($TextIn) {
	return strtr($TextIn, "dcba", "abcd");
}

function MyDecrypt($TextIn) {
	return strtr($TextIn, "abcd", "dcba");
}

[kurtjensen]

Thanks laserlight,😃

That did what I need.

I still don't understand why
"It probably does since you're using arrays with it. "

The manual allows the use of arrays so why does it act different?
😕

[Weedpacket]

Because

$text = str_replace(array('a','b','c','d'), array('d','c','b','a'), $text);

Is the same as

$text = str_replace('a','d', $text);
$text = str_replace('b','c', $text);
$text = str_replace('c','b', $text);
$text = str_replace('d','a', $text);

Going through that you can see that first all the 'a's are replaced by 'd's, then all the 'b's are replaced by 'c's. Then all the 'c's are replaced by 'b's (including the ones that were 'b's to begin with) and then all the 'd's are replaced by 'a's (including the ones that were 'a's to begin with).

[kurtjensen]

I think it's all beginning to make a little sense now.

Could someone get me another strong cup of coffee?:o

Thanks again all🙂