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Typo produces unexpected results in PHP

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By User


Just found a piece of my code that had one original typo in it. 





$msg = "Some text";

$msg .= " some more text";

$msg .+ " yet more text!";

$msg .= " last text";


Notice the .+ that should be .= . What surprises me is that the code ran without producing any error, warning or notice and the output was:



Some text some more text last text



I was wondering why it did that. I know full well what .= and += are but how is .+ interpreted especially since there is no equal sign.


Source: Tips4all, CCNA FINAL EXAM
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Comments

  1. UserMay 11, 2012 at 4:41 AM

    There's no .+ operator, so that is . followed by +.

    You're building an expression that consists of $msg concatenated with the result of applying unary + to " yet more text!" (which is 0 due to the cast to integer) ... and then discarding the whole thing because you're not doing anything with the result.

    $msg .+ " yet more text!";
    $msg . +" yet more text!"; // 1. PHP doesn't care about the spacing
    $msg . 0; // 2. Conversion to int from unary `+`
    $msg . "0"; // 3. Coersion to string for concatenation
    // 4. Nothing done with value


    It's perfectly valid; it just doesn't do anything useful.

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  2. UserMay 11, 2012 at 4:41 AM

    The + gets interpreted as a unary plus. PHP casts the string into an integer with the value 0 and concatenates it with $msg. However you do not assign $msg anything on that line, so $msg won't be changed.

    ReplyDelete
  3. UserMay 11, 2012 at 4:42 AM

    This works because the . is the concatenation operator, and + is the addition operator.

    The line got interpreted like this:

    $msg . (+" yet more text!");


    The expression +" yet more text!" converts the string to an int (0 in this case as when PHP converts a string to an int, it stops at the 1st non-number character). It then concated the 0 to $msg, and ignored the result.

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