Comparing String to Integer gives strange results

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I'm really confused as to why this operation works. Can someone explain it?

$test1 = "d85d1d81b25614a3504a3d5601a9cb2e";
$test2 = "3581169b064f71be1630b321d3ca318f";

if ($test1 == 0)
  echo "Test 1 is Equal!?";
if ($test2 == 0)
  echo "Test 2 is Equal!?";

// Returns: Test 1 is Equal!?

For clarification, I am trying to compare the string "0" to the $test variables. I already know to fix the code I can just enclose (as I should have) the 0 in ""s

I'm wondering if this is a PHP bug, a server bug, or somehow a valid operation. According to http://us3.php.net/types.comparisons this should not have worked.

Edit: Scratch that, apparently it does mention that Loose comparisons between string and 0 is true. But I still don't know why.

Edit 2: I've revised my question, why does the $test2 value of "3581169b064f71be1630b321d3ca318f" not work?

Answers

From the PHP manual:

String conversion to numbers

When a string is evaluated in a numeric context, the resulting value and type are determined as follows.

The string will be evaluated as a float if it contains any of the characters '.', 'e', or 'E'. Otherwise, it will be evaluated as an integer.

The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.

Thursday, August 11, 2022

nhunston-8786a945d7dc

Use bindec() function to convert from binary to decimal:

$value = bindec("10101011010101");

Sunday, October 9, 2022

bjoern

Do not drop the column, it will clear the data.

You can however try

change_column :people, :company_id, :integer

and if all values in company_id can be converted to integer, it should be fine.

If that is not the case (ie not all string can be converted by default), then you can do it in two steps: 1) create a new column, then load the company_id in there after some conversion. 2) drop company_id then rename the new column.

You should be careful with both methods (more so for the second one) and you should probably do it first on a copy of the database, if you can.

Friday, December 9, 2022

matheus_lacerda

It's not a bug, it's a feature. Any string can be casted to an integer, but the cast will return 0 if the string doesn't start with an integer value. Also, when comparing an integer and a string, the string is casted to an integer and then the check is done against the two integers. Because of that rule, about just any random string is "equal" to zero. (To bypass this behavior, you should use strcmp, as it performs an explicit string comparison by casting anything passed to a string.)

To make sure I'm dealing with an integer, I would use is_numeric first, then convert the string to an int, and verify that the stringified int corresponds to the input value.

if (is_numeric($value) && strcmp((int)$value, $value) == 0)
{
    // $value is an integer value represented as a string
}

Tuesday, September 6, 2022

frankm

Ah, finally I got it. It was quite stupid of me.

Comparison involves not only "is equal" but also "less than" and "greater than". And for the latter two it is obviously critical to cast numerical operands before comparison, because numbers often being represented in PHP as strings, and 11 have to be greater than 9 even if both stored in strings.

So, as compare_function() does all the comparisons at once, returns either 1, 0, -1 to tell if first operand is bigger, equal or less than second respectively - well, it's fairly explains, why operands being cast.

Saturday, September 24, 2022

nigel_stackhouse

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Comparing String to Integer gives strange results

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