5

I did a few tests with strings using '=='. I know to compare strings using '==' is not the way, but there is a weird behavior I want to solve.

I'm following the PHP documentation on page Comparison Operators. This is the test I did:

<?php
   var_dump( "100" == "1e2" ); // Outputs boolean true
   var_dump( (int) "100" ); // int 100
   var_dump( (int) "1e2" ); // int 1
?>

The documentation says when we compare strings with numbers, PHP first converts the string to numbers, but when I convert '100' and '1e2' to numbers they are not equal. The comparison should outputs boolean false.

Why is this weird behavior?

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2
  • Incidentally this is why it's usually best to use === instead of ==, since the result is far more predictable! Commented Jul 15, 2012 at 5:07
  • Re "compare strings using '==' is not the way": What is the way? Using three (===)? What is the canonical Stack Overflow question for it? Commented Jan 3, 2023 at 4:18

2 Answers 2

Reset to default
4

Not all numbers are integers. 1e2 is a float (that happens to be representable as an integer, but is not directly convertible to an integer). Try converting to floats rather than ints:

<?php 
   var_dump( "100" == "1e2" ); // bool(true)
   var_dump( (float) "100" );  // float(100)
   var_dump( (float) "1e2" );  // float(100)
?>
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1 Comment

To expand on this, here is the explanation in the docs. php.net/manual/en/… "If the string does not contain any of the characters '.', 'e', or 'E' and the numeric value fits into integer type limits (as defined by PHP_INT_MAX), the string will be evaluated as an integer. In all other cases it will be evaluated as a float."
0

Type Juggling is not equal to Type Casting

From the Type Juggling page

If either operand is a float, then both operands are evaluated as floats, and the result will be a float. Otherwise, the operands will be interpreted as integers, and the result will also be an integer.

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