Comparison between a numeric string and an alphanumeric string

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13

The following operation returns true:

var_dump("1" == "1e0"); //1 == 1 -> true

But if I add an "e" at the end of the second string, it already returns false:

var_dump("1" == "1e0e"); //1 == 1 -> false???

If you do the following operation, returns 2:

echo (int)"1" + (int)"1e0e"; // 2

My question is, why the second operation returns false if in the third operation, I am converting the values to integer and returns 1 + 1, ie in the second operation the comparison should be 1 == 1, would not have to return true?

Another question is, if I am comparing 2 strings, why does the first operation return true if they are two different strings?

php string numerical-representation

3 answers

15


1e0 is the scientific notation for 1 i.e 1 vezes 10 elevado a 0. And the php converts numeric strings in numbers for comparison.

var_dump("1000" == "1e3"); //1000 == 1000 -> true 
var_dump("1" == "1e0"); //1 == 1 -> true

1e0e is not a valid notation therefore:

var_dump("1" == "1e0e"); //1 != da string "1e0e"

Whenever you do casting you will see that this occurs, as casting forces conversion into integer:

var_dump((int)"1" == (int)"1e0e"); // true
  • 4

    This is one of the many drawbacks of PHP. This "achism", this "intrusion" is a major cause of difficult to debug bugs.

  • So, why in the var_dump function the string "1e0" is converted to numeric but the "1e0e" is not? It should not convert to 1 as it does at first without the need of (int) before the string?

  • @Felipe because as already said in the reply 1e0e is not a notation valid scientific.

  • 1

    @Brunoaugusto I agree, if I’m comparing Apples to Oranges, it’s not because both are fruits that I want them to return true.

  • Blessed be the polymorphism provided by interfaces \the/

8

To avoid confusion at the time of comparison use === instead of ==, so beyond the content PHP will compare the type too.

var_dump("1" === "1e0"); // false

String "1" is different from string "1e0"

var_dump("1" === "1e0e"); // false

String "1" is different from string "1e0e"

var_dump((int)"1" == (int)"1e0e"); // true

Whole 1 is equal to the whole 1

3

Compare === does not solve, see that 0xFA is 250, so ( 250 === 0xFA ) results in TRUE

1) Compare the size of a string to an input that is: 0xFA

if( $string <= 255 ) // 250 < 255 // Logo retornará TRUE


2) Convert to string causes the same effect:

( (string)255 === (string)0xFF )

Your example:

Here you have a simple string comparison, 1e0e does not take integer value and 1 == 1 is not the operation that occurs.

var_dump("1" == "1e0e"); //1 == 1 -> false???


Here you have 1e0e as a string and when it converts INT, it naturally assumes the value of 1, which added with 1 results in 2;

echo (int)"1" + (int)"1e0e"; // 2

If you want to compare effectively, you will have to make a combination of checks:
. You can force input to assume a string value with (string)$input
. Combine mb_strlen to compare the length of entries.

If you can, more information on the type of check.

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