Php string and number comparison problems

Source: Internet
Author: User
Tags numeric

Today, I encountered a problem. According to the interface description, the numbers 0, 1, 2, and so on are returned. 0 indicates that the operation is successful, and other values indicate different error codes. The program uses if ($ ret = 0) to determine whether the program is good. Today, a problem occurs. Because the other party's interface is modified, a letter string is directly returned as an error message, then, my side is tragic. The above judgment will always be TRUE.

The reason is that php is a weak type language, so we can compare two different types of variables, but before the comparison, php will convert one party to the other, this is important. If it is a string and a number for comparison, php will forcibly convert the string to a number. For a string of pure letters, it is 0 after conversion, so if ($ ret = 0) yes.

PHP manual/language reference/operator/comparison operator can be found.

In PHP, when two numeric strings (strings containing only numbers) are compared, they are directly converted to numerical values for comparison.
Example: (note that the last two variables $ a and $ B are not equal)

 

The code is as follows: Copy code

// Example 1
<? Php
$ A = '000000 ';
$ B = '000000 ';
If ($ a = $ B ){
Echo 'equal ';
} Else {
Echo 'notequal ';
}
?>

Running the above program finds that the result is equal (not the result we think)

Add a letter a to $ a and $ B respectively.

The code is as follows: Copy code


// Example 2
<? Php
$ A = 'a0000203199106034578 ';
$ B = 'a0000203199106034579 ';
If ($ a = $ B ){
Echo 'equal ';
} Else {
Echo 'notequal ';
}
?>

The output is notEqual (correct result)

Example 1 is equal because PHP converts two numeric strings to a numeric string, and the two numbers are exactly the same.

The code is as follows: Copy code

<? Php
$ A = 511203199106034578;
$ B = 511203199106034579;
Echo $ a; // output 5.1120319910603E + 17, that is, 511203199106030000
Echo $ B; // output 5.1120319910603E + 17, that is, 511203199106030000
?>

So the result we get in Example 1 is equal.

To avoid this unexpected result, use the type comparison operator ===( if $ a is equal to $ B and their types are the same)

The code is as follows: Copy code

// Example 4
<? Php
$ A = '000000 ';
$ B = '000000 ';
If ($ a ===$ B ){
Echo 'equal ';
} Else {
Echo 'notequal ';
}
?>

In this way, we can get the expected notEqual.

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