In a project encountered a strange problem, it cost me a lot of time is not resolved, the final debugging found is the question of judgment-about 0 and "(empty single quotation marks, for good see I added a space), I found 0==" incredibly set up, depressed at the same time decided to write a simple page test, vowed to 0,null , empty, NULL, false the relationship is clear. Because this is likely to be a bug in some key places where we write programs that have Web sites. In particular, may affect the landing and other special places of security and logic correctness, although this is a very basic knowledge point, but many people, including some experts may be 0,null,empty, empty, false relationship is very vague. So it is still very necessary to do a test by yourself.
PHP Program code:
Copy CodeThe code is as follows:
//========= determines the relationship between 0 and ' and empty null false start =========//
if (' safdasefasefasf ' ==0) {
echo "The string is converted to a number equal to 0
";
}//output: The string is converted to a number equal to zero.
This is one of the key examples
This is explained in the manual: This value is determined by the first part of the string. If the string starts with a valid numeric data, the number is used as its value, otherwise its value is 0 (0).
Which means ' 3asfdf ' ==3; ' Adsfasdf ' ==0 quite to notice
$a = 0;
if ($a = = ") {
echo "0 equals"
";
}//output:0 Equals ' '
if (trim ($a) = = ") {
echo "Trim (0) equals"
";
}//no Output
if ($a = = =) {
echo "0==="
";
}//no Output
if (empty ($a)) {
echo "is empty
";
}//output: ' Is empty
if (Is_null ($a)) {
echo "0 is null
";
}//no Output
if (Is_numeric ($a)) {
echo "0 is numeric
";
}//output:0 is numeric
if (is_string ($a)) {
echo "0 is string
";
}//no Output
if (strval ($a) = = ") {
echo "0 is" converted into a string
";
}//no Output
========= determines the relationship of 0 and ' and empty null false end =========//
========= judgment ' and 0 and empty null false relationship start =========//
$b = ";
if ($b ==0) {
echo "'" Equals 0
";
}//output: ' Equals 0
if (! ') {
echo "' is false.
";
}//output: "is false
if (!0) {
echo "0 is false.
";
}//output:0 is False
========= judgment ' and 0 and empty null false relationship end =========//
echo "In judging the Empty (") must be careful, 0 is equivalent to ", 0 and" are equivalent to null characters and false, the best to judge the empty = = = ";
?>
The result of the output is: 0 equals "" is the empty 0 is numeric "equals 0" or false 0 is false in judging the empty (") must be careful, 0 is equivalent to", 0 and "are equivalent to null characters and false, the best to determine the empty = = = Only this explanation: 0 is also equivalent to ", 0 and" are equivalent to null characters and False
When judging the empty (") must be careful, 0 is equivalent to", 0 and "are equivalent to null characters and false, the best to judge the empty = = =;
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