In-depth understanding of the relationship between 0, null, empty, empty, false, and strings in PHP

//Judge the relationship between 0 and '' and empty null false start//
if('safdasefasefasf'==0) {
 echo "The string is converted into a number equal to 0 ";
}//output: The string is converted into a number equal to zero.
 This is a key example
The manual explains: The value is determined by the first part of the string. If the string begins with legal numeric data, that number is used as its value, otherwise its value is 0 (zero).
In other words, '3asfdf'==3 ; 'adsfasdf'==0 Be very careful
$a=0;
if($a= =''){
 echo "0 is equal to '' ";
} //output:0 is equal to ''
if(trim($a)==''){
 echo "trim(0 ) is equal to '' ";
} //no output
if($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 converted into a string is '' ";
} //no output
// Determine the relationship between 0 and '' and empty null false end //
// Determine the relationship between '' and 0 and empty null false start //
$b = '';
if($b==0){
 echo "'' is equal to 0 ";
} //output:'' is equal to 0
if(!''){
 echo "'' is false ";
} // output:'' is false
if(!0){
 echo "0 is false ";
} //output:0 is false bbs.it-home.org
// Judge '' and The relationship between 0 and empty null falseend //
echo "Be careful when judging empty (''), 0 is also equivalent to '', 0 and '' are both equivalent to empty Characters and false, it is best to use ===";
?>

Output results: 0 is equal to " " is empty 0 is numeric " is equal to 0 " which is false. 0 is false. Be careful when judging empty ("). 0 is also equivalent to ". 0 and " are both equivalent to empty characters and false, and are judged to be empty. It is best to use === and can only be explained this way: 0 is also equivalent to ", 0 and " are equivalent to the null character and false. Be careful when judging empty ("). 0 is also equivalent to ", 0 and " are equivalent to empty characters and false. It is best to use === when judging empty;

echo 0 == null; echo '**
' ; //true echo 0 === null; echo '**
' ; //false echo (string)0 != null; echo '**
' ; //true echo 0 != null; echo '**
' ; //false echo 0 !== null; echo '**
' ; //true