Detailed introduction to the relationship between 0, null, empty, empty, false, and strings in PHP_PHP Tutorial

//========== Determine 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 to 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 starts with legal numeric data, and uses that number as its value, otherwise its value is 0 (zero)
That is to say '3asfdf'==3; 'adsfasdf'==0 is quite necessary. Note that
$a=0;
if($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 relationship 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
//=== ====== Determine the relationship between '' and 0 and empty null false end =========//
echo "Be careful when judging empty (''), 0 is also equivalent For '', 0 and '' are equivalent to the empty character and false. It is best to use ===";
?>