In-depth understanding of 0,null,empty, NULL, FALSE, and string relationships in PHP

Determine 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 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 "'" Equals 0 "; }//output: ' Equals 0 if (! ') { echo "' is false. "; }//output: "is false if (!0) { echo "0 is false. "; }//output:0 is False bbs.it-home.org 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 = = = "; ?> Copy Code Output: 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 Sample interpretation: 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 = = =; echo 0 = = NULL; Echo ' * * ' ; Trueecho 0 = = = NULL; Echo ' * * ' ; Falseecho (string) 0! = NULL; Echo ' * * ' ; Trueecho 0! = null; Echo ' * * ' ; Falseecho 0!== null; Echo ' * * ' ; True

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