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

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

// Judge the relationship between 0 and ''and empty null false. start // If ('safdasefasefasf' = 0 ){ Echo "this string is converted to a number equal to 0 "; } // Output: the string is converted to a value equal to zero. This is a key example. This value is determined by the first part of the string. If a string starts with a valid number, use this number as its value. Otherwise, its value is 0 (0 ). That is to say, '3asfdf '= 3; 'adsfasdf' = 0. $ 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 ($ )){ Echo "'' is empty "; } // Output: ''is empty If (is_null ($ )){ Echo "0 is null "; } // No output If (is_numeric ($ )){ Echo "0 is numeric "; } // Output: 0 is numeric If (is_string ($ )){ Echo "0 is string "; } // No output If (strval ($ a) = ''){ Echo "convert to string 0 is'' "; } // No output // Determine the relationship between 0 and ''and empty null false. end // // Judge 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 // Determine the relationship between ''and 0 and empty null false. end // Echo "when judging null (''), be careful. 0 is equivalent to '', 0 and'', both are equivalent to null and false, it is best to use = "; ?> Output result: 0 is equal to "" is empty 0 is numeric "is equal to 0". false 0 is false. be careful when determining null ("). 0 is equivalent ", both 0 and "are equivalent to null characters and false. it is best to use = to judge as null. it can only be interpreted as follows: 0 is also equivalent to", 0 and "are equivalent to null characters and false. Be careful when determining the null ("). 0 is equivalent to", 0 and "are equivalent to null characters and false. it is best to use = to judge the null; Echo 0 = null; echo '** '; // Trueecho 0 === null; echo '** '; // Falseecho (string) 0! = Null; echo '** '; // Trueecho 0! = Null; echo '** '; // Falseecho 0! = Null; echo '** '; // True