PHP中空字符串介绍0、null、empty和false之间的关系

2019-11-22 00:40:25

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如果用错方法函数或是用少了，如果几个方法函数的逻辑顺序错了，很可能就是一个漏洞，而且不容易找出来。纠结啊~

上网找找看哪位高人有总结出相关的结论出来，果然有！不过似乎不是很全面，我在这里稍完善了一下，仅供参考。

 
// 判断 0 与 ''、null、empty、false 之间的关系 
$a = 0; 
echo "0 与 ''、 empty、null、false 之间的关系："; 
if($a == ''){ 
echo "0 == '';"; 
}else{ 
echo "0 != '';"; 
} 
if(trim($a) == ''){ 
echo "trim(0) == '';"; 
}else{ 
echo "trim(0) != '';"; 
} 
if(strval($a) == ''){ 
echo "strval(0) == '';"; 
}else{ 
echo "strval(0) != '';"; 
} 
if($a === ''){ 
echo "0 === '';"; 
}else{ 
echo "0 !=== '';"; 
} 
if(empty($a)){ 
echo "0 is empty;"; 
}else{ 
echo "0 is not empty;"; 
} 
if(is_null($a)){ 
echo "0 is null;"; 
}else{ 
echo "0 is not null;"; 
} 
if(is_numeric($a)){ 
echo "0 is numeric;"; 
}else{ 
echo "0 is not numeric;"; 
} 
if(is_string($a)){ 
echo "0 is string;"; 
}else{ 
echo "0 is not string;"; 
} 
if(!$a){ 
echo "0 is false;"; 
}else{ 
echo "0 is not false;"; 
} 
// 判断 '' 和 0、null、empty、false 之间的关系 
$a = ''; 
echo "'' 和 0、empty、null、false 之间的关系："; 
if($a == 0){ 
echo "'' == 0;"; 
}else{ 
echo "'' != 0;"; 
} 
if(intval($a) == 0){ 
echo "intval('') == 0;"; 
}else{ 
echo "intval('') != 0;"; 
} 
if(empty($a)){ 
echo "'' is empty;"; 
}else{ 
echo "'' is not empty;"; 
} 
if(is_null($a)){ 
echo "'' is null;"; 
}else{ 
echo "'' is not null;"; 
} 
if(is_numeric($a)){ 
echo "'' is numeric;"; 
}else{ 
echo "'' is not numeric;"; 
} 
if(is_string($a)){ 
echo "'' is string;"; 
}else{ 
echo "'' is not string;"; 
} 
if(!$a){ 
echo "'' is false;"; 
}else{ 
echo "'' is not false;"; 
} 
// 判断 null 和 ''、0、empty、false 之间的关系 
$a = null; 
echo "null 和 ''、0、empty、false 之间的关系："; 
if($a == ''){ 
echo "null == '';"; 
}else{ 
echo "null != '';"; 
} 
if($a == 0){ 
echo "null == 0;"; 
}else{ 
echo "null != 0;"; 
} 
if($a === ''){ 
echo "null === '';"; 
}else{ 
echo "null !=== '';"; 
} 
if($a === 0){ 
echo "null === 0;"; 
}else{ 
echo "null !=== 0;"; 
} 
if(strval($a) == ''){ 
echo "strval(null) == '';"; 
}else{ 
echo "strval(null) != '';"; 
} 
if(intval($a) == 0){ 
echo "intval(null) == 0;"; 
}else{ 
echo "intval(null) != 0;"; 
} 
if(empty($a)){ 
echo "null is empty;"; 
}else{ 
echo "null is not empty;"; 
} 
if(is_numeric($a)){ 
echo "null is numeric;"; 
}else{ 
echo "null is not numeric;"; 
} 
if(is_string($a)){ 
echo "null is string;"; 
}else{ 
echo "null is not string;"; 
} 
if(!$a){ 
echo "null is false;"; 
}else{ 
echo "null is not false;"; 
} 
echo ""; 