php中0,null,empty,空,false,字符串关系的详细介绍
简介
php中0,null,empty,空,false,字符串关系的详细介绍
// 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 == '';";//输出
} else {
echo "0 != '';";
}
if (trim($a) == '') {
echo "trim(0) == '';";
} else {
echo "trim(0) != '';"; //输出,因为trim(0)为字符串'0'
}
if (strval($a) == '') {
echo "strval(0) == '';";
} else {
echo "strval(0) != '';"; //输出 strval — 获取变量的字符串值
}
//0=='',trim(0)!='',strval(0)!='' 不是空字符串
if ($a === '') {
echo "0 === '';";
} else {
echo "0 !=== '';"; //输出 还比较类型
}
//0!===''
if (empty($a)) {
echo "0 is empty;"; //输出
} else {
echo "0 is not empty;";
}
//0 is empty
if (is_null($a)) {
echo "0 is null;";
} else {
echo "0 is not null;"; //输出
}
//0 is not null
if (is_numeric($a)) {
echo "0 is numeric;"; //输出 如果$a='0',则结果相反
} else {
echo "0 is not numeric;";
}
//0 is numeric
if (is_string($a)) {
echo "0 is string;";
} else {
echo "0 is not string;"; //输出
}
//0 is not string
if (!$a) {
echo "0 is false;"; //输出
} else {
echo "0 is not false;";
}
//0 is 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;"; //输出
} else {
echo "'' != 0;";
}
if (intval($a) == 0) {
echo "intval('') == 0;"; //输出
} else {
echo "intval('') != 0;";
}
if (empty($a)) {
echo "'' is empty;"; //输出
} else {
echo "'' is not empty;";
}
if (is_null($a)) {
echo "'' is null;";
} else {
echo "'' is not null;";//输出
}
if (is_numeric($a)) {
echo "'' is numeric;";
} else {
echo "'' is not numeric;"; //输出
}
if (is_string($a)) {
echo "'' is string;"; //输出
} else {
echo "'' is not string;";
}
if (!$a) {
echo "'' is false;"; //输出
} 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 == '';"; //输出
} else {
echo "null != '';";
}
if ($a == 0) {
echo "null == 0;"; //输出
} else {
echo "null != 0;";
}
if ($a === '') {
echo "null === '';";
} else {
echo "null !=== '';"; //输出
}
if ($a === 0) {
echo "null === 0;";
} else {
echo "null !=== 0;"; //输出
}
if (strval($a) == '') {
echo "strval(null) == '';"; //输出
} else {
echo "strval(null) != '';";
}
if (intval($a) == 0) {
echo "intval(null) == 0;"; //输出
} else {
echo "intval(null) != 0;";
}
if (empty($a)) {
echo "null is empty;"; //输出
} else {
echo "null is not empty;";
}
if (is_numeric($a)) {
echo "null is numeric;";
} else {
echo "null is not numeric;"; //输出
}
if (is_string($a)) {
echo "null is string;";
} else {
echo "null is not string;"; //输出
}
if (!$a) {
echo "null is false;";
} else {
echo "null is not false;"; //输出
}