PHP如何检查变量是否为空_PHP中判断变量是否为空的常用方法

empty()

empty()

isset()

is_null()

empty()

0

"0"

""

null

false

array()

0

$var1 = "";
$var2 = 0;
$var3 = null;
$var4 = false;
$var5 = array();
$var6 = "hello";

if (empty($var1)) {
  echo "var1 is empty\n"; // 输出
}
if (empty($var2)) {
  echo "var2 is empty\n"; // 输出
}
if (empty($var3)) {
  echo "var3 is empty\n"; // 输出
}
if (empty($var4)) {
  echo "var4 is empty\n"; // 输出
}
if (empty($var5)) {
  echo "var5 is empty\n"; // 输出
}
if (empty($var6)) {
  echo "var6 is empty\n";
} else {
    echo "var6 is NOT empty\n"; // 输出
}

isset()

null

""

isset()

true

$var = "";
if (isset($var)) {
  echo "var is set\n"; // 输出
} else {
  echo "var is not set\n";
}

$var = null;
if (isset($var)) {
  echo "var is set\n";
} else {
  echo "var is not set\n"; // 输出
}

empty()

0

""

isset()

null

0

isset()

0

empty()

is_null()

null

null

true

$var1 = null;
$var2 = "";

if (is_null($var1)) {
  echo "var1 is null\n"; // 输出
}

if (is_null($var2)) {
  echo "var2 is null\n";
} else {
    echo "var2 is NOT null\n"; // 输出
}

is_null()

null

null

is_null()

Notice

isset()

if (isset($my_variable)) {
  // 使用 $my_variable
  echo $my_variable;
} else {
  // 处理变量未定义的情况
  echo "Variable is not defined";
}

$my_variable = ""; // 或者 null，或者其他合适的默认值
// 然后就可以安全地使用 $my_variable 了

@

$var = "";
if ($var === "") {
  echo "var is an empty string\n"; // 输出
}

$var = 0;
if ($var === 0) {
  echo "var is zero\n"; // 输出
}

trim()

$var = "   "; // 包含空格的字符串
if (empty(trim($var))) {
  echo "var is empty after trimming\n"; // 输出
}