比较变量 PHP
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Compare variables PHP
提问by Harigntka
How can I compare two variable strings, would it be like so:
如何比较两个变量字符串，会是这样吗：
$myVar = "hello";
if ($myVar == "hello") {
//do code
}
And to check to see if a $_GET[] variable is present in the url would it be like this"
并检查 url 中是否存在 $_GET[] 变量，它会像这样"
$myVars = $_GET['param'];
if ($myVars == NULL) {
//do code
}
回答by John
$myVar = "hello";
if ($myVar == "hello") {
//do code
}
$myVar = $_GET['param'];
if (isset($myVar)) {
//IF THE VARIABLE IS SET do code
}
if (!isset($myVar)) {
//IF THE VARIABLE IS NOT SET do code
}
For your reference, something that stomped me for days when first starting PHP:
供您参考，当我第一次启动 PHP 时，这件事让我苦恼了好几天：
$_GET["var1"] // these are set from the header location so www.site.com/?var1=something
$_POST["var1"] //these are sent by forms from other pages to the php page
回答by Katsuke
For comparing strings I'd recommend using the triple equals operator over double equals.
为了比较字符串，我建议使用三等号运算符而不是双等号。
// This evaluates to true (this can be a surprise if you really want 0)
if ("0" == false) {
// do stuff
}
// While this evaluates to false
if ("0" === false) {
// do stuff
}
For checking the $_GET variable I rather use array_key_exists, isset can return false if the key exists but the content is null
为了检查 $_GET 变量，我宁愿使用 array_key_exists，如果键存在但内容为空，则 isset 可以返回 false
something like:
就像是：
$_GET['param'] = null;
// This evaluates to false
if (isset($_GET['param'])) {
// do stuff
}
// While this evaluates to true
if (array_key_exits('param', $_GET)) {
// do stuff
}
When possible avoid doing assignments such as:
在可能的情况下，避免执行以下任务：
$myVar = $_GET['param'];
$_GET, is user dependant. So the expected key could be available or not. If the key is not available when you access it, a run-time notice will be triggered. This could fill your error log if notices are enabled, or spam your users in the worst case. Just do a simple array_key_exists to check $_GET before referencing the key on it.
$_GET，取决于用户。所以预期的密钥可能可用或不可用。如果访问时密钥不可用，则会触发运行时通知。如果启用通知，这可能会填满您的错误日志，或者在最坏的情况下向您的用户发送垃圾邮件。在引用它的键之前，只需做一个简单的 array_key_exists 来检查 $_GET 。
if (array_key_exists('subject', $_GET) === true) {
$subject = $_GET['subject'];
} else {
// now you can report that the variable was not found
echo 'Please select a subject!';
// or simply set a default for it
$subject = 'unknown';
}
Sources:
资料来源：
http://ca.php.net/array_key_exists
http://ca.php.net/array_key_exists
回答by Niklas
If you wanna check if a variable is set, use isset()
如果您想检查是否设置了变量，请使用 isset()
if (isset($_GET['param'])){
// your code
}
回答by Niklas
To compare a variable to a string, use this:
要将变量与字符串进行比较，请使用以下命令：
if ($myVar == 'hello') {
// do stuff
}
To see if a variable is set, use isset(), like this:
要查看是否设置了变量，请使用 isset()，如下所示：
if (isset($_GET['param'])) {
// do stuff
}
回答by RobertPitt
All this information is listed on PHP's website under Operators
所有这些信息都列在 PHP 网站的 Operators 下
