在PHP中，邏輯運算符用于組合或評估條件，主要的運算符包括&&、and、||、or、!和xor。1.&&與and的區(qū)別在于優(yōu)先級，&&優(yōu)先級高于賦值運算符，而and則低于賦值運算符，因此在結(jié)合賦值時行為不同；2.||和or也有類似的優(yōu)先級差異，||優(yōu)先于賦值，而or在賦值之后處理；3.!運算符用于取反布爾值，常用于檢查條件是否為假，并建議用括號包裹復(fù)雜表達式以確保正確應(yīng)用；4.xor僅當(dāng)兩個值中恰好有一個為true時返回true，適用于互斥條件判斷；5.最佳實踐是優(yōu)先使用&&和||以獲得更可預(yù)測的行為，適當(dāng)使用括號提升可讀性，避免混合過多未分組的運算符，并謹(jǐn)慎使用xor以免造成誤解。

In PHP, logical operators are used to combine or evaluate conditions — especially in control structures like if, else if, and loops. The main ones you’ll use are && (and), || (or), ! (not), and their lowercase counterparts and, or, and xor. While they work similarly, there's one key difference: operator precedence. That affects how expressions are grouped and evaluated.

Here’s a practical breakdown of how to use them effectively.

Understanding && vs and

Both && and and check whether two conditions are true. The only difference is precedence.

• && has higher precedence than assignment operators.
• and has lower precedence.

This matters when you're combining assignments with logic:

$a = true && false;
var_dump($a); // false

$b = true and false;
var_dump($b); // true — because it evaluates as ($b = true) and then ignores the rest

So unless you’re intentionally relying on that behavior, stick with && for consistency and clarity.

How to Use || and or

Like && and and, || and or do similar things but have different precedence levels.

• || is evaluated before assignments.
• or is evaluated after assignments.

Example:

$c = false || true;
var_dump($c); // true

$d = false or true;
var_dump($d); // false — again, because it does $d = false first

In most cases, you'll want || because it behaves more predictably in conditionals.

When to Use ! (NOT)

The ! operator simply flips a boolean value.

Use it to check if something is not true:

if (!$isLoggedIn) {
    echo 'Please log in.';
}

It's commonly used with functions that return boolean values:

if (!file_exists('data.txt')) {
    echo 'File missing!';
}

Make sure to wrap complex expressions in parentheses when using ! so it applies correctly:

if (!(is_numeric($input) && $input > 0)) {
    echo 'Input must be a positive number.';
}

Using xor (Exclusive OR)

This one’s less common, but handy in specific cases.

xor returns true only when exactly one of the two values is true, not both.

Examples:

var_dump(true xor true);   // false
var_dump(true xor false);  // true
var_dump(false xor true);  // true
var_dump(false xor false); // false

You might use it in forms where the user should select one option from two, but not both. Or in state checks where mutual exclusivity matters.

Final Tips

• Prefer && and || over and, or unless you specifically need low-precedence behavior.
• Use parentheses liberally to avoid confusion.
• Avoid mixing too many operators without grouping — readability wins.
• Use xor sparingly; it's easy to misinterpret in complex logic trees.

基本上就這些。

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