&& 和 and 在 PHP 中邏輯功能相同，但優(yōu)先級不同，導致執(zhí)行順序不同；&& 優(yōu)先級高于 and，and 優(yōu)先級低于賦值操作符 =；因此 $success = true and false 實際被解析為 ($success = true) and false，使 $success 仍為 true；1. 在條件判斷中應使用 && 和 ||；2. 僅在控制流（如 $file = fopen() or die()）中使用 and 和 or；3. 復雜表達式應使用括號明確優(yōu)先級；4. 避免在賦值中混用 and/or 除非明確意圖如此；總之，盡管兩者邏輯等價，但因優(yōu)先級差異必須區(qū)分使用場景，以防止邏輯錯誤。

When writing PHP code, you might have seen both && and and used for logical operations — sometimes interchangeably, sometimes not. At first glance, they seem to do the same thing: evaluate whether two conditions are true. But there’s a subtle yet critical difference between && and and in PHP that can lead to unexpected bugs if misunderstood. Let’s break it down.

They’re Not Equal — Operator Precedence Matters

The key difference between && and and lies in operator precedence — that is, the order in which operators are evaluated in an expression.

• && has a higher precedence than and.
• In fact, and has very low precedence, lower than assignment (=), which can drastically change how your code behaves.

Let’s see this in action:

$success = true && false;
var_dump($success); // bool(false)

This works as expected. But now try using and:

$success = true and false;
var_dump($success); // bool(true) — Wait, what?!

Why is it true?

Because of how PHP parses the expression due to precedence:

// This is actually interpreted as:
($success = true) and false;

So $success gets assigned true, and then the and false part is evaluated but doesn’t affect the variable. The full expression evaluates to false, but the assignment already happened.

This is a common trap.

Practical Example: Chaining Operations

This issue often surfaces when combining assignment and logic:

$result = getData() or die('No data');

This pattern is actually safe because or (like and) has low precedence. It's interpreted as:

($result = getData()) or die('No data');

So if getData() returns false, the assignment still happens, and then die() is triggered.

But if you used || instead:

$result = getData() || die('No data');

That would be parsed as:

$result = (getData() || die('No data'));

Which means die() only runs if getData() is false, but the result of the entire expression (true/false) is assigned to $result, not the actual data. So you lose your data!

So When Should You Use Which?

Here’s a practical guide:

• ? Use && and || for logical conditions inside if, while, etc.

  if ($userValid && $inputValid) { ... }

• ? Use and and or only when you want low precedence for control flow (e.g., error handling).

  $file = fopen('data.txt', 'r') or die('Cannot open file');

• ? Avoid mixing and/or with assignment unless you explicitly understand and intend the behavior.

Quick Reference: Precedence Levels (High to Low)

So in expressions involving multiple operators, && binds tighter than and, and both and and or are weaker than assignment.

Best Practices

To avoid confusion:

• Stick with && and || in most conditional logic.
• Use parentheses when in doubt:

  if (($active == true) and ($admin == true)) { ... }

• Avoid relying on and/or unless you're using them for control flow patterns (like the die() example).
• Be extra cautious in complex expressions.

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Basically, && and and do the same logical operation — but when they happen in an expression is completely different. That tiny difference in precedence can lead to major logic bugs.

So while they may look interchangeable, treat them as distinct tools for different jobs.

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