使用 while() 生成随机文件名？

发布于 2024-12-04 08:29:27 字数 529 浏览 1 评论 0原文

我使用 while() 循环创建一个随机文件名，根据数据库检查它，然后如果它已经存在，则循环。我只是有点担心我的语法/用法不对，因为很久以前我只做过一次，并且从那时起就没有以这种方式使用过 while() 循环。

这是我的代码：

$i = 0;
while(++$i) {
    $file_name = md5(mt_rand(0,9999999)) . ".php";
    $result = mysql_query("SELECT * FROM x WHERE file_name = '{$file_name}'");

    if(mysql_num_rows($result) == 0) { break; } else { continue;}
}

这行得通吗？如果不行，有什么问题吗？

我知道这是一个小问题，但测试这是否有效似乎更加“任务繁重”（需要创建一个新表，更改文件名以从 1 - 3 个内容中进行选择，显示一条消息而不是继续等，任何帮助将不胜感激！

一如既往

原文

I'm using a while() loop to create a random file name, check it against a database, then if it already exists, loop. I'm just a little worried my syntax/usage is off, as I've only done this once before ages ago, and haven't used a while() loop in this way since then.

Here's my code:

$i = 0;
while(++$i) {
    $file_name = md5(mt_rand(0,9999999)) . ".php";
    $result = mysql_query("SELECT * FROM x WHERE file_name = '{$file_name}'");

    if(mysql_num_rows($result) == 0) { break; } else { continue;}
}

Would this work, and if not, what's wrong with it?

I know it's a petty question, but testing out whether or not this would work seems a lot more "tasky" (need to create a new table, alter the file name to choose from 1 - 3 things, display a message instead of continue etc.

Any help, as always, would be appreciated!

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网白 2024-12-11 08:29:27

你不需要 $i，因为你没有使用它，并且你不需要在循环中 continue - 循环会自动循环，这就是什么确实如此。当您达到想要结束循环的条件时，您只需要break：

while(true) {
    $file_name = md5(mt_rand(0,9999999)) . ".php";
    $result = mysql_query("SELECT * FROM x WHERE file_name = '{$file_name}'");

    if (mysql_num_rows($result) == 0) break;
}

不过，您使用散列的方式略有破坏。您应该生成一个比 MD5 哈希值更长的随机字符串，而不是更短。现在，您只有 10,000,000 个可能的文件名 (0..99999999)，而不是 MD5 可以生成的完整 2^128 个文件名。不必担心 2^128 这样大的空间中的哈希冲突，您更有可能简单地生成相同的数字两次，从而导致多次访问数据库。

You don't need $i, since you're not using it, and you don't need to continue in a loop - the loop will automatically loop, that's what it does. You only need to break when you reach the condition under which you want to end the loop:

while(true) {
    $file_name = md5(mt_rand(0,9999999)) . ".php";
    $result = mysql_query("SELECT * FROM x WHERE file_name = '{$file_name}'");

    if (mysql_num_rows($result) == 0) break;
}

You're using hashes in a slightly broken way though. You should be generating a random string longer than an MD5 hash, not shorter. Right now you only have 10,000,000 possible filenames (0..99999999) instead of the full 2^128 that a MD5 can produce. Instead of worrying about hash collisions in a space as large a 2^128, you have a much higher chance of simply generating the same numbers twice, causing multiple trips to the database.

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