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Home Backend Development PHP Tutorial 请教PHP fflush 的问题, not working

请教PHP fflush 的问题, not working

Jun 06, 2016 pm 08:21 PM
php

有没有用过 fflush 函数

官方解释是这样说的:
Flushes the output to a file
This function forces a write of all buffered output to the resource pointed to by the file handle.

也就是说把文件的写入缓存强行释放输出到文件指针.
http://php.net/manual/en/function.fflush.php

但我发现 fwrite 在执行完之后, 内容就马上写入文件了. 不需要fflush, 也不需要fclose, 对这个问题感到很疑惑, fflush 究竟有提供了什么作用.

代码:

<?php

$fp = fopen("fflush.txt", "w+");
for ($i = 0; $i < 10; $i++) {
    fwrite($fp, "Write something here\n"); // 马上写入内容, 根本不存在 buffer 一说啊!
    sleep(1);
}
fflush($fp);
fclose($fp);
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回复内容:

有没有用过 fflush 函数

官方解释是这样说的:
Flushes the output to a file
This function forces a write of all buffered output to the resource pointed to by the file handle.

也就是说把文件的写入缓存强行释放输出到文件指针.
http://php.net/manual/en/function.fflush.php

但我发现 fwrite 在执行完之后, 内容就马上写入文件了. 不需要fflush, 也不需要fclose, 对这个问题感到很疑惑, fflush 究竟有提供了什么作用.

代码:

<?php

$fp = fopen("fflush.txt", "w+");
for ($i = 0; $i < 10; $i++) {
    fwrite($fp, "Write something here\n"); // 马上写入内容, 根本不存在 buffer 一说啊!
    sleep(1);
}
fflush($fp);
fclose($fp);
Copy after login
Copy after login

给你参考一个方法 stream_set_write_buffer ,默认的 buffer_size8K ,也就是说,fwrite 如果一次写入的数据量大于 buffer_size ,会拆分写入。这种情况在多进程操作同一文件时需要考虑,通常情况下 fflush 是没多大作用的,不过加了也无所谓,毕竟 fopen 还能打开其他的 文件 似的资源。

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