fread
(PHP 4, PHP 5, PHP 7)
fread — 读取文件（可安全用于二进制文件）
说明
fread (
resource
$handle ,
int $length ) :
string
fread() 从文件指针 handle 读取最多 length 个字节。 该函数在遇上以下几种情况时停止读取文件：
- 读取了
length个字节 - 到达了文件末尾（EOF）
- a packet becomes available or the socket timeout occurs (for network streams)
- if the stream is read buffered and it does not represent a plain file, at most one read of up to a number of bytes equal to the chunk size (usually 8192) is made; depending on the previously buffered data, the size of the returned data may be larger than the chunk size.
返回值
返回所读取的字符串， 或者在失败时返回 FALSE。
范例
Example #1 一个简单的 fread() 例子
<?php
// get contents of a file into a string
$filename = "/usr/local/something.txt";
$handle = fopen($filename, "r");
$contents = fread($handle, filesize($filename));
fclose($handle);
?>
Example #2 Binary fread() example
Warning
在区分二进制文件和文本文件的系统上（如 Windows）打开文件时，fopen() 函数的 mode 参数要加上 'b'。
<?php
$filename = "c:\\files\\somepic.gif";
$handle = fopen($filename, "rb");
$contents = fread($handle, filesize($filename));
fclose($handle);
?>
Example #3 Remote fread() examples
Warning
当从任何不是普通本地文件读取时，例如在读取从远程文件或 popen() 以及 fsockopen() 返回的流时，读取会在一个包可用之后停止。这意味着应该如下例所示将数据收集起来合并成大块。
<?php
// 对 PHP 5 及更高版本
$handle = fopen("http://www.example.com/", "rb");
$contents = stream_get_contents($handle);
fclose($handle);
?>
<?php
$handle = fopen("http://www.example.com/", "rb");
$contents = '';
while (!feof($handle)) {
$contents .= fread($handle, 8192);
}
fclose($handle);
?>
注释
Note:
如果只是想将一个文件的内容读入到一个字符串中，用 file_get_contents()，它的性能比上面的代码好得多。
Note:
Note that fread() reads from the current position of the file pointer. Use ftell() to find the current position of the pointer and rewind() to rewind the pointer position.
