Examples of file handles: locating the starting position of unseen reads and chunked reads of large files through handles

Examples of file handles: locating the starting position of unseen reads through handles and chunked reading of large files

In order to use the read file function , you need to use a path relative to the PHP script to point them to the file to read. However, most PHP file functions use a slightly different mechanism to access files. This mechanism is very similar to the mechanism of connecting to a database. The process Use the fopen() function to "connect" and the fclose function to "disconnect". The return value of the fopen function is a PHP file pointer, also known as a file handle. Once you have a file handle, you can use it to perform a variety of operations on the file, including deletion, append operations, etc. Then this handle is in use during use What issues need to be paid attention to?

Let’s first take a look at how files are opened and closed. The code is as follows:

<?php
$f_fopen = fopen("../file.txt.","rb");    //打开文件
  ....                               //对文件进行操作
fclose($f_fopen);                    //操作完成后关闭文件
?>

When using fopen to connect files, you must specify the file path and file access mode (for example: r means only read mode). b mode means that the file will be opened in binary mode, which can be used to ensure code portability between different operations.

1. Locate the starting position of file reading through the handle

Already have it when opening a file through the fopen() function A file handle. The following uses this handle to read the file. The code is as follows:

<?php
header("Content-Type:text/html; charset=utf-8");
$filename = "05.txt";                          //要读取的文件
$fp = fopen($filename,"rb");                   //打开文件
echo fread($fp,32);                            //使用fread()函数读取文件内容的前32个字节
echo "<p>";
echo fread($fp,filesize($filename));          //输出其余的文件内容
?>

The result is as follows:

This example demonstrates how to use the file handle. Note that when using fread, the second parameter is one byte in units, indicating the amount of data to be read from the file. When the file content is read to the set amount of data, the handle will be located at this location. If you want To continue reading other contents in this file, you can read the total size of the file through the filesize function, and use this value as the second parameter of fread. At this time, the output will be the remaining contents of the file. This is the role of the handle. .

2. Block reading of large files

The previous solution is very effective for reading small files, but it is not suitable for reading large files. When the contents of the file are retrieved, the server's memory will be occupied, which may cause performance issues at times. In order to reduce the possibility of this problem, you can use the method of reading files in blocks and operating with blocks as objects, thus avoiding memory usage. The principle is to open the file through the fopen function and use the while statement to read in a loop Get the contents of the file and stop the loop when the file pointer reaches the end of the file. Otherwise, use the fgets function to read the data in the file and move the entire file handle forward. The specific code for reading the file in blocks is as follows:

<?php
header("Content-Type:text/html; charset=utf-8");
$fopen = fopen("fun.php","rb");         
while(!feof($fopen)){             //使用 feof()函数测试指针是否到了文件结束的位置
    echo fgets($fopen);            // 输出当前行
}
fclose($fopen);
?>

There are also many functions that can read files using file handles. One of them is the fgetss function (note the two s), which is almost the same as fgets except that it can strip all HTML tag files it finds like the strip_tags function. The other is the fscanf function, which formats the output from a file like printf. There is also fgetcsv, which makes processing csv (comma separated values) files very easy.

But if you want to read the entire contents of a file into a variable, the file and file_get_content functions are easier to use, and they also potentially provide better performance.

So this is where we introduce how to use file handles. Friends should be able to master it easily!

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