PHP does not read the first line of txt data

In PHP development, reading files is a very common operation. However, sometimes we encounter such a situation: although the file exists, when reading the file, we find that the first line of data has not been read. This kind of problem often makes developers feel very confused and distressed. This article will help developers fully understand this problem and solve it smoothly by analyzing the cause and solution of the problem.

1. Problem background

In PHP, there are many ways to read files. The more common ones are to use the file_get_contents() function and the fopen() function to read files. We usually store the information of the file to be read in an array so that the file information can be called at any time. The following is a common PHP code for reading files:

<?php
$file = 'test.txt';
$content = file_get_contents($file);
$lines = explode("\n", $content);
?>

In the above code, we first define a $file variable to store the file name to be read, and then use the file_get_contents() function to read the file And store the file content in the $content variable, and then use the explode() function to split the string in the $content variable using the "\n" delimiter as a condition to generate an array $lines to store each line of data in the file. .

However, when we read a file, we sometimes find some strange phenomena. For example, only the second line of the file and subsequent data are read, but the first line of data cannot be read successfully. Pick.

2. Problem Analysis

The usual reason for this problem is that when the operating system reads a text file, it will append a BOM (Byte Order Mark) mark to the beginning of the file by default. BOM The purpose of the flag is to tell the operating system which endian mode to use when reading the file. For some early operating systems or some software that is not suitable for UTF-8 encoding, it is difficult to process text files containing BOM tags. At this time, if we use file reading functions such as PHP's file_get_contents() function or fopen() function to read these files with BOM tags, the first line of data will not be read.

3. Solution

To address this problem, we can adopt the following solutions:

1. Delete BOM mark

We can use an editor or some text processing tools to open the text file to be read, then delete the BOM mark in the file header, then save the file and upload it to the server. This will ensure that the PHP file will no longer be affected by the BOM mark when reading it.

2. Use a special reading method

If we determine that the file to be read must have a BOM tag, we can use a special reading method to read the test document. Specifically, we can use some third-party PHP libraries, such as the fread() function to read the text file, and then use the substr() function to delete the first character (i.e. BOM mark) in the read string. , and finally process the string into an array. The following is a piece of PHP code that processes BOM tags:

<?php
$file = fopen("test.txt", "r");
$fcontents = fread($file, filesize("test.txt"));
fclose($file);

if(substr($fcontents, 0, 3) == pack("CCC",0xef,0xbb,0xbf)) {
  $fcontents = substr($fcontents, 3);
}

$lines = explode("\n", $fcontents);
?>

In the above code, we use the fopen() function to open the file to be read, and then use the fread() function to read the contents of the entire file. Next, we use the substr() function to check whether the file header has a BOM tag. If so, use the substr() function to delete the first character (i.e., the BOM tag) from $fcontents, and finally use the explode() function to The string is divided into an array $lines according to lines to complete the reading operation of the text file.

3. Convert the file encoding to UTF-8

If we cannot remove the BOM mark in either case, we can consider converting the encoding format of the source file to UTF-8 format, so that the impact of the BOM mark can be avoided when reading files. We can use Windows system's explicit symbol conversion or tools such as notepad to convert the file to UTF-8 encoding.

4. Summary

The above is a detailed analysis of the reasons and solutions for the problem that the first line of data cannot be read when PHP reads a file. Generally speaking, this kind of problem is not difficult to solve. We only need to understand the cause of the problem and adopt appropriate solutions to successfully avoid the impact of this problem on the program.

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