What exactly is PHP bom? One article analysis

What exactly is PHP bom? Analysis of one article

In the field of programming, many programmers will encounter BOM problems when processing PHP files. So, what exactly is PHP bom? Let’s find out.

1. What is BOM

BOM, the full name is Byte Order Mark (byte order mark), is a special mark located at the beginning of a computer file, used to represent the encoding form and bytes of the file order. BOM is particularly common when dealing with Unicode-encoded files. It can help the parser clarify the encoding method of the file and avoid garbled characters. However, in PHP development, BOM sometimes causes some troubles.

2. The impact of BOM on PHP

In PHP files, if there is a BOM header, it will be regarded as additional output, resulting in an invisible blank in front of the output content. Characters can easily cause the problem of repeated output of headers. For example, when a PHP file contains a BOM header, if you try to output HTTP header information or perform redirection, etc., a "headers already sent" error will occur.

3. How to avoid BOM problems

1. Use editor settings

Most editors provide the option of whether to add BOM when setting encoding. When editing PHP files, it is recommended to turn this option off to ensure that the encoding does not automatically add a BOM.

2. Manual editing

If a BOM problem has occurred, it can be solved by manually removing the BOM. Add the following code at the beginning of the PHP file to remove the BOM header:

        

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This code will first use ob_start() to open the output buffer, then output 3 bytes of the BOM, and finally clear the buffer through ob_end_clean().

4. Example of the impact of BOM

Let us demonstrate the impact of BOM on PHP through a simple example. Suppose there is a PHP filetest.phpthat contains a BOM header:

        

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When this file is accessed, it will output:

Hello, World!

However, if the file contains BOM header, that is:


        

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Then the browser will output:

Hello, World!

This extra BOM character will not have a direct impact on the output result, but it may cause a problem in actual applications. series of potential problems.

To sum up, PHP bom refers to the byte order mark located at the beginning of the file, which will cause some potential problems in PHP development, including repeated output of headers. Through editor settings and manual removal of BOM headers, we can avoid and solve these problems and ensure the normal operation of PHP code.

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