How to solve the problem of invalid PHP header?

When developing websites, we often need to use the header() function in PHP. In this article, I will introduce you to the possible failures when using the header() function and provide several kind of solution.

1. The reason why the header() function fails

1. The content has been output before sending the header() function
   No content can be output before using the header() function, otherwise This will cause the header() function to fail. This is because the header() function is used to send HTTP header information. If the page content has been output before sending the HTTP header information, the header() function will not work properly.
2. HTTP header information has been sent
   The header() function can not only send HTTP header information, but also modify HTTP header information. However, if the HTTP header information has already been sent, it cannot be modified.
3. Using the output buffer
   When the output buffer is used, the output content will not be sent to the client immediately, but will be cached on the server first. Therefore, when using the header() function, you need to close the output buffer first.
4. Errors in the program
   If there are syntax errors or logical errors in the program, the header() function will also fail. Therefore, when debugging the program, you need to pay attention to troubleshooting errors.

2. Solution

In response to the above problems, we can adopt the following solutions:

1. Do not output anything before the header() function
   If you want to output some content before the header() function, you can use the ob_start() function to open the output buffer, close the output buffer before the header() function, and clear the content in the buffer. For example:

ob_start();
echo "Hello, world!";
ob_end_clean();
header("Location: https://www.example.com/");

2. Check whether the HTTP header information has been sent before using the header() function
   Before using the header() function, you can use the headers_sent() function to check the HTTP header Whether the external information has been sent. If it has been sent, the HTTP header information cannot be modified.

For example:

if (!headers_sent()) {
    header("Location: https://www.example.com/");
}

3. Close the output buffer
   Before using the header() function, you can close the output buffer first to ensure that the previously output content is Sent to client. You can use the following code to close the output buffer:

if (ob_get_length() > 0) {
    ob_end_flush();
}
header("Location: https://www.example.com/");

4. Troubleshooting errors in the program
   When there are errors in the program, you can use PHP's built-in error handling function for debugging, for example Use the error_reporting() function to set the error reporting level, or use PHP's debugging tools, etc.

Summary
In website development, using the header() function is a very common operation. However, when using the header() function, you need to pay attention not to output content before sending the HTTP header information, check whether the HTTP header information has been sent, close the output buffer, etc. I hope that the introduction in this article can help you better use the header() function.

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