The header jump failure may be caused by four key points. 1.header() must be called before any output, including spaces or echo. It is recommended to use ob_start() to buffer the output; 2. If condition may not be true, check whether the variable is initialized, whether the comparison method is correct, and whether there is a spelling error; 3. Exit or die must be added after the header, otherwise subsequent code execution will affect the jump effect; 4. Check whether there are multiple redirect conflicts to ensure that the jump logic is handled in a unified manner to avoid repeated sending of headers.
In PHP development, sometimes we use header("Location: ...") to jump to the page. But if you write it in an if statement and find that the jump is not effective, it may be because you have ignored several key points.
1. Header() must be called before output
The header() function of PHP must be called before any actual output, otherwise it will fail. This includes HTML tags, spaces, echo output, print output, etc. Even if there is just an empty line in front, it will cause header() to report an error.
Common phenomena:
- There is blank at the top of the page or
<?phphas content in front of it - There is output in the included files (such as debugging information)
Suggested practices:
- Make sure
header()is the first content to be executed in the entire script - Use
ob_start()andob_end_flush()to buffer the output (suitable for complex projects)
<?php
ob_start(); // Turn on output buffering// Subsequent logical processing if ($condition) {
header("Location: https://example.com");
exit;
}
ob_end_flush(); // Finally refresh the buffer?>2. if the judgment conditions are really valid?
Sometimes you think you have entered the if branch, but you actually haven't entered. This is usually because the variable values ??do not meet expectations or the comparison method is incorrect.
Checkpoint:
- Is the variable initialized?
- Is it used loose comparison (
==) instead of strict comparison (===)? - Is there any typo or logic error?
For example:
if ($_POST['submit'] == 'yes') {
header("Location: success.php");
exit;
} If the user does not submit the form or does not have 'submit' => 'yes' in the submitted data, this code will not be executed. You can use var_dump($_POST) to check the current data structure.
3. Be sure to add exit or die after header()
Even if you write header("Location: ...") , if there is still code behind it, the browser may not jump. Because PHP is a server-side language, it will continue to execute the code until it ends.
Correct writing:
if ($loginSuccess) {
header("Location: dashboard.php");
exit; // Prevent subsequent code execution}Not recommended writing:
if ($loginSuccess) {
header("Location: dashboard.php");
}
echo "This will still run!"; Even if the jump is performed, echo will still be executed. The client's behavior is determined by the server's response and may not be stopped immediately.
4. Check for redirection conflicts
If you use header("Location: ...") in multiple places, especially in include files, multiple headers may be sent. At this time, only the first one takes effect, and the subsequent ones will be ignored.
suggestion:
- Unified processing of jump logic to avoid duplication
- Use function to encapsulate jump operations (such as
redirect($url)) - Check whether multiple headers appear in different criteria
Basically these common reasons. When header location does not work, first confirm whether there is any output in advance, then check whether the conditions are true, and finally ensure that exit is executed after jumping. These problems may seem small, but can easily get stuck with newbies.
The above is the detailed content of PHP header location not working in if statement. For more information, please follow other related articles on the PHP Chinese website!
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