The main reason for the failure of header('Location:...') is that it has output before it. 1. Once PHP starts output (such as echo, print, space or line break), the HTTP header is sent and cannot be modified; 2. Typical errors are echo first and then call header; 3. Solutions include ensuring that there is no output before the header and putting redirection at the forefront of the script; 4. Alternative solutions can be used to jump JavaScript, HTML meta refresh or enable output buffering ob_start().
PHP's header('Location: ...') is very direct to use, but if there is already output before it (such as using echo ), there will be problems. This problem is particularly common, especially when newbies write code.
This happens because PHP has already output some content before sending HTTP header information. Once the output starts, the header information cannot be modified, so header('Location: ...') will be invalid and even an error will be reported.
As soon as the output is generated, the header becomes invalid
PHP is parsed and output. The output will be triggered as long as you use echo , print , var_dump , or even spaces or newlines outside the HTML tag. At this time, call header() function again, and an error similar to "Cannot modify header information - headers already sent" will be prompted.
For example:
<?php
echo "Hello";
header("Location: https://example.com"); The above code will not jump, but will report an error. Because echo "Hello" has asked PHP to start sending data to the browser, the header message has been sent out, and it will be too late to change it later.
Solution: Avoid early output
To solve this problem, the most direct way is to ensure that there is no output before header() call. include:
- Do not use echo, print and other output statements before header
- Avoid spaces or line wrapping before PHP tag
<?php - Avoid any content after PHP tag
?>(It is recommended to omit the end tag)
A common practice is to put redirect logic at the front of the script, such as:
<?php
if ($someCondition) {
header("Location: dashboard.php");
exit;
}
// The main body of the page continues to execute echo "Welcome!";This ensures that there is no output interference.
If you can't control the output, you can try these methods
Sometimes when the project structure is complicated or if the content is accidentally output during debugging, you have to take a detour. Here are a few alternatives:
Jump with JavaScript
echo "<script>window.location.href='https://example.com';</script>";
This is not the optimal solution, but it can solve the problem.
Using HTML meta refresh
echo "<meta http-equiv='refresh' content='0;url=https://example.com'>";
The effect is similar to JS and is suitable for simple scenarios.
Turn on output buffering
Enableoutput_bufferingin PHP configuration, or add:ob_start();
In this way, even if you write
echofirst, the content will not be output immediately, and the content will not be output until the call toob_end_flush()or the script is over.
Let's summarize
-
header('Location: ...')must be called before any output - Early output may be caused by
echo, spaces, HTML content, etc. - It is best to put the redirect logic at the front of the script
- If it really doesn't work, you can use JS or meta tags to jump, or enable output buffering.
Basically all this is not complicated but easy to ignore.
The above is the detailed content of PHP header location not working after echo. For more information, please follow other related articles on the PHP Chinese website!
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