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The Output Control function allows you to freely control the output of data in the script. It is very useful, especially when you want to output the file header after the data has been output. The output control function does not affect the file header information sent using header() or setcookie(), only the data blocks similar to echo() and PHP code.
Let’s give a simple example first to give everyone a general impression of Output Control:
Example 1.
ob_start(); //Open the buffer
echo "Hellon"; //Output
header("location:index.php"); //Redirect the browser to index.php
ob_end_flush(); //Output all content to the browser
?>
Everyone who knows the header() function knows that this function will send a file header to the browser, but if there is any output before using this function (including empty output, such as spaces , carriage return and line feed) will prompt an error. If we remove ob_start() in the first line and then execute this program, we will find that we get an error message: "Header had all ready send by"! But with ob_start, there will be no error message. The reason is that when the buffer is opened, the characters after echo will not be output to the browser, but will be retained on the server. They will not be output until you use flush or ob_end_flush, so it will not Any file header output errors!
1. Introduction to related functions:
1. Flush: refresh the contents of the buffer and output.
Function format: flush()
Description: This function is frequently used and is very efficient.
2. ob_start: Open the output buffer
Function format: void ob_start(void)
Description: When the buffer is activated, all non-file header information from the PHP program will not be sent, but saved. in the internal buffer. In order to output the contents of the buffer, you can use ob_end_flush() or flush() to output the contents of the buffer.
3. ob_get_contents: Returns the contents of the internal buffer.
Usage: string ob_get_contents(void)
Description: This function will return the contents of the current buffer. If the output buffer is not activated, it will return FALSE.
4. ob_get_length: Returns the length of the internal buffer.
Usage: int ob_get_length(void)
Description: This function will return the length in the current buffer; the same as ob_get_contents, if the output buffer is not activated. then returns FALSE.
5. ob_end_flush: Send the contents of the internal buffer to the browser and close the output buffer.
Usage: void ob_end_flush(void)
Description: This function sends the contents of the output buffer (if any).
6. ob_end_clean: Delete the contents of the internal buffer and close the internal buffer
Usage: void ob_end_clean(void)

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