Completely eliminate PHP session cookie errors_PHP tutorial
As long as you have written PHP code, I believe you have encountered this warning that is puzzling most of the time.. Today we will solve it.............
After reading the PHP manual, the answer is as follows:
The message "Warning: Cannot send session cookie - headers already sent..." or "Cannot add header information - headers already sent...".
The functions header(), setcookie() and session functions need to add header information to the output stream. But header information can only be sent before any other output content. There cannot be any output (such as HTML) before using these functions. The function headers_sent() checks whether your script has sent headers. See "Output Control Functions".
Meaning: Do not use any text, blank lines, carriage returns, spaces, etc. before using the above function. but. . . The problem is, this answer is unsatisfactory. Because often programs run normally in other PHP environments.
First of all: How does this error occur? Let us take a look at how PHP handles HTTP header output and body output.
When the PHP script starts executing, it can send header information and body information at the same time. Header information (from header() or SetCookie() function) is not sent immediately, instead, it is saved to a list. This allows you to modify the header information, including the default header (such as the Content-Type header). However, once the script sends any non-header output (for example, using HTML or a print() call), then PHP must first send all headers and then terminate the HTTP header. Then continue to send the main data. From this point on, any attempt to add or modify header information is not allowed and one of the above error messages will be sent.
Okay! Then let’s solve it:
Stupid method: don’t display any error warnings!
I won’t tell you the specific method ^_^#
Solution:
1) Applicable to those who have permission to edit PHP. INI people
Open php. ini file (you should know your php better than I do. Where is the ini), find
output_buffering = and change it to on or any number. If it is IIS6, please change it to ON, otherwise your PHP efficiency will be extremely slow.
2) Using a virtual host, PHP cannot be edited. INI, what should I do?
Simple:
Create one in the root directory of your space. htaccess file, the content is as follows:
AllowOverride All
PHP_FLAG output_buffering On
The unfortunate situation is: still not working? All web pages cannot be displayed?
Then, you can call the space provider and scold the space provider, and then Ask him to give you apache. Open htaccess AllowOverride
3) Solve it in the PHP file
ob_start()
Enable the output buffering mechanism. Output buffering supports multiple levels - for example, the ob_start() function can be called multiple times.
ob_end_flush()
Send output buffer (output buffer) and disable the output buffering mechanism.
ob_end_clean()
Clear the output buffer without sending it, and disable output buffering.
ob_get_contents()
Return the current output buffer as a string. Allows you to process any output emitted by the script.
Principle:
When output_buffering is enabled, PHP does not send HTTP headers when the script sends output. Instead, it pipes this output into a dynamically growing cache (only available in PHP 4.0, which has a centralized output mechanism). You can still modify/add headers, or set cookies, since headers are not actually sent. When all scripts terminate, PHP will automatically send HTTP headers to the browser, and then send the contents of the output buffer.

PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.

PHP originated in 1994 and was developed by RasmusLerdorf. It was originally used to track website visitors and gradually evolved into a server-side scripting language and was widely used in web development. Python was developed by Guidovan Rossum in the late 1980s and was first released in 1991. It emphasizes code readability and simplicity, and is suitable for scientific computing, data analysis and other fields.

PHP is suitable for web development and rapid prototyping, and Python is suitable for data science and machine learning. 1.PHP is used for dynamic web development, with simple syntax and suitable for rapid development. 2. Python has concise syntax, is suitable for multiple fields, and has a strong library ecosystem.

PHP remains important in the modernization process because it supports a large number of websites and applications and adapts to development needs through frameworks. 1.PHP7 improves performance and introduces new features. 2. Modern frameworks such as Laravel, Symfony and CodeIgniter simplify development and improve code quality. 3. Performance optimization and best practices further improve application efficiency.

PHPhassignificantlyimpactedwebdevelopmentandextendsbeyondit.1)ItpowersmajorplatformslikeWordPressandexcelsindatabaseinteractions.2)PHP'sadaptabilityallowsittoscaleforlargeapplicationsusingframeworkslikeLaravel.3)Beyondweb,PHPisusedincommand-linescrip

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values and handle functions that may return null values.

In PHP, use the clone keyword to create a copy of the object and customize the cloning behavior through the \_\_clone magic method. 1. Use the clone keyword to make a shallow copy, cloning the object's properties but not the object's properties. 2. The \_\_clone method can deeply copy nested objects to avoid shallow copying problems. 3. Pay attention to avoid circular references and performance problems in cloning, and optimize cloning operations to improve efficiency.

PHP is suitable for web development and content management systems, and Python is suitable for data science, machine learning and automation scripts. 1.PHP performs well in building fast and scalable websites and applications and is commonly used in CMS such as WordPress. 2. Python has performed outstandingly in the fields of data science and machine learning, with rich libraries such as NumPy and TensorFlow.


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