


Solutions to inaccurate floating point calculation comparison and rounding in PHP, inaccurate rounding_PHP Tutorial
The solution to inaccurate floating point calculation comparison and rounding in PHP, inaccurate rounding
Comparison of floating point calculation results
An example of floating point calculation is as follows:
$a = 0.2+0.7;
$b = 0.9;
var_dump($a == $b);
The printed result is: bool(false). In other words, the calculation result of 0.2+0.7 here is not equal to 0.9, which is obviously against our common sense.
Regarding this issue, the official PHP manual once stated: Apparently a simple decimal fraction such as 0.2 cannot be converted to an internal binary format without losing a little precision. This has to do with the fact that it is impossible to express certain decimal fractions exactly with a finite number of digits. For example, 1/3 in decimal becomes 0.3333333….
We print the above variables in double precision format:
$a = 0.2+0.7;
$b = 0.9;
printf("%0.20f", $a);
echo '
';
printf("%0.20f", $b);
The output results are as follows:
0.89999999999999991118
0.90000000000000002220
Obviously here, as floating-point data, part of its accuracy has been lost and cannot reach complete accuracy. So never trust that a floating-point number result is accurate to the last digit, and never compare two floating-point numbers for equality. It should be noted that this is not a problem with PHP, but a problem with the computer's internal processing of floating point numbers! The same problem will be encountered in languages such as C and JAVA.
So to compare two floating point numbers, we need to control them within the precision range we need before comparing, so use the bcadd() function to add the floating point numbers and convert the precision (to a string):
var_dump(bcadd(0.2,0.7,1) == 0.9); // Output: bool(true)
Floating point number rounding
In the article "PHP Rounding Functions Ceil and Floor", there is an example:
echo ceil(2.1/0.7); // Output: 4
?>
After the above discussion on floating-point number calculations, we know that this is caused by the inaccurate floating-point number calculation results:
printf("%0.20f", (2.1/0.7)); // Output: 3.00000000000000044409
?>
After the above discussion on floating point number calculation, we know that this is caused by the inaccurate floating point number calculation result, so we can use the round() function to deal with it:
echo ceil( round((2.1/0.7),1) );
?>
Although the round() function rounds according to the specified precision, retaining one decimal place has no effect on our rounding result.

Setting session cookie parameters in PHP can be achieved through the session_set_cookie_params() function. 1) Use this function to set parameters, such as expiration time, path, domain name, security flag, etc.; 2) Call session_start() to make the parameters take effect; 3) Dynamically adjust parameters according to needs, such as user login status; 4) Pay attention to setting secure and httponly flags to improve security.

The main purpose of using sessions in PHP is to maintain the status of the user between different pages. 1) The session is started through the session_start() function, creating a unique session ID and storing it in the user cookie. 2) Session data is saved on the server, allowing data to be passed between different requests, such as login status and shopping cart content.

How to share a session between subdomains? Implemented by setting session cookies for common domain names. 1. Set the domain of the session cookie to .example.com on the server side. 2. Choose the appropriate session storage method, such as memory, database or distributed cache. 3. Pass the session ID through cookies, and the server retrieves and updates the session data based on the ID.

HTTPS significantly improves the security of sessions by encrypting data transmission, preventing man-in-the-middle attacks and providing authentication. 1) Encrypted data transmission: HTTPS uses SSL/TLS protocol to encrypt data to ensure that the data is not stolen or tampered during transmission. 2) Prevent man-in-the-middle attacks: Through the SSL/TLS handshake process, the client verifies the server certificate to ensure the connection legitimacy. 3) Provide authentication: HTTPS ensures that the connection is a legitimate server and protects data integrity and confidentiality.

What’s still popular is the ease of use, flexibility and a strong ecosystem. 1) Ease of use and simple syntax make it the first choice for beginners. 2) Closely integrated with web development, excellent interaction with HTTP requests and database. 3) The huge ecosystem provides a wealth of tools and libraries. 4) Active community and open source nature adapts them to new needs and technology trends.

PHP and Python are both high-level programming languages that are widely used in web development, data processing and automation tasks. 1.PHP is often used to build dynamic websites and content management systems, while Python is often used to build web frameworks and data science. 2.PHP uses echo to output content, Python uses print. 3. Both support object-oriented programming, but the syntax and keywords are different. 4. PHP supports weak type conversion, while Python is more stringent. 5. PHP performance optimization includes using OPcache and asynchronous programming, while Python uses cProfile and asynchronous programming.

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.


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