PHP error: Solution to using illegal numbers as constant names!

PHP error: Solution to using illegal numbers as constant names!

In the PHP development process, we often use constants to save some values ​​that will not change, such as database connection information, website configuration, etc. The naming of constants must follow certain rules, including not starting with a number. However, sometimes we accidentally use illegal numbers as constant names when defining constants, which will cause PHP to report an error and terminate the execution of the program. This article explains how to solve this problem, along with code examples.

In PHP, define constants using the define() function. The general naming rule for constants is to start with a letter or underscore, and can be followed by any number of letters, numbers, and underscores. However, if we name a constant starting with a number, PHP will report an error and prompt "Constant name must start with a letter or underscore" (constant name must start with a letter or underscore).

The way to solve this problem is to use strings to define constants instead of using illegal numbers. We can use illegal numbers as part of a string as follows:

define('CONST_123', 'Hello, World!');

Constants defined in this way can be used normally without reporting an error. We can use the constant CONST_123 to access the value it holds.

echo CONST_123; // 输出：Hello, World!

This method can ensure the legality of the constant name and allow us to intuitively know the meaning of the constant in other places. At the same time, using strings to define constants has another benefit. Even if we modify the value of the constant later, the places in the code that reference the constant do not need to be modified.

If we need to define a set of number-related constants, we can use an array to achieve it. For example, define a constant array that holds the day of the week:

define('WEEKDAYS', ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']);

This way we can access the elements in the array by index:

echo WEEKDAYS[0]; // 输出：Sunday

Another benefit of using an array to define number-related constants is that you can Loop to access them. For example, we can use a foreach loop to traverse and output the days of the week:

foreach (WEEKDAYS as $index => $weekday) {
    echo $index+1 . ' - ' . $weekday . '<br>';
}

The output results are as follows:

1 - Sunday
2 - Monday
3 - Tuesday
4 - Wednesday
5 - Thursday
6 - Friday
7 - Saturday

Through the above method, we can avoid PHP errors caused by using illegal numbers as constant names. Moreover, using strings or arrays to define constants can also improve the readability and maintainability of your code.

To summarize, when we encounter an error when using illegal numbers as constant names in PHP development, we can solve the problem by using illegal numbers as part of a string or using an array to define constants. These methods not only enable the normal use of constants, but also improve the readability and maintainability of the code.

I hope this article can help you solve problems in PHP development and make your code more stable and efficient. Thanks for reading!

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