Five Common PHP Bad Mistakes and Their Causes

When programming with PHP, you will inevitably encounter some common errors. These errors will not only prevent the program from running normally, but will also affect the stability of the entire application system. This article will introduce five common bad PHP errors, their causes, and provide solutions.

1. Undefined variable

In PHP programming, when an undefined variable is used, an "Undefined variable" error will occur. This error usually occurs when a variable is called or used without defining it ahead of time. For example, the following example:

<? php
echo $name;
?>

The above code will throw an "Undefined variable" error because the variable $name is not defined in the code.

Solution:

Before using a variable, make sure the variable has been defined. This problem can be solved by declaring a variable or assigning an initial value to the variable. For example:

<? php
$name = "Tom";
echo $name;
?>

2. Fatal error: Call to undefined function

This error usually occurs when trying to call a function that does not exist, as shown below:

<? php
test();
?>

The "Fatal error: Call to undefined function" error will be thrown at this time. This error message indicates that the code is trying to call a function that does not exist.

Solution:

Must confirm whether the function to be used has been defined or exists. If the function does not exist, you can solve the problem by defining the function or importing a file containing the function.

3. Parse error: syntax error

This error usually occurs when programmers make some syntax errors when writing PHP code. For example, the following example:

<? php
if (true){
  echo "true";
else{
  echo "false";
}
?>

Because the correct if statement is not written in this code block, the "Parse error: syntax error" error will be thrown.

Solution:

When writing PHP code, you must pay attention to the correctness of the syntax. It is recommended to use a code editor for development.

4. Can't use method return value in write context

This error usually occurs when trying to use a function or method return value to change data, and this operation is not Allowed. For example:

<? php
if (strlen(getName()) > 5){
  // do something
}
?>

The above code will throw the "Can't use method return value in write context" error because the getName() method is used in the strlen() function.

Solution:

Use a temporary variable to store this return value before performing the operation. For example:

<? php
$name = getName();
if (strlen($name) > 5){
  // do something
}
?>

5. Warning: mysqli_connect()

When connecting to the MySQL database, this error usually occurs when the user name or password is incorrect. For example:

<? php
$conn = mysqli_connect('localhost', 'username', 'password');
?>

The "Warning: mysqli_connect()" error will be thrown at this time.

Solution:

Make sure that the MySQL username and password are correct, and check whether the MySQL service has been started before connecting. If the MySQL service does not start, you can solve the problem by starting the MySQL service.

Summary

In PHP programming, common bad mistakes are often caused by programmer's negligence, neglect of details and incorrect code syntax. For these common errors, programmers can solve the problems by carefully checking the code and debugging the code. Relevant error tips and solutions can help programmers locate and fix problems in the code more quickly.

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