Types of Errors in PHP and How to Handle Them

In this article, I am going to discuss the Types of Errors in PHP and How to Handle Them.

There are four types of errors that a PHP Script can generate.

Syntax errors or compile errors
Runtime errors or fatal errors
Warnings
Notice Errors

Syntax Errors (Compile Errors)

Syntax errors are those errors that the compiler catches. These errors result from wrong spelling, missing semicolon, not ending the string properly or any other typing mistake. When compiler encounters any such error, it reports these errors as syntax errors. The following code shows syntax errors in lin2 and line 6.

<?php
$a='hello';
$b='world!

echo $a;
echo '<br>';
ech $b;

?>

Output

**A Parse Error Due to Missing apostrophe and semicolon**

When we make correction in line 2 of the above program as $b=’world!’, we get another error. This is due to spelling mistake in echo function in the last line.

**A Parse Error due to Spelling Mistake**

Once we correct both of these errors as follows, we get the following output.

<?php
$a='hello';
$b='world!';

echo $a;
echo '<br>';
echo $b;

?>

Output

Notice Errors

In fact, a notice error may be or may not be an errors. These are minor errors. Furthermore, notice errors don’t stop script and produces the output. The most common source f notice errors are the use of undefined variable. As can be seen in the following code, the variables a, b, and c are not defined. So, when we try to print these variables, a notice error occurs.

<?php
 echo $a.' '.$b.' '.$c;
?>

Output

**Notice Errors Due to the Use of Non-Existing variables**

Runtime Errors (Fatal Errors)

These errors make the script to crash. When a fatal error occurs, the script stops executing. These types of errors result from a number of sources. For instance, call to a non-existing function, or calling a function from an object that doesn’t exist.

Examples on Types of Errors in PHP and How to Handle Them

The following code shows that call to a non-existing function mysqli results in a fatal error.

<?php
 // Try to connect with a MySQL database
 $con1=mysqli("localhost", "root", "", "somedatabase");
?>

Output

**Fatal Error Due to the Use of Undefined Function**

Similarly the following error occurs because of the undefined function show().

<?php
 class MyClass
 {
   protected $a, $b;
 }
 class SubClass extends MyClass{
    function __construct()
    {
       $this->a=1; $this->b=2;
       show();
     }
    function show()
    {
	echo 'a = ', $this->a;
        echo "<br>b = ", $this->b;
    }
  }
  $ob=new SubClass(20, 30);
  $ob->__construct();
?>

Output

**Call to Undefined Function Results in a Fatal Error**

Correcting the Above Error

In order to correct the above error, just call the function show() as the instance method as shown below.

<?php
 class MyClass
 {
   protected $a, $b;
 }
 class SubClass extends MyClass{
    function __construct()
    {
       $this->a=1; $this->b=2;
       $this->show();
     }
    function show()
    {
	echo 'a = ', $this->a;
        echo "<br>b = ", $this->b,'<br>';
    }
  }
  $ob=new SubClass(20, 30);
  $ob->__construct();
?>

Output

**An Example to Show the Types of Errors in PHP and How to Handle Them**

The following fatal error results from the fact that the database table ’emp’ doesn’t exist.

<?php
 // Try to connect with a MySQL database
 $con1=new mysqli("localhost", "root", "", "d1");
 $r1=$con1->query('select * from emp');
 $row = $r1->fetch_assoc()
?>

Output

**Fatal Error Due to Non-availability of the Database Table**

When a recursive function fails to terminate, a runtime error occurs. The following code demonstrates it.

<?php
 function f1()
 {
  $a=$a++;
  echo $a;
  f1();
 }
 f1();
?>

Output

**Fatal Error Due to a Non-Terminating Recursive Function Call**

Warnings

Warnings indicate the presence of some issues. However, they don’t stop execution of script. The following code shows a warning generated when the database user is not able to access a table due to invalid cresentials.

<?php
 // Try to connect with a MySQL database
 $con1=new mysqli("localhost", "someuser", "123456", "somedatabase");
?>

Output

**Warning Generated Due to Access Denied to a User**

Similarly, the following code generates a warning because of invalid database name.

<?php
 // Try to connect with a MySQL database
 $con1=new mysqli("localhost", "root", "", "somedatabase");
?>

Output

**Warning Generated Due to the Use of Unknown Database**

Syntax Errors (Compile Errors)

Notice Errors

Runtime Errors (Fatal Errors)

Examples on Types of Errors in PHP and How to Handle Them

Correcting the Above Error

Warnings

Further Reading

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