Common php error

What are the syntax errors?

PHP belongs to the C-style and imperative programming languages. It has rigid grammar rules, which it cannot recover from when encountering misplaced symbols or identifiers. It can’t guess your coding intentions.

Most important tips

There are a few basic precautions you can always take:

• Use proper code indentation, or adopt any lofty coding style.
  Readability prevents irregularities.

• Use an IDE or editor for PHP with syntax highlighting.
  Which also help with parentheses/bracket balancing.

  

• Read the language reference and examples in the manual.
  Twice, to become somewhat proficient.

How to interpret parser errors

A typical syntax error message reads:

Parse error: syntax error, unexpected T_STRING, expecting ‘;‘ in file.php on line 217

Which lists the possible location of a syntax mistake. See the mentioned file name and line number.

A moniker such as T_STRING explains which symbol the parser/tokenizer couldn’t process finally. This isn’t necessarily the cause of the syntax mistake, however.

It’s important to look into previous code lines as well. Often syntax errors are just mishaps that happened earlier. The error line number is just where the parser conclusively gave up to process it all.

Solving syntax errors

There are many approaches to narrow down and fix syntax hiccups.

• Open the mentioned source file. Look at the mentioned code line.

  • For runaway strings and misplaced operators, this is usually where you find the culprit.

  • Read the line left to right and imagine what each symbol does.

• More regularly you need to look at preceding lines as well.

  • In particular, missing ; semicolons are missing at the previous line ends/statement. (At least from the stylistic viewpoint. )

  • If { code blocks } are incorrectly closed or nested, you may need to investigate even further up the source code. Use proper code indentation to simplify that.

• Look at the syntax colorization!

  • Strings and variables and constants should all have different colors.

  • Operators +-*/. should be tinted distinct as well. Else they might be in the wrong context.

  • If you see string colorization extend too far or too short, then you have found an unescaped or missing closing " or ' string marker.

  • Having two same-colored punctuation characters next to each other can also mean trouble. Usually, operators are lone if it’s not ++, --, or parentheses following an operator. Two strings/identifiers directly following each other are incorrect in most contexts.

• Whitespace is your friend.
  Follow any coding style.

• Break up long lines temporarily.

  • You can freely add newlines between operators or constants and strings. The parser will then concretize the line number for parsing errors. Instead of looking at the very lengthy code, you can isolate the missing or misplaced syntax symbol.

  • Split up complex if statements into distinct or nested if conditions.

  • Instead of lengthy math formulas or logic chains, use temporary variables to simplify the code. (More readable = fewer errors.)

  • Add newlines between:

    1. The code you can easily identify as correct,
    2. The parts you’re unsure about,
    3. And the lines which the parser complains about.

    Partitioning up long code blocks really helps to locate the origin of syntax errors.

• Comment out offending code.

  • If you can’t isolate the problem source, start to comment out (and thus temporarily remove) blocks of code.

  • As soon as you got rid of the parsing error, you have found the problem source. Look more closely there.

  • Sometimes you want to temporarily remove complete function/method blocks. (In case of unmatched curly braces and wrongly indented code.)

  • When you can’t resolve the syntax issue, try to rewrite the commented out sections from scratch.

• As a newcomer, avoid some of the confusing syntax constructs.

  • The ternary ? : condition operator can compact code and is useful indeed. But it doesn’t aid readability in all cases. Prefer plain if statements while unversed.

  • PHP’s alternative syntax (if:/elseif:/endif;) is common for templates, but arguably less easy to follow than normal { code } blocks.

• The most prevalent newcomer mistakes are:

  • Missing semicolons ; for terminating statements/lines.

  • Mismatched string quotes for " or ' and unescaped quotes within.

  • Forgotten operators, in particular for the string . concatenation.

  • Unbalanced ( parentheses ). Count them in the reported line. Are there an equal number of them?

• Don’t forget that solving one syntax problem can uncover the next.

  • If you make one issue go away, but other crops up in some code below, you’re mostly on the right path.

  • If after editing a new syntax error crops up in the same line, then your attempted change was possibly a failure. (Not always though.)

• Restore a backup of previously working code, if you can’t fix it.

  • Adopt a source code versioning system. You can always view a diff of the broken and last working version. Which might be enlightening as to what the syntax problem is.
    

• Invisible stray Unicode characters: In some cases, you need to use a hexeditor or different editor/viewer on your source. Some problems cannot be found just from looking at your code.

  • Try grep --color -P -n "[x80-xFF]" file.php as the first measure to find non-ASCII symbols.

  • In particular BOMs, zero-width spaces, or non-breaking spaces, and smart quotes regularly can find their way into the source code.

• Take care of which type of linebreaks are saved in files.

  • PHP just honors n newlines, not r carriage returns.

  • Which is occasionally an issue for MacOS users (even on OS  X for misconfigured editors).

  • It often only surfaces as an issue when single-line // or # comments are used. Multiline /*...*/ comments do seldom disturb the parser when linebreaks get ignored.

• If your syntax error does not transmit over the web:
  It happens that you have a syntax error on your machine. But posting the very same file online does not exhibit it anymore. Which can only mean one of two things:

  • You are looking at the wrong file!

  • Or your code contained invisible stray Unicode (see above).
    You can easily find out: Just copy your code back from the web form into your text editor.

• Check your PHP version. Not all syntax constructs are available on every server.

  • php -v for the command line interpreter

  • <?php phpinfo(); for the one invoked through the webserver.

  Those aren’t necessarily the same. In particular when working with frameworks, you will them to match up.

• Don’t use PHP’s reserved keywords as identifiers for functions/methods, classes or constants.

• Trial-and-error is your last resort.

If all else fails, you can always google your error message. Syntax symbols aren’t as easy to search for (Stack Overflow itself is indexed by SymbolHound though). Therefore it may take looking through a few more pages before you find something relevant.

Further guides:

• PHP Debugging Basics by David Sklar
• Fixing PHP Errors by Jason McCreary
• PHP Errors – 10 Common Mistakes by Mario Lurig
• Common PHP Errors and Solutions
• How to Troubleshoot and Fix your WordPress Website
• A Guide To PHP Error Messages For Designers — Smashing Magazine

White screen of death

If your website is just blank, then typically a syntax error is the cause.
Enable their display with:

• error_reporting = E_ALL
• display_errors = 1

In your php.ini generally, or via .htaccess for mod_php,
or even .user.ini with FastCGI setups.

Enabling it within the broken script is too late because PHP can’t even interpret/run the first line. A quick workaround is crafting a wrapper script, say test.php:

<?php
   error_reporting(E_ALL);
   ini_set("display_errors", 1);
   include("./broken-script.php");

Then invoke the failing code by accessing this wrapper script.

It also helps to enable PHP’s error_log and look into your webserver’s error.log when a script crashes with HTTP 500 responses.

Common PHP 8.0 Compilation Error Messages

With PHP 8.0 closing on us, it is high time to check our code bases to see if they compile, at least. Here is a list of common PHP 8.0 compilation messages, and what do to with them.

The errors have been found on a corpus of 1756 PHP projects. Any emitted error was compared to the result of the PHP 7.4 compilation. This means that those errors are fatal in PHP 8, while they were absent, or a warning in PHP 7.4. In both cases, in PHP 7.4, it used to be possible to brush them under the carpet, but not in PHP 8.0 anymore.

Common PHP 8.0 compilation errors

• Array and string offset access syntax with curly braces is no longer supported
• Unparenthesized a ? b : c ? d : e is not supported. Use either (a ? b : c) ? d : e or a ? b : (c ? d : e)
• __autoload() is no longer supported, use spl_autoload_register() instead
• Cannot use ‘parent’ when current class scope has no parent
• syntax error, unexpected ‘match’
• The (real) cast has been removed, use (float) instead
• The (unset) cast is no longer supported
• Declaration of A2::B($c, $d = 0) must be compatible with A1::B(&$c, $d = 0)
• Unterminated comment starting line

Array and string offset access syntax with curly braces is no longer supported

Array and string offset access syntax with curly braces is no longer supportedmeans that only the square bracket syntax is now valid.

 
<?php 
   $array = range(0, 10); 
  echo $array{3}; // 4 
?> 

Replace the { with [, and the code will be good again. Exakat spots those with the rule No more curly arrays.

Unparenthesized a ? b : c ? d : e is not supported. Use either (a ? b : c) ? d : e or a ? b : (c ? d : e)

Introduced in PHP 7.4, it is not possible to nest ternary operators. This is related to ternary being right associative, while most of the operators are left associative. PHP RFC: Deprecate left-associative ternary operators.

 
<?php 
1 ? 2 : 3 ? 4 : 5; // deprecated 
(1 ? 2 : 3) ? 4 : 5; // ok 
1 ? 2 : (3 ? 4 : 5); // ok 
?> 

The error message is quite verbose : take advantage of it! Add some parenthesis, or even , split the nested operation into independent expressions. Exakat spots those with the rule Nested Ternary Without Parenthesis.

__autoload() is no longer supported, use splautoloadregister() instead

This error message might appear here thanks to very old applications. Or if they try to support very old PHP versions. In any case, the message is self-explanatory.

Cannot use ‘parent’ when current class scope has no parent

Using the parent keyword in a class without parent, a.k.a. without extends keyword, used to be a Deprecation Notice. In fact, the class would blow up during execution with a ‘Cannot access parent:: when current class scope has no parent’ Fatal error.

It is now a Fatal error at linting time. This will shorten significantly the time between the bug creation and its discovery.

 <?php 
class x { 
   function foo() { 
      echo parent::a; 
   } 
}

(new x)->foo(); 
?> 

As for the fix, there are lots of options, depending on how this parent keyword ended up there in the first place. Exakat spots those with the rule Class Without Parent.

syntax error, unexpected ‘match’

This is a consequence of the introduction of the match instruction in PHP. It is not possible to use that name in instantiation (new), use expressions, instanceof, typehints, functions, classes, interfaces, traits or constants. It is still OK inside a namespace, or for a variable name.

 <?php

// This Match is still valid, thanks to the new Qualified Name processing 
use PeridotLeoMatcherMatch;

// This Match is invalid 
function foo(Match $match) { 
   // do something 
}

// Match side effect : syntax error, unexpected ',' 
$result = match($content,"'KOD_VERSION','(.*)'");

?>

When match is used as a function name, it may lead to an error about commas : the main argument of the new match keyword only accept one argument, so no comma.

The only solution is to rename the classes, interfaces, traits, functions or constants with another name and update the use expressions accordingly.

The (real) cast has been removed, use (float) instead

All is said here. (real) is gone, long live (float).

 
<?php 
  $price = (real) getActualPrice(); 
?> 

Just replace (real) by (float). While you’re at it, you can replace is_real() by is_float() : is_real() didn’t make it into PHP 8.0. Exakat spots those with the rule Avoid Real.

The (unset) cast is no longer supported

The big brother of the unset function is a type cast (unset). It used to be actually the typecast (null) (not in name, but in usage). Very little new about this, and it is a good thing : it is gone for good.

 
<?php 
   (unset) $foo; 
?> 

Exakat spots those with the rule Cast unset usage.

Declaration of A2::B($c, $d = 0) must be compatible with A1::B(&$c, $d = 0)

Checking for method compatibility used to be a warning in PHP 7, and it is now a Fatal error at linting time. The method signature in a parent and its child class must be compatible. It means a lot of different things, depending on visibility, reference, typehint, default values. It is worth a whole article by itself.

The important part is three folds : first, PHP 8.0 emits a Fatal error at compile time for that. So, your PHP 7.0 may hurt on 8.0. If you can fix it now.

 
<?php 
class A1 { 
   function B(&$c, $d = 0) {} 
}

class A2 extends A1 { 
  function B($c, $d = 0) {} 
}

?> 

The second important part is that it only works when PHP lints both classes (parent and child), in the same file, and in the right order : parent first, child second. Otherwise, PHP will only check the compatibility at execution time, and deliver a Fatal error at the worst moment.

The third important part is that compatibility between method signature doesn’t cover argument names. The following code is valid, and a major sleeping bug. Just notice that the variables have been swapped.

 
<?php 
class A1 { 
   function B($c, $d = 0) {} 
}

class A2 extends A1 { 
   function B($d, $c = 0) {} 
}

?> 

Exakat spots those with the following rules Incompatible Signature Methods, and Swapped arguments.

Unterminated comment starting line

Unterminated comment starting line used to be a warning. It is now a parse error.

 
<?php 
/** I always start, but never finish...

Just close the comment, and the code will be good again.

Compile with PHP 8.0 now!

PHP 8.0 moved a significant number of messages from Notice to Fatal errors, and, more importantly, from the execution phase to linting phase. This means that checking your current code with PHP 8.0 is sufficient to bring light on quirky pieces of code that will raise error when you want to upgrade to PHP 8.0. Simply fixing them will also improve your PHP 7.x code!

In the meantime, linting is as fast as it is superficial : it processes files individually, and postpone until execution some of the checks. Static analysis tools cover those situations, and report very early potential bugs and inconsistencies.

Install exakat and run the Migration audit on your code to get even better prepared for the Great Apparition of PHP 8.0. See you next month!

A very large percentage of errors are actually quite simple to spot and solve once you are sufficiently experienced.Some of the mistakes are very basic, but trip up even the best PHP programmer. This article highlights common php errors that developers need to beware of.so that you can write error free and clean code . The main think needs to remember while you are doing code is always turn on your error display with

ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

However, this doesn’t make PHP to show parse errors – the only way to show those errors is to modify your php.ini with this line.

display_errors = on

1)Memory Exhausted Error: This error will display if any of your function or script is eating your memory . you’ve encountered this error when you see this error message.

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 2348617 bytes) in /home4/xxx/public_html/check.php on line xxx

Solution The error can be resolved with a simple trick

define ('wp_memory_limit', '64M');

2)Warning: Cannot modify header information:The page/output always follows the headers.Functions that send/modify HTTP headers must be invoked before any output is made. Otherwise the call fails and you will see the following warning screen.

Warning: Cannot modify header information – headers already sent by (output started at /path/check.php:125) in /path/check2.php on line 15

why headers must be sent before output:
To understand why headers must be sent before output it’s necessary to look at a typical HTTP response. PHP scripts mainly generate HTML content, but also pass a set of HTTP/CGI headers to the webserver:

HTTP/1.1 200 OK
Powered-By: PHP/5.3.7
Vary: Accept-Encoding
Content-Type: text/html; charset=utf-8
<html><head><title>page titlw</title></head>
<body><h1>page content </h1> <p>page output by php code blaaaaah blaaaaaaaaaah...</p>
and <a href="/"> <img src=internal-icon-delayed> </a>

The page/output always follows the headers. PHP has to pass the headers to the webserver first. It can only do that once. After the double linebreak it can nevermore amend them.

When PHP receives the first output (print, echo,) it will flush all collected headers. Afterwards it can send all the output it wants. But sending further HTTP headers is impossible then.
Cause
1) Whitespace before blocks.
3) Whitespace after ?>
4) Preceding error messages
If another PHP statement or expression causes a warning message or notice being printeded out, that also counts as premature output.

3) Cannot redeclare function: This error screen will visible if you are defining a function second time . may be this function is defined in php library or you define this two time . or you are including file contains this function two time . The error message will look like .

Fatal error: Cannot redeclare functiondemo() (previously declared in /home/u805727311/public_html/wp-includes/functions.php:1684) in /home/u805727311/public_html/path/includes/xyz.php on line XXX

4) Internal Server ErrorThis is the most common error message . The most likely issue is a corrupted .htaccess file. So first of all check your .htaccess file . secondly try to increaso your php memory limit with .

define ('wp_memory_limit', '64M');

5)Call to undefined function:This error will display if you are calling an undefined function or calling a defined function with wrong name . I.e if you are calling is_array() as isarray() then php will throw a fatal error that function is not defined . The error message is

[01-Jun-2011 14:25:15] PHP Fatal error: Call to undefined function myfunction() in /home/accountname/public_html/your user/file/index.php on line 7

6)Unexpected string:If you are receiving an error which says ‘parse error: unexpected’ this usually means that you have forgotten to include a character. The most common are:

Unexpected ‘=’ : you have forgotten to include the $ when referencing a variable
Unexpected ‘)’ : you have forgotten to include the opening bracket (
Unexpected ‘(‘ : you have forgotten to include the closing bracket )
Unepxpected T_STRING: you have forgotten a quotation mark or a semi-colon at the end of the previous line
Unexpected T_ELSE: you have an else statement with no opening if statement

7)Maximum execution time exceeded : You may receive a message such as “Maximum execution time of 30 seconds exceeded” or “Maximum execution time of 60 seconds exceeded”. This means that it is taking to longer for a process to complete and it is timing out. There are a number of ways to fix this error.solution to this error is either set the execution time at run time with ini_set() or edit your php.ini file to set this

ini_set('max_execution_time', 1000);

8)Use of an undefined constant:As with parse errors, “use of an undefined constant” means that you are missing a character. It could be one of the following:

Missing a $ when referencing a viariable
Missing quotation marks around array keys

9)only variable should pass by reference:Assign the result of explode to a variable and pass that variable to end:

$file_extension = end(explode('.', $file_name));

if you are using the above code it will throw this error .The problem is, that end requires a reference, because it modifies the internal representation of the array (i.e. it makes the current element pointer point to the last element).
The result of explode(‘.’, $file_name) cannot be turned into a reference. This is a restriction in the PHP language, that probably exists for simplicity reasons.

$tmp = explode('.', $file_name);
$file_extension = end($tmp);

10)Undefined index:If you are getting an element from array in which the called index does’t exist then that is an error .The error looks like this

Undefined variable: user_location in C:wampwwwmypathindex.php on line 12

Solution for this problem is
Recommended: Declare your variables. Or use isset() to check if they are declared before referencing them, as in:

$value = isset($_POST['value']) ? $_POST['value'] : '';.

Use empty(), so no warning is generated if the variable does not exist. It’s equivalent to !isset($var) || $var == false. E.g.

echo "Hello " . (!empty($user) ? $user : "");