PHP Notice: Undefined offset: 1 with array when reading data

I am getting this PHP error:

PHP Notice:  Undefined offset: 1

Here is the PHP code that throws it:

$file_handle = fopen($path."/Summary/data.txt","r"); //open text file
$data = array(); // create new array map

while (!feof($file_handle) ) {
	$line_of_text = fgets($file_handle); // read in each line
	$parts = array_map('trim', explode(':', $line_of_text, 2)); 
	// separates line_of_text by ':' trim strings for extra space
	$data[$parts[0]] = $parts[1]; 
	// map the resulting parts into array 
	//$results('NAME_BEFORE_:') = VALUE_AFTER_:
}

What does this error mean? What causes this error?

Change

$data[$parts[0]] = $parts[1];

to

if ( ! isset($parts[1])) {
   $parts[1] = null;
}

$data[$parts[0]] = $parts[1];

or simply:

$data[$parts[0]] = isset($parts[1]) ? $parts[1] : null;

Not every line of your file has a colon in it and therefore explode on it returns an array of size 1.

According to php.net possible return values from explode:

> Returns an array of strings created by splitting the string parameter on boundaries formed by the delimiter. > > If delimiter is an empty string (""), explode() will return FALSE. If delimiter contains a value that is not contained in string and a negative limit is used, then an empty array will be returned, otherwise an array containing string will be returned.

How to reproduce the above error in PHP:

php> $yarr = array(3 => 'c', 4 => 'd');

php> echo $yarr[4];
d

php> echo $yarr[1];
PHP Notice:  Undefined offset: 1 in 
/usr/local/lib/python2.7/dist-packages/phpsh/phpsh.php(578) : 
eval()'d code on line 1

What does that error message mean?

It means the php compiler looked for the key 1 and ran the hash against it and didn't find any value associated with it then said Undefined offset: 1

How do I make that error go away?

Ask the array if the key exists before returning its value like this:

php> echo array_key_exists(1, $yarr);

php> echo array_key_exists(4, $yarr);
1

If the array does not contain your key, don't ask for its value. Although this solution makes double-work for your program to "check if it's there" and then "go get it".

Alternative solution that's faster:

If getting a missing key is an exceptional circumstance caused by an error, it's faster to just get the value (as in echo $yarr[1];), and catch that offset error and handle it like this: https://stackoverflow.com/a/5373824/445131

Update in 2020 in Php7:

there is a better way to do this using the Null coalescing operator by just doing the following:

$data[$parts[0]] = $parts[1] ?? null;

This is a "PHP Notice", so you could in theory ignore it. Change php.ini:

error_reporting = E_ALL & ~E_NOTICE & ~E_STRICT & ~E_DEPRECATED

To

error_reporting = E_ALL & ~E_NOTICE

This show all errors, except for notices.

my quickest solution was to minus 1 to the length of the array as

  $len = count($data);
    
    for($i=1; $i<=$len-1;$i++){
      echo $data[$i];
    }

my offset was always the last value if the count was 140 then it will say offset 140 but after using the minus 1 everything was fine

The ideal solution would be as below. You won't miss the values from 0 to n.

$len=count($data);
for($i=0;$i<$len;$i++)
     echo $data[$i]. "<br>";

In your code: $parts = array_map('trim', explode(':', $line_of_text, 2)); You have ":" as separator. If you use another separator in file, then you will get an "Undefined offset: 1" but not "Undefined offset: 0" All information will be in $parts[0] but no information in $parts[1] or [2] etc. Try to echo $part[0]; echo $part[1]; you will see the information.

I just recently had this issue and I didn't even believe it was my mistype:

Array("Semester has been set as active!", true)
Array("Failed to set semester as active!". false)

And actually it was! I just accidentally typed "." rather than ","...

The output of the error, is because you call an index of the Array that does not exist, for example

$arr = Array(1,2,3);
echo $arr[3]; 
// Error PHP Notice:  Undefined offset: 1 pointer 3 does not exist, the array only has 3 elements but starts at 0 to 2, not 3!