如何检查数组中是否存在给定的键或索引？

I have created an array of data from mysql database. This is how that array looks like:

// Fetch all the records:
while ($stmt->fetch()) {

    $output  =  "<a>
";
    $output .=      "<h3>{$product_name}</h3>
";
    $output .=      "<span class='price'><span class='amount'>BD.{$price}</span></span>
";
    $output .=  "</a>
";
    $output .=  "<div class='short_desc'>
";
    $output .=          "$product_des
";       
    $output .=  "</div>
";

    //Add output to array
    $products[] = $output;      
}

Since I want to use this array values from outside my while loop and This is how I use this $products[] array in my page.

echo $products[0];
echo $products[1];
echo $products[2];
echo $products[3];

My question is if this $products[] array have one result set I can get an error.

My error message is like this: An error occurred in script 'C:\wamp\www\Computer\index.php' on line 208: Undefined offset: 2

So I tried to fix this problem using array_key_exists() function like this way for each echo:

if(!empty($products) && array_key_exists("$products[1]", $products)) echo $products[1]; else echo "No Product";

But still I can get error. Can anybody tell me what is wrong with this?

Thank you.

You probably want something like:

if( ! empty($products) ) {
    $ids = array(0, 1, 2, 3, 4, 5);
    foreach ( $ids as $id ) { 
      if ( ! empty($products[$id]) ) echo $products[$id];
    }
} else { 
   echo "No Product";
}

The function array_key_exists() has, according to the documentation, a signature of:

bool array_key_exists ( mixed $key , array $array )

That is to say: It will return bool (TRUE or FALSE) if the $key (index, would be 1 through 5 in your case) exists in $array.

Therefore, the accepted syntax for your case is:

array_key_exists(1, $products)

HOWEVER, perhaps more straight-forward would be the use of empty() or isset(), both of which will work in your situation as:

if (!empty($products[0])) echo $products[0];
// ...
if (!empty($products[5])) echo $products[5];

Or:

if (isset($products[0])) echo $products[0];
// ...
if (isset($products[5])) echo $products[5];

It would also be possible to do a loop, including HTML, and stay sane:

<!-- PRE-HTML -->

<?php if(!empty($products)) foreach((array) $products as $product) { ?>

    <!-- Product-Specific PRE-HTML -->

    <?php echo $product ?>

    <!-- Product-Specific POST-HTML -->

<?php } /* End for loop */ ?>

<!-- POST-HTML -->

If you want to access a single index within your array, without getting a notice, you have to check, if the key exists.

You might use isset (http://php.net/manual/de/function.isset.php):

if(isset($products[0]))
{
  echo "yes, the key 0 is set within $products"; 
}

If you want to take all the entries, within your array, use foreach.

foreach($products as $product)
{
 echo $product; 
}