Why Does My Recursive PHP Barcode Generator Sometimes Return 'Not Set'?

How to Handle Recursion and Result Retrieval in PHP

Question:

To generate unique barcodes, a recursive function is employed to ensure no duplicate entries exist in the database. However, the function sometimes returns "Not Set" instead of a unique number. Determine the cause and provide a fix for the flawed code below:

function generate_barcode() {
    $barcode = rand(1, 10);
    $bquery = mysql_num_rows(mysql_query("SELECT * FROM stock_item WHERE barcode='$barcode'"));
    if ($bquery == 1)
        generate_barcode();
    else
        return $barcode;
}

Answer:

The issue lies within the recursive call's absence of a return statement. This means the function does not return the generated number in that branch of the recursion, potentially leading to "Not Set" errors.

To fix this, modify the recursive call to return the generated number:

function generate_barcode() {
    $barcode = rand(1, 10);
    $bquery = mysql_num_rows(mysql_query("SELECT * FROM stock_item WHERE barcode='$barcode'"));
    if ($bquery == 1)
        return generate_barcode(); // changed!
    else
        return $barcode;
}

Additional Consideration:

To prevent infinite recursion in cases where all numbers are reserved, it is crucial to include a condition that halts the recursion and raises an error, such as:

if ($recursiveCalls > 1000) // or any suitable limit
  throw new Exception('Failed to generate a unique barcode within the specified limit.');

By incorporating these modifications, the function will consistently return unique barcodes and handle the edge case of all numbers being taken.

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