Why Does `json_decode()` Return NULL Despite Valid JSON?

json_decode() with Valid JSON: A Case Study

When attempting to decode a JSON object stored in a text file using json_decode(), a scenario may arise where the function returns NULL despite the JSON appearing valid to JSON validators. This can be perplexing since the file is readable and the JSON syntax seems correct.

In such cases, it's recommended to check for non-printable characters that may have crept into the JSON string. These characters can disrupt the decoding process, causing json_decode() to fail.

To resolve this issue, the JSON string can be sanitized using regular expressions to remove these non-printable characters. The following code snippet demonstrates this:

$json_string = preg_replace('/[\x00-\x1F\x80-\xFF]/', '', $json_string);
$json_object = json_decode($json_string, true);

This code replaces all non-printable characters in the $json_string variable with an empty string. The true parameter in json_decode() ensures that the decoded result is returned as an associative array, which might be more convenient for further processing.

By removing the non-printable characters, the sanitized JSON string can be successfully decoded, preventing json_decode() from returning NULL. This ensures that valid JSON data can be reliably converted into a PHP data structure for further usage.

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