In what situations should PHP developers use functions like iconv to convert character encoding, especially when dealing with text files from external sources?

When dealing with text files from external sources, PHP developers should use functions like iconv to convert character encoding when the file's encoding doesn't match the expected encoding of the application. This is important to ensure that the text is displayed correctly and prevent issues like garbled text or encoding errors.

// Specify the input and output encodings
$input_encoding = 'ISO-8859-1';
$output_encoding = 'UTF-8';

// Read the contents of the text file
$file_contents = file_get_contents('external_file.txt');

// Convert the encoding using iconv
$converted_contents = iconv($input_encoding, $output_encoding, $file_contents);

// Output the converted contents
echo $converted_contents;