curl_exec() always returns false

Error checking and handling is the programmer’s friend. Check the return values of the initializing and executing cURL functions. curl_error() and curl_errno() will contain further information in case of failure:

try {
    $ch = curl_init();

    // Check if initialization had gone wrong*    
    if ($ch === false) {
        throw new Exception('failed to initialize');
    }

    // Better to explicitly set URL
    curl_setopt($ch, CURLOPT_URL, 'http://example.com/');
    // That needs to be set; content will spill to STDOUT otherwise
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    // Set more options
    curl_setopt(/* ... */);
    
    $content = curl_exec($ch);

    // Check the return value of curl_exec(), too
    if ($content === false) {
        throw new Exception(curl_error($ch), curl_errno($ch));
    }

    // Check HTTP return code, too; might be something else than 200
    $httpReturnCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);

    /* Process $content here */

} catch(Exception $e) {

    trigger_error(sprintf(
        'Curl failed with error #%d: %s',
        $e->getCode(), $e->getMessage()),
        E_USER_ERROR);

} finally {
    // Close curl handle unless it failed to initialize
    if (is_resource($ch)) {
        curl_close($ch);
    }
}

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^* The curl_init() manual states:

Returns a cURL handle on success, FALSE on errors.

I’ve observed the function to return FALSE when you’re using its $url parameter and the domain could not be resolved. If the parameter is unused, the function might never return FALSE. Always check it anyways, though, since the manual doesn’t clearly state what “errors” actually are.