I am using XAMPP on Windows. By printing $_FILES[\"file\"][\"tmp_name\"], it seems that the temporary file was saved at C:\\xampp\\tmp\\phpABCD.tmp. But I cannot se
$_FILES[\"file\"][\"tmp_name\"]
You can check where php is currently saving your temp files $_FILES["file"]["tmp_name"] by printing
files $_FILES["file"]["tmp_name"]
sys_get_temp_dir()