检查特定输入文件是否为空

您可以使用数组上的字段进行检查，如下所示：size$_FILES

if ($_FILES['cover_image']['size'] == 0 && $_FILES['cover_image']['error'] == 0)
{
    // cover_image is empty (and not an error)
}

（我还在此处检查错误，因为如果出现问题，它可能是0。我不会为此检查使用名称，因为它可以被覆盖）

方法 1

if($_FILES['cover_image']['name'] == "") {
// No file was selected for upload, your (re)action goes here
}

方法 2

if($_FILES['cover_image']['size'] == 0) {
// No file was selected for upload, your (re)action goes here
}