mysqli数据库链接的单例对象

class Db {
private static $instance;
public KaTeX parse error: Expected group after '_' at position 28: …ivate function _̲_construct(host,$username,$password,$dbname) {
$this->handle=NULL;
$this->getcon($host,$username,$password,KaTeX parse error: Expected 'EOF', got '}' at position 12: dbname); }̲ public stati…instance=new Db();
return self::KaTeX parse error: Expected 'EOF', got '}' at position 13: instance; }̲ private func…host,$username,$password,KaTeX parse error: Expected '}', got 'EOF' at end of input: …bname) { if(this->handle!=NULL){
return true;
}
$this->handle=mysql{i}_{c}onnect($host,$username,$password,$dbname);
}
}