切片¶
ID: cpp/slicing
Kind: problem
Security severity:
Severity: warning
Precision: high
Tags:
- reliability
- correctness
- types
Query suites:
- cpp-security-and-quality.qls
此查询查找将派生类型的非引用实例分配给基类型变量的情况，其中派生类型比基类型具有更多字段。这些赋值会切除派生类型添加的所有字段，并在访问为派生类型时导致意外状态。
建议¶
将赋值左侧变量的类型更改为子类。
示例¶
static int idctr = 0;
//Basic connection with id
class Connection {
public:
int connId;
virtual void print_info() {
cout << "id: " << connId << "\n";
}
Connection() {
connId = idctr++;
}
};
//Adds counters, and an overriding print_info
class MeteredConnection : public Connection {
public:
int txCtr;
int rxCtr;
MeteredConnection() {
txCtr = 0;
rxCtr = 0;
}
virtual void print_info() {
cout << "id: " << connId << "\n" << "tx/rx: " << txCtr << "/" << rxCtr << "\n";
}
};
int main(int argc, char* argv[]) {
Connection conn;
MeteredConnection m_conn;
Connection curr_conn = conn;
curr_conn.print_info();
curr_conn = m_conn; //Wrong: Derived MetricConnection assigned to Connection
//variable, will slice off the counters and the overriding print_info
curr_conn.print_info(); //Will not print the counters.
Connection* curr_pconn = &conn;
curr_pconn->print_info();
curr_pconn = &m_conn; //Correct: Pointer assigned to address of the MetricConnection.
//Counters and virtual functions remain intact.
curr_pconn->print_info(); //Will call the correct method MeteredConnection::print_info
}