如何修复Valgrind检测到的“条件跳转依赖未初始化值”错误？

示例代码 #

#include <iostream>
using namespace std;

class A{
    int * p;
    public:
        A(){
            cout << "Default Constructor" << endl;
            p = new int[10]{0};
        }
        A(const A& obj){
            cout << "Copy Constructor" << endl;
            p = new int[10]{0};
            for(int i=0;i<10;i++)
                p[i] = obj.p[i];
        }
        A(A&& obj){
            cout << "Move Constructor" << endl;
            delete [] p;
            p = obj.p;
            obj.p = nullptr;
        }

        A& operator = (const A & obj){
            cout << "Copy Assignment Operator " <<endl;
            if(this == &obj)
                return *this;

            p = new int[10]{0};
            for(int i = 0 ;i < 10;i++)
                p[i] = obj.p[i];

            return *this;    
        }

        A& operator = (A&& obj){
            cout << "Move Assignment Operator" <<endl;
            if(this == &obj)
                return *this;

            delete [] p;
            p = obj.p;
            obj.p = nullptr;

            return *this;    
        }

        ~A(){
            cout << "Destructor " << endl;
            delete [] p;
        }
        void setData(){
            for(int i = 0 ; i < 10 ;i++)
                p[i] = i*i;
        }
        void printData(){
            for(int i=0;i<10;i++)
                cout << p[i] << " ";
            cout << endl;    
        }
};

int main()
{
    A obj ;
    obj.setData();
    obj.printData();

    A soj(std::move(obj));
    soj.printData();

}

Valgrind检测错误输出 #

==1198431== Conditional jump or move depends on uninitialised value(s)
==1198431==    at 0x1093BC: A::A(A&&) (in /home/pankaj/practice/PracticeC++Advanced/a.out)
==1198431==    by 0x109233: main (in /home/alex/practice/PracticeC++Advanced/a.out)
==1198431==  Uninitialised value was created by a stack allocation
==1198431==    at 0x1091DA: main (in /home/alex/practice/PracticeC++Advanced/a.out)

错误原因与修复方案 #

错误原因 #

移动构造函数中，刚构造的新对象成员p是未初始化的随机值，此时执行delete [] p会尝试释放一块不确定的内存，这就是Valgrind报错的根源。

修复方法 #

删除移动构造函数中多余的delete [] p语句，直接接管源对象的指针即可——新对象的p还未指向任何有效内存，不需要释放。

修改后的移动构造函数：

A(A&& obj){
    cout << "Move Constructor" << endl;
    p = obj.p;
    obj.p = nullptr;
}

补充说明：移动赋值运算符中的delete [] p是合理的，因为赋值操作针对的是已经完成初始化的对象，p此时指向有效的堆内存，需要先释放再接管源对象的资源。

内容的提问来源于stack exchange，提问作者PANKAJ LADE