第二个问题我询问同一个程序。感觉不对,但无法提供帮助。while循环之外的变量在重新分配时变为NULL
这里是导致该问题的代码:
int main()
{
Link* link = new Link();
Instance* A = new Instance('A');
Instance* B = new Instance('B');
Instance* C = new Instance('C');
Instance* D = new Instance('D');
Instance* E = new Instance('E');
Instance* F = new Instance('F');
Instance* G = new Instance('G');
Instance* H = new Instance('H');
Instance* I = new Instance('I');
Instance* J = new Instance('J');
Instance* K = new Instance('K');
Instance* L = new Instance('L');
Instance* current= new Instance('X');
A->setNearbyObjects(NULL,B,E,NULL);
B->setNearbyObjects(NULL,NULL,F,A);
C->setNearbyObjects(NULL,D,G,NULL);
D->setNearbyObjects(NULL,NULL,NULL,C);
E->setNearbyObjects(A,NULL,I,NULL);
F->setNearbyObjects(B,G,NULL,NULL);
G->setNearbyObjects(C,H,K,F);
H->setNearbyObjects(NULL,NULL,L,G);
I->setNearbyObjects(E,J,NULL,NULL);
J->setNearbyObjects(NULL,NULL,NULL,I);
K->setNearbyObjects(G,NULL,NULL,NULL);
L->setNearbyObjects(H,NULL,NULL,NULL);
string nesw[4] = {"(N)orth","(E)ast","(S)outh","(W)est"};
char choice='X';
current=A;
while((current!=L)&&(choice!='Q'))
{
current->message();
cout<<"You can go ";
for(int i=0;i<current->getPaths().size();i++)
{
if(current->getPaths()[i]!=NULL)
{
cout<<nesw[i].c_str()<<", ";
}
}
cout<<"or (Q)uit"<<endl;
cin>>choice;
choice=toupper(choice);
while((choice!='N')&&(choice!='E')&&(choice!='S')&&(choice!='W')&&(choice!='Q'))
{
cout<<"Choice: "<<choice<<endl;
cout<<"Invalid input. Try again..."<<endl;
cin>>choice;
choice=toupper(choice);
}
switch(choice)
{
case 'N':
current=current->getPaths()[0];
case 'E':
current=current->getPaths()[1];
case 'S':
current=current->getPaths()[2];
case 'W':
current=current->getPaths()[3];
default:
break;
}
}
if(current==L)
{
cout<<"\n\nYou have found the exit."<<endl;
}
return 0;
};
这个“当前”变量存储当前对象,你会觉得。我在开始while循环之前将它设置为对象A。在while循环结束时,我通过case语句将其更改为其他内容。
问题是,当循环返回到开始时,'current'变为NULL。当我尝试调用current-> message()时,它会翻倒,因为'current'内没有任何内容。
感觉就像我在这里做的一些基本错误。但是我已经在这个问题上抨击了我2天,而且没有任何效果。
任何人都可以给我一个解释,这里发生了什么?
您可以在'current = current-> getPaths()[0];等表达式中重新赋值'current';''current''取决于'current- > getPaths()[0]' – SomeWittyUsername
是的。而且我在赋值时检查了它,getPaths()[0]不是空的,'当前'肯定被赋值为getPaths()[x]的值。 – eltaro
这些'cout << nesw [i] .c_str()<<“,”;'语句的输出是什么?你会得到全部4个,就像你期待的那样? – Tushar