问题描述
当我尝试运行我的程序时,它崩溃的开始。问题是我从文件输入,我可以写文件很好。有人可以解释为什么这个代码不工作?
When I try to run my program it crashes right of the start. The problem is my input from file, I can write to the file fine. Can someone explain why this code wouldn't work??
StringList::StringList()
{
pTop=NULL;
pBottom=NULL;
ifstream in;
in.open("read.txt");
StringListNode * pCurrent;
pCurrent = new StringListNode;
pCurrent = pTop;
while(!in.eof()) //reads it till the end of file
{
in >> pCurrent->data;
pCurrent = pCurrent->pNext;
}
in.close();
}
此输出到文件可以正常工作。我以为我会包括它。
This Output to the file works fine. I thought I would just include it.
StringList::~StringList()
{
ofstream out;
out.open("read.txt");
StringListNode * pCurrent;
pCurrent = new StringListNode;
pCurrent = pTop;
while(pCurrent != 0)
{
out << pCurrent->data << endl;
pCurrent = pCurrent->pNext;
}
out.close();
}
推荐答案
pCurrent = pTop;
为什么在这里分配?这使得 pCurrent
空指针。请移除或修复。
pCurrent = pTop;
Why do you assign this here? This makes pCurrent
null pointer. Please remove or fix.
我与您的验证码混淆:
pCurrent = new StringListNode; // Allocate new memory and point at it
pCurrent = pTop; // Make pCurrent point at same thing as pTop
您分配给 pCurrent
两次。 pTop
看起来像一个数据成员,也许你的意思是在构造函数:
You assign to pCurrent
twice. pTop
looks like a data member, perhaps you meant in constructor:
pCurrent = new StringListNode; // Allocate new memory and point at it
pCurrent->pNext = nullptr; // Assign null to next pointer
pTop = pCurrent; // Make pTop point at new memory
并在析构函数中删除 pCurrent = new
and in destructor remove pCurrent = new StringListNode;
because it does not do anything.
输出时,检查 pCurrent!= 0
,但是在阅读时不检查null。可能 pCurrent
是空指针。
When outputting, you check pCurrent != 0
, but you do not check for null when reading. Probably pCurrent
is null pointer.
另请参阅为什么iostream :: eof在循环条件内被认为是错误?您的回圈应为:
Also, please read Why is iostream::eof inside a loop condition considered wrong?. Your loop should be:
while(pCurrent && (in >> pCurrent->data))
{
pCurrent = pCurrent->pNext;
}
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