在C中完成链接列表时出现问题＃

Question

我的代码几乎完成了一个疯狂的错误！当我终止最后一个节点来完成链接列表时，它实际上会转储所有链接并使第一个节点链接为空！ 当我追踪它时，它的工作完全正常，在循环中创建列表，但在循环完成后会发生，并且通过这样做破坏链接的其余部分，我不明白为什么某些显而易见的问题变得有问题！ （最后一行）

struct poly { public int coef; public int pow; public poly* link;} ; 
     poly* start ; 
     poly* start2; 
     poly* p; 
     poly* second; 
     poly* result; 
     poly* ptr; 
     poly* start3; 
     poly* q; 
     poly* q2; 
     private void button1_Click(object sender, EventArgs e) 
     { 
      string holder = ""; 
      IntPtr newP = Marshal.AllocHGlobal(sizeof(poly)); 
      q = (poly*)newP.ToPointer(); 
      start = q; 
      int i = 0; 
      while (this.textBox1.Text[i] != ',') 
      { 
       holder += this.textBox1.Text[i]; 
       i++; 
      } 
      q->coef = int.Parse(holder); 
      i++; 
      holder = ""; 
      while (this.textBox1.Text[i] != ';') 
      { 
       holder += this.textBox1.Text[i]; 
       i++; 
      } 
      q->pow = int.Parse(holder); 
      holder = ""; 
      p = start; 
      //creation of the first node finished! 
      i++; 
      for (; i < this.textBox1.Text.Length; i++) 
      { 
       newP = Marshal.AllocHGlobal(sizeof(poly)); 
       poly* test = (poly*)newP.ToPointer(); 
       while (this.textBox1.Text[i] != ',') 
       { 
        holder += this.textBox1.Text[i]; 
        i++; 
       } 
       test->coef = int.Parse(holder); 
       holder = ""; 
       i++; 

       while (this.textBox1.Text[i] != ';' && i < this.textBox1.Text.Length - 1) 
       { 
        holder += this.textBox1.Text[i]; 
        if (i < this.textBox1.Text.Length - 1) 
         i++; 
       } 
       test->pow = int.Parse(holder); 
       holder = ""; 
       p->link = test; //the addresses are correct and the list is complete 
      } 
      p->link = null;  //only the first node exists now with a null link! 
} 

Answer 1

p始终保持对第一个元素的引用，所以是的，p->link = null;完全符合您所说的内容。在我看来，你想是这样的：

... 
    p->link = test; 
    p = test; 
    .... 

编辑：

概念证明

public unsafe struct poly { public int coef; public int pow; public poly* link; } 

public unsafe class Program 
{ 
    static void Main(string[] args) 
    {    
     poly* temp1, temp2, start = 
      (poly*)Marshal.AllocHGlobal(sizeof(poly)).ToPointer(); 
     start->coef = 0; 
     start->pow = 0; 
     temp1 = start; 
     for (int i = 1; i < 10; i++) 
     { 
      temp2 = (poly*)Marshal.AllocHGlobal(sizeof(poly)).ToPointer(); 
      temp2->coef = i; 
      temp2->pow = i; 
      temp1->link = temp2; 
      temp1 = temp2; 
     } 
     temp1->link = null; 
     temp1 = start; 

     while (temp1 != null) 
     { 
      Console.WriteLine(
       string.Format(
        "eoef:{0}, pow:{1}", 
        temp1->coef, 
        temp1->pow)); 
      temp1 = temp1->link; 
     } 
    } 
} 

Answer 2

我认真地建议你退后一步，清理你的代码。从基本的一瞥来看，它似乎没有对你写的代码量做太多的事情。注意只有结束条件不同的重复代码块。他们是方法的主要候选人。重构几分钟后，您可能会删除一半的代码，并清楚地了解您正在尝试完成的任务并轻松找到错误。

Answer 3

编辑：struct没有不安全的指针链表...在最奇怪的要求上课。

public struct Polynomial 
{ 
    public int Coefficient; 
    public int Power; 
    public Polynomial? Link; 
} 

private Polynomial? start; 

private void button1_Click(object sender, EventArgs e) 
{ 
    string holder = String.Empty; 
    start = new Polynomial(); 
    int i = 0; 
    while (this.textBox1.Text[i] != ',') 
    { 
     holder += this.textBox1.Text[i]; 
     i++; 
    } 

    start.Value.Coefficient = Int32.Parse(holder); 

    i++; 
    holder = String.Empty; 
    while (this.textBox1.Text[i] != ';') 
    { 
     holder += this.textBox1.Text[i]; 
     i++; 
    } 

    start.Value.Power = Int32.Parse(holder); 
    Polynomial? p = start; 

    //creation of the first node finished! 
    i++; 
    for (; i < this.textBox1.Text.Length; i++) 
    { 
     Polynomial? test = new Polynomial(); 

     holder = String.Empty; 
     while (this.textBox1.Text[i] != ',') 
     { 
      holder += this.textBox1.Text[i]; 
      i++; 
     } 

     test.Value.Coefficient = Int32.Parse(holder); 

     i++; 
     holder = String.Empty; 
     while (this.textBox1.Text[i] != ';' && i < this.textBox1.Text.Length - 1) 
     { 
      holder += this.textBox1.Text[i]; 
      if (i < this.textBox1.Text.Length - 1) 
       i++; 
     } 

     test.Value.Power = Int32.Parse(holder); 
     p.Value.Link = test; //the addresses are correct and the list is complete 
     p = test; 
    } 
}