c - 将双指针传递给另一个函数

Question

我正在努力解决如何传递指针以便能够根据主函数中的头搜索链表。它是一个包含多项式系数和指数的结构。在 allocateTerm 函数中，我尝试将双指针传递给另一个函数来搜索并查看我要创建的项是否已在多项式中具有公共(public)项。代码如下:

typedef struct PolyTerm{
  int iCoeff;
  int iExp;
  struct PolyTerm *pNext;
}PolyTerm;

PolyTerm *allocateTerm(int iCoeff, int iExp, PolyTerm **ppHead, PolyTerm *pCurr);
PolyTerm *findTerm(int iCoeff, int iExp, PolyTerm ***ppHead);

void main(int argc, char *argv[])
{
  PolyTerm *pPolyAHead = NULL;
  PolyTerm *pCurr = NULL;

  allocateTerm(2,3,&pPolyAHead, pCurr);
  pCurr = allocateTerm(3,4,&pPolyAHead, pCurr);
  pCurr = allocateTerm(4,5,&pPolyAHead, pCurr);
  pCurr = allocateTerm(5,6,&pPolyAHead, pCurr);

  printf("%p\n", pPolyAHead);

  for(pCurr = pPolyAHead; pCurr != NULL; pCurr=pCurr->pNext)
    printf("coeff: %d exp: %d address: %p\n", pCurr->iCoeff, pCurr->iExp, pCurr);

  PolyTerm *pPolyBHead = NULL;

  allocateTerm(7,8,&pPolyBHead, pCurr);
  pCurr = allocateTerm(9,10,&pPolyBHead, pCurr);
  pCurr = allocateTerm(11,12,&pPolyBHead, pCurr);
  pCurr = allocateTerm(13,14,&pPolyBHead, pCurr);

  for(pCurr = pPolyBHead; pCurr != NULL; pCurr=pCurr->pNext)
    printf("coeff: %d exp: %d address: %p\n", pCurr->iCoeff, pCurr->iExp, pCurr);

}

PolyTerm *allocateTerm(int iCoeff, int iExp, PolyTerm **ppHead, PolyTerm *pCurr)
{
  PolyTerm *pFind = NULL;
  if(*ppHead == NULL)
    {
      *ppHead = (PolyTerm *)malloc(sizeof(PolyTerm));
      if(*ppHead == NULL)
    {
      printf("Memory allocation error with ppHead\n");
    }
      (*ppHead)->iCoeff = iCoeff;
      (*ppHead)->iExp = iExp;
      (*ppHead)->pNext = NULL;
    }
  else
    {
      // Search to see if that exponent already exists
      printf("%p\n", *ppHead);
      pFind = findTerm(iCoeff, iExp, /*????? (some form of **pHead)*/);
      if(pFind == NULL)
    {
      PolyTerm *pNew = NULL;
      pNew = (PolyTerm *)malloc(sizeof(PolyTerm));
      if(pNew == NULL)
        printf("Memory allocation error with pNew\n");
      if((*ppHead)->pNext == NULL)
        {
          (*ppHead)->pNext = pNew;
        }
      else
        {
          pCurr->pNext = pNew;
        }
      pNew->iCoeff = iCoeff;
      pNew->iExp = iExp;
      pNew->pNext = NULL;
    }
      else
    {
      pFind->iCoeff += iCoeff;
    }
    }
}

PolyTerm *findTerm(int iCoeff, int iExp, PolyTerm ?????/*????? (some form of **pHead)*/)
{
  //printf("%p", &head);
  /*
  PolyTerm *pFind = NULL;
  for(pFind = (*ppHead); pFind != NULL; pFind = (*ppHead)->pNext)
    {
      if(pFind->iExp == iExp)
    return pFind;
    }
    return NULL;*/
}

Answer 1

我对你的函数做了一些修改，我不确定到底是哪些修改，但大部分原始语法都完好无损。我相信下面的代码能够实现您所追求的目标。如有遗漏请留言。

#include<stdlib.h>
#include<stdio.h>

typedef struct PolyTerm{
  int iCoeff;
  int iExp;
  struct PolyTerm *pNext;
}PolyTerm;

PolyTerm *allocateTerm(int iCoeff, int iExp, PolyTerm **ppHead, PolyTerm *pCurr);
PolyTerm *findTerm(int iCoeff, int iExp, PolyTerm **ppHead);

void main(int argc, char *argv[])
{
    setbuf(stdout, NULL);

    PolyTerm *pPolyAHead = NULL;
    PolyTerm *pCurr = NULL;

    pCurr = allocateTerm(2,3,&pPolyAHead, pCurr);
    //printf("%d %d %p %p\n",pCurr->iCoeff,pCurr->iExp,pPolyAHead,pCurr->pNext);
    pCurr = allocateTerm(3,4,&pPolyAHead, pCurr);
    //printf("%d %d %p\n",pCurr->iCoeff,pCurr->iExp,pCurr->pNext);
    pCurr = allocateTerm(4,5,&pPolyAHead, pCurr);
    pCurr = allocateTerm(5,6,&pPolyAHead, pCurr);

    //printf("main: %p\n", pPolyAHead);

    for(pCurr = pPolyAHead; pCurr != NULL; pCurr=pCurr->pNext)
        printf("coeff: %d exp: %d address: %p\n", pCurr->iCoeff, pCurr->iExp, pCurr);

    //exit(1);

    PolyTerm *pPolyBHead = NULL;

    allocateTerm(7,8,&pPolyBHead, pCurr);
    pCurr = allocateTerm(9,10,&pPolyBHead, pCurr);
    pCurr = allocateTerm(11,12,&pPolyBHead, pCurr);
    pCurr = allocateTerm(13,14,&pPolyBHead, pCurr);

    for(pCurr = pPolyBHead; pCurr != NULL; pCurr=pCurr->pNext)
    printf("coeff: %d exp: %d address: %p\n", pCurr->iCoeff, pCurr->iExp, pCurr);

}

PolyTerm *allocateTerm(int iCoeff, int iExp, PolyTerm **ppHead, PolyTerm *pCurr)
{
    PolyTerm *pFind = NULL;
    if(*ppHead == NULL) {
        // Occurs only on first entry.
        *ppHead = (PolyTerm *)malloc(sizeof(PolyTerm));
        if(*ppHead == NULL)
            printf("Memory allocation error with ppHead\n");

        (*ppHead)->iCoeff = iCoeff;
        (*ppHead)->iExp = iExp;
        (*ppHead)->pNext = NULL;
        return *ppHead;
    } else {
        // Search to see if that exponent already exists
        //printf("allocate: %p\n", *ppHead);
        pFind = findTerm(iCoeff, iExp, ppHead);
        if(pFind == NULL) {
            PolyTerm *pNew = NULL;
            pNew = (PolyTerm *)malloc(sizeof(PolyTerm));
            if(pNew == NULL)
                printf("Memory allocation error with pNew\n");

            if((*ppHead)->pNext == NULL)
                (*ppHead)->pNext = pNew;
            else
                pCurr->pNext = pNew;

            pNew->iCoeff = iCoeff;
            pNew->iExp = iExp;
            pNew->pNext = NULL;
        } else {
            pFind->iCoeff += iCoeff;
        }
    }
}

PolyTerm *findTerm(int iCoeff, int iExp, PolyTerm **ppHead)
{
    //printf("find: %p\n", *ppHead);

    PolyTerm *pFind;
    for(pFind = *ppHead; pFind->pNext != NULL; pFind = pFind->pNext) {
        //printf("find: iExp %d %d\n",pFind->iExp, iExp);
        if(pFind->iExp == iExp) {
            //printf("find: returned\n");
            return pFind;
        }
    }
    //printf("find: not found\n");
    return NULL;
}

输出:

coeff: 2 exp: 3 address: 001B1C28
coeff: 3 exp: 4 address: 001B1C40
coeff: 4 exp: 5 address: 001B1C58
coeff: 5 exp: 6 address: 001B1C70
coeff: 7 exp: 8 address: 001B1668
coeff: 9 exp: 10 address: 001B1680
coeff: 11 exp: 12 address: 001B1698
coeff: 13 exp: 14 address: 001B16B0