在C函数中修改指针时出现问题 [英] Trouble while modifying a pointer within a C function

问题描述

我正在尝试在C中实现一个喜欢的llist操作.我的方法是在标头C文件中实现所有操作，并将其包含在主文件中以管理链接列表.

Hi I'm trying to implement a liked llist operation in C. My approach is to implement all operation in a header C file, and to include it in a main file to manage linked lists.

这是头文件linkedlist.h，其中包含操作实现

Here is the header file linkedlist.h, containing operations implementations

//Here is my code for the node structure:

struct node {
  struct node * next;
  char cinfo;
};


//Here is a method to do a simple insertion in the begining of the list

 void beginInsertSL(char val, struct node ** root){    
  struct node *p = malloc(sizeof(struct node*));
  p->cinfo = val;

  if(*root == NULL){
    p->next = NULL;
  } else {
    p->next = *root;
  }

  *root = p;
};

//Here is a method to do many insertions

void beginInsertSLN(char *ch, struct node **root){
  root  = malloc(sizeof(struct node**));

  int size, i;

  size = strlen(ch);
  i = 0;

  if(size > 0){
    while(i < size){
      beginInsertSL(ch[i], root);
      printSL(*root);
      i++;
    }
  } else *root = NULL;
}

//And finally a method to print a list, to be able to see 

void printSL(struct node *root){
   struct node *p;

  if(root == NULL) printf("[ ]\n");
  else {
    p = root;

    printf("[ %c", p->cinfo);

    while(p->next != NULL) {p = p->next; printf("->%c", p->cinfo);}

    printf(" ]\n");
  }
}

这是使用这些方法的主要功能

Here is the main function to use those methods

#include "linkedlist.h"
#include <stdio.h>

int main(int argc, char *argv[]){

   // declaring the root of my linkedlist
   struct node **root = NULL;

   if(argc > 0){
     // inserting char in the linked list
     beginInsertSLN(argv[1], root);

     // print the linked list to see the result
     printSL(*root);
   }
}

执行此代码时，我得到以下结果:

When executing this code, I get the following result :

./lltest stackoverflow
[ s ]
[ t->s ]
[ a->t->s ]
[ c->a->t->s ]
[ k->c->a->t->s ]
[ o->k->c->a->t->s ]
[ v->o->k->c->a->t->s ]
[ e->v->o->k->c->a->t->s ]
[ r->e->v->o->k->c->a->t->s ]
[ f->r->e->v->o->k->c->a->t->s ]
[ l->f->r->e->v->o->k->c->a->t->s ]
[ o->l->f->r->e->v->o->k->c->a->t->s ]
[ w->o->l->f->r->e->v->o->k->c->a->t->s ]
Erreur de segmentation (core dumped)

有人可以帮助我了解我在这里缺少什么吗?

Can some one help me to understand what I'm missing here ?

推荐答案

代码中的指针一团糟

尝试以下方法.仅考虑到我没有将程序拆分为模块，而是使用了显式指定的字符串.您可以删除它或取消注释main中的字符串定义以测试程序.

Try the following. Take only into account that I did not split the program into modules and used an explicitly specified string. You may remove it or uncomment the string definition in main for testing the program.

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

//Here is my code for the node structure:
struct node 
{
    struct node *next;
    char cinfo;
};


//Here is a method to do a simple insertion in the begining of the list

void beginInsertSL( struct node **root, char c )
{    
    struct node *p = malloc( sizeof( struct node ) );
    p->cinfo = c;
    p->next = *root;

    *root = p;
}

void printSL( struct node *root );

//Here is a method to do many insertions

void beginInsertSLN( struct node **root, const char *s  )
{
    while ( *s )
    {
        beginInsertSL( root, *s++ );
        printSL( *root );
    }
}

//Here is a method to print a list, to be able to see 

void printSL( struct node *root )
{
    if ( root == NULL ) 
    {
        printf( "[ ]\n" );
        return;
    }

    printf( "[ %c", root->cinfo );

    while( ( root = root->next ) != NULL ) 
    {
        printf( "->%c", root->cinfo );
    }

    printf(" ]\n");
}

//And finally a method to clear the list 

void clear( struct node **root )
{
    while ( *root )
    {
        struct node *tmp = *root;
        *root = ( *root )->next;
        free( tmp );
    }
}    

int main( int argc, char * argv[] )
{
    struct node *root = NULL;

    if ( argc > 1 ) beginInsertSLN( &root, argv[1] );

//    char *s = "stackoverflow";
//    beginInsertSLN( &root, s );

    printSL( root );

    clear( &root );

    return 0;
}

输出为

[ s ]
[ t->s ]
[ a->t->s ]
[ c->a->t->s ]
[ k->c->a->t->s ]
[ o->k->c->a->t->s ]
[ v->o->k->c->a->t->s ]
[ e->v->o->k->c->a->t->s ]
[ r->e->v->o->k->c->a->t->s ]
[ f->r->e->v->o->k->c->a->t->s ]
[ l->f->r->e->v->o->k->c->a->t->s ]
[ o->l->f->r->e->v->o->k->c->a->t->s ]
[ w->o->l->f->r->e->v->o->k->c->a->t->s ]
[ w->o->l->f->r->e->v->o->k->c->a->t->s ]

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