c - 为什么根节点值无效？

Question

我想创建一棵回归树。为什么生成树后无法从根节点获取有效值？

/* 
 * File:   main.c
 * Author: C-AP
 *
 * Created on September 9, 2011, 8:06 PM
 */
#include <stdio.h>
#include <stdlib.h>

typedef struct regnode {
    int setsize;
    int* set;
    int tokenpos;
    int nextsize;
    struct regnode** next;
} regnode;

/*
 * print array
 */
void printliniar2(int dim, int* mat, char* label) {
    int i;
    printf("\n%s\n", label);
    for (i = 0; i < dim; i++)
        printf(" %d ,", mat[i]);
    printf("\n");
}

/*
 * copies array source to array destination
 */
void copyToInt(int dim, int* Source, int* Destination) {
    int i;
    for (i = 0; i < dim; i++)
        Destination[i] = Source[i];
}

void getReducedSet(int dim, int* set, int delpos, int* newset){
    int i,j=0;
    for(i=0;i<delpos;i++,j++)
        newset[j] = set[i];
    for(i=delpos+1;i<dim;i++,j++)
        newset[j] = set[i];

}

void genTree(int setsize, int* set, int tokenpos, regnode* node){

    printf("\n**********************************\n");

    //allocate memory for node variable
    node = (regnode*)malloc(sizeof(regnode));

    //insert set dimension
    node->setsize = setsize;
    printf("node setsize : %d",node->setsize);

    //allocate set space
    node->set = calloc(node->setsize,sizeof(int));

    //insert set into node    
    copyToInt(setsize,set,node->set);
    printliniar2(node->setsize,node->set,"node set (copy)");

    //insert token position
    node->tokenpos = tokenpos;
    printf("\nnode tokenpos : %d\n",node->tokenpos);

    //insert number of next nodes
    node->nextsize = setsize - 1 - tokenpos;
    printf("\nnode nextsize : %d\n",node->nextsize);

    //allocate memory for next nodes
    node->next = malloc(node->nextsize*sizeof(regnode*));

    //create children nodes
    int i;
    for(i=0;i<node->nextsize;i++){
        //create next node
        regnode* next;

        //get reduced set for child node
        int* newset = calloc(setsize-1,sizeof(int));
        getReducedSet(setsize,set,tokenpos+i,newset);

        //keep reference to next node
        node->next[i] = next;

        //recursively call genTree
        genTree(setsize-1,newset,tokenpos+i,next);
    }
}

/*
   void exploreTree(regnode* root){
   printf("\n**********************************\n");
   printf("\nnode setsize : %d\n",root->setsize);
   printliniar2(root->setsize,root->set,"set");
   printf("\nNumber of next nodes : %d\n",root->nextsize);
   int i;
   for(i=0;i<root->nextsize;i++)
   exploreTree(root->next[i]);
   }
   */

/*
 * 
 */
int main(int argc, char** argv) {
    int dim = 5;
    int set[] = {1,2,3,4,5};
    int tokenpos=0;
    regnode* root;

    genTree(dim,set,tokenpos,root);
    //exploreTree(root);

    printf("\nSet dimension : %d\n",root->setsize);
    printliniar2(root->setsize,root->set,"set");
    printf("\nNumber of next nodes : %d\n",root->nextsize);

    return (EXIT_SUCCESS);
}

Answer 1

root 按值传递，genTree 永远不会返回创建的节点。