c - 正在重新分配的指针未分配

Question

实际上这是一个纯 C 程序。当我用 Xcode 编译时。错误 消息说“未分配正在重新分配的指针”

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int LocateElem(int *p1,int e,int leng1);
void Display(int max, int array[]);
int GetElem(int * p, int pass);
int Union(int *p1,int *p2, int leng1, int leng2);
int ListInsert(int *p, int e, int lengA);
int* GetData(int* pArray, int Array_size);
void Show(int *p, int leng);

void InitList_Sq(int  *L);
int *p_A,*p_B;
int m,n;

int main()
{
    clock_t begin, end;
    double  cost;
    begin = clock();


    printf("How many elements of A u want:");
    scanf("%d",&m);
    if (m<0) {
        printf("Error!");
        return 0;
    }
    printf("How many elements of B u want:");
    scanf("%d",&n);
    if (n<0) {
        printf("Error!");
        return 0;
    }

    p_A=(int *)malloc(m*sizeof(int));
    p_B=(int *)malloc(n*sizeof(int));
    if (p_A==NULL) {
        printf("Error allocating memory!\n"); //print an error message
        return 0; //return with failure
    }
    if (p_B==NULL) {
        printf("Error allocating memory!\n"); //print an error message
        return 0; //return with failure
    }

    int *pLast_A, * pLast_B;
    printf("Array A is :\n");
    pLast_A=GetData(p_A, m);
    printf("\nArray B is :\n");
    pLast_B=GetData(p_B, n);

    int newLeng;
    newLeng=Union(p_A,p_B,m,n);

    printf("\nThe Union set is :\n");
    Show(p_A, newLeng);

    free(p_A);
    free(p_B);
    end = clock();
    cost = (double)(end - begin) / CLOCKS_PER_SEC;
    printf("\n%lf seconds", cost);
    return 1;


}


int* GetData(int* pArray, int Array_size){
    int* pFill= pArray;
    int count;
    srand((unsigned) time(NULL));
    for ( count=0; count< Array_size; count++) {
        *(pFill+count)=rand()%1000;
        printf("%d\t", * (pFill+count));
    }
    return pFill+count;
}


int Union(int *p1,int *p2, int leng1, int leng2){
    for (int count=0; count<leng2; count++) {
        int e=GetElem(p2, count);
        while(LocateElem(p1, e, leng1)==0){
            leng1=ListInsert(p1, e, leng1);
        }
    }
    return leng1; 
}

int GetElem(int *p, int pass){
    return  *(p+pass);
}

int LocateElem(int *p1,int e,int leng1){
    for (int count=0; count<leng1; count++)
        if (e==*(p1+count))
            return 1;
        else
            return 0;

}

int ListInsert(int *p, int e, int lengA){
    lengA+=1;
    int* temp;
    temp=(int*)realloc(p, lengA*sizeof(int));
    if (temp==NULL) {
        printf("Error allocating memory!\n"); //print an error message
        free(temp);
        return 0; //return with failure
    }
    else{
        p=temp;
        *(p+lengA-1)=e;

    }
    return lengA;

}

void Show(int *p, int leng){
    for (int count=0; count<leng; count++) {
        printf("%d\t", *(p+leng));
    }
}

编译后 xcode 在 temp=(int*)realloc(p, lengA*sizeof(int)) 行给出断点，信号为 SIGABRT。

Answer 1

问题在于:

int ListInsert(int *p, int e, int lengA){
    int* temp;
    temp=(int*)realloc(p, lengA*sizeof(int));
    ...
    else {
        p=temp; // <<<<< THIS

p 的新值不会传播回 ListInsert 的调用者。发生这种情况是因为 p 是按值传递的。

您需要将int *p 转换为int **p。