訪問字段會導致取消引用 C 中的 null 指針

Question

這個問題與 C Programming Language: I get error: Access to field 'x' results in a dereference of null pointer 有關

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

typedef struct A {  
    int *x;  
    int *y;  
} A;  

void allocateStruct(int sizeN, A *aType);
void printInfo(A *aType);
  
int main() {   
    A *genericA;  
    allocateStruct(5, genericA);  
    int x[5] = {2, 3, 4, 5, 6};  
    int y[5] = {12, 36, 40, 52, 23};   

    genericA->x = x;  
    genericA->y = y;  
    printInfo(genericA);   
}  

void allocateStruct(int sizeN, A* aType) {  
    aType->x = (int*)malloc(sizeN * sizeof(int));   
    aType->y = (int*)malloc(sizeN * sizeof(int));    
}  
 
void printInfo(A *aType) { 
    printf("%i %i\n",  aType->x[0], aType->y[0] ); 
} 

Answer 1

您尚未將 memory 分配給該結構，但您正在訪問它的成員

void allocateStruct(int sizeN, A* aType) {
    aType->x = (int*)malloc(sizeN * sizeof(int));   
    aType->y = (int*)malloc(sizeN * sizeof(int));    
}

先將 memory 分配給結構體本身

atype = malloc(sizeof(A))