将结构值传递给函数

Question

#include<stdio.h>

struct classifier
{
    char src_address[15];
    char dst_address[15];
    int src_port;
    int  dst_port;
};

void display(struct classifier *ptr)
{
    printf("\n%s", ptr->src_address );
    printf("\n%s", ptr->dst_address );
    printf("\n%d", ptr->src_port);
    printf("\n%d", ptr->dst_port );
}

main()
{
    int i;
    struct classifier *ptr[4];
    for(i=0;i<2;i++)
    {
        scanf("%s",ptr[i]->src_address);
        scanf("%s",ptr[i]->dst_address);
        scanf("%d",&ptr[i]->src_port);
        scanf("%d",&ptr[i]->dst_port);
        display(ptr[i]);
    }
    return 0;
}

I want to display output in a function. When I enter the data for the first time, I get proper display. When I enter data for the second time, it displays segmentation fault. What is wrong in the code? According to my knowledge, I have declared the pointers properly. Please help.

Answer 1

You need an array of structures like

struct classifier ptr[4];

Answer 2

You have just declared the pointers but they not pointing to anything valid. You need to allocate memory for every struct and store the memory location of the object in the array.

EDIT: This is valid only if you really want to allocate memory dynamically. Else use the method suggested by @ckv

Answer 3

struct classifier *ptr[4];

In the above definition ptr is an array(of size 4) to pointers of type struct classifier. You have not allocated memory for these pointers and the pointer variable ptr[0..3] are pointing to junk

Instead either you should be mallocing memory or using

struct classifier ptr[4];

This will ensure ptr points to valid struct classifier variables allocated on stack

Answer 4

You haven't allocated the memory for struct classifier

You either want this,

struct classifier *ptr = (classifier*)malloc(4)

followed by,

free(ptr);

or

struct classifier ptr[4];