二进制使用Struct数组成员保存结构（C）？

Question

I'm currently working on a program that uses these two structs:

//Struct to hold contact info about a friend
typedef struct
{
    char *firstName, *lastName;
    char *home, *cell;
} Friend;

//Struct to hold a list of friends and keep track of its size.
typedef struct
{
    Friend *listEntries;
    size_t listSize;
} FriendList;

Each of the string members within the Friend struct is dynamically allocated, as is the listEntries array inside FriendList . I'm trying to save a FriendList as a binary record, but when I try to do this using fwrite() and then read it back with fread() , the listEntries array of the FriendList that is read from the file is empty. Is there any way to save a dynamic struct like this?

EDIT: The functions I use to read/write the struct are:

void writeList(FriendList *fl, char* filename)
{
    FILE *fp = fopen(filename, "wb+");

    if(fp != NULL)
    {
        fwrite(fl, sizeof(FriendList), 1, fp);
    }

    fclose(fp);
}

void readList(FriendList *dest, char* filename)
{
    FILE *fp = fopen(filename, "rb");

    if(fp == NULL)
    {
        printf("oops...");
    }
    else
    {
        fread(dest, sizeof(FriendList), 1, fp);
    }

    close(fp);
}

Answer 1

You must save the data the pointers point at, not the pointers themselves. Pointers are meaningless outside your process as it exists at the very moment, so saving a pointer value to disk means nothing.

In general, you cannot do this by using a single fwrite() to dump out a structure, since that will not follow the pointers.

You need to invent an actual external file format to use, and write code to save and load it. I would suggest a text-based format, since most of your data is text. Perhaps CSV ?