在声明中迭代没有大小的结构数组

Question

I've been having problems with trying to iterate over array of structs. The setup is as following:

data.h

typedef struct data {
    char *name;
    char *age;
} data;
data array_of_data[];

data.c

data array_of_data[4] = {
    {"John", "24"},
    {"Melissa", "32"},
    {"Ludwing", "98"}
};

main.c

#include "data.h"
int main() {
    int i=0;
    while(&array_of_data[i] != NULL) {
        do_something();
        i++;
    }
    return 0;    
}

I can't have number of elements in declaration in.h file. So iterating with for loop and sizeof, or while loop doesn't work. With my solution I'm getting an 'undefined reference' error. I don't understand why. Any help is appreciated.

Answer 1

One of the simplest ways to process an array without giving its length is to use a guard value, for example NULL as last value.

This would result in code like this:

data array_of_data[4] = {
    {"John", "24"},
    {"Melissa", "32"},
    {"Ludwing", "98"},
    {NULL, NULL},
};

int main() {
    int i=0;
    while(array_of_data[i].name != NULL) {
        printf("[%d] %s, %s\n", i, array_of_data[i].name, array_of_data[i].age);
        i++;    
    }
}