Thread: Is there a way to point to one structure array entry from another at compile time?

Here's the scenario.

I have some structures...

Code:

struct entry { 
     char name[8] ;   
     int  age  ;  
} ; 

struct entry Table1[] = {     // An array of entry's. 
     "Dino"   , 1 , 
     "Bambam" , 2 , 
     "Pebbles", 3 
} ;  

struct section { 
     struct entry * an_entry ;  
     int  length ;  
     char data[8] ;  
} 

// I'm struggling with the structure below... 

struct section Table2[] = {   // An array of sections 
    & first entry in Table1  , 5, "abc" ,  
    & second entry in Table1 , 5, "def" ,  
    & third entry in Table1  , 2, "9999"  
} ;

Conceptually, I would like to be able to assign a label to each entry of Table1 so that Table2 section.an_entry points to the Table1 entry I want. It's a constant table and does not change at runtime.

This, obviously isn't legal syntax, but it would look like this

Code:

 
struct entry Table1[] = {     // An array of entry's. 
e1:    "Dino"   , 1 , 
e2:    "Bambam" , 2 , 
e3:    "Pebbles", 3 
} ;  

struct section Table2[] = {   // An array of sections 
    &e1 , 5, "abc" ,  
    &e2 , 5, "def" ,  
    &e3 , 2, "9999"  
} ;

Is there a way to do this? I haven't tried to see if it's legal, but if it is, I would rather not code

Code:

 
struct section Table2[] = {   // An array of sections 
    &Table1[0] , 5, "abc" ,  
    &Table2[1] , 5, "def" ,  
    &Table1[2] , 2, "9999"  
} ;

because Table1 might change in the future, and it might have 50 elements in it. I would prefer a symbolic label or address instead of hardcoding an array subscript (again, if it's even legal).

So long as your compiler is at least C99, you can use designated initialisers.

Code:

#include <stdio.h>
#include <string.h>

enum {
    E_DINO,
    E_BAMBAM,
    E_PEBBLES,
};

struct entry { 
     char name[8] ;   
     int  age  ;  
} ; 
 
struct entry Table1[] = {     // An array of entry's. 
     [E_DINO] = { "Dino"   , 1 }, 
     [E_BAMBAM] = { "Bambam" , 2 }, 
     [E_PEBBLES] = { "Pebbles", 3 }
} ;  
 
struct section { 
     struct entry * an_entry ;  
     int  length ;  
     char data[8] ;  
} ;
 
// I'm struggling with the structure below... 
 
struct section Table2[] = {   // An array of sections 
    { &Table1[E_DINO], 5, "abc" },  
    { &Table1[E_BAMBAM], 5, "def" },  
    { &Table1[E_PEBBLES], 2, "9999"}
} ;

int main ( ) {
    printf("%s\n", Table2[1].an_entry->name);
    return 0;
}

Works perfect! Great solution. Thank you!