C - How to initialise array of structures when the array size is large? [duplicate]

Question

Say I have a structure:

struct foo{
    int field_1;
    int field_2;
};

And say have an array:

foo bar[1000];

I understand that you can initialise arrays like this:

foo bar[]={
{ .field_1= 10, field_2 = 20 },
{ .field_1= 30, field_2 = 40 },
};

This is not practical at all when the array has 1000 elements. I need to initialise all elements to a specific integer (at compile time) but it looks like it is not practically possible to do this unless the array is very small. It seems like an essential thing to be able to do but I can't find a solution.

Thanks.

Answer 1

You can initialize a struct using a for loop like this -

#include<stdio.h>

struct foo{
        int field_1;
        int field_2;
    };

int main(){

    int i;
    struct foo bar[1000];

    for(i=0; i<1000; i++){
        bar[i].field_1 = i;
        bar[i].field_2 = 2*i;
    }

    for(i=0; i<1000; i++){
       printf("bar[%d]:: field_1: %d field_2: %d\n", i, bar[i].field_1, bar[i].field_2);
    }
    return 0;
}

Answer 2

You can simply create a special "generator" program, which outputs desired C source code for an array with 1000+ initialized elements.

Answer 3

Run a script in your favorite language (e.g., Python), which writes this array into a header file:

fileDesc = open('MyArray.h','wt')
fileDesc.write('#define MY_ARRAY \\\n{ \\\n')
for n in range(0,1000):
    fileDesc.write('\t{.field_1 = ' + '%5d'%(10+20*n) +
                   ' , .field_2 = ' + '%5d'%(20+20*n) + '}, \\\n')
fileDesc.write('}\n')
fileDesc.close()

Then, in the source file, simply include the auto-generated header file and initialize the array:

#include "MyArray.h"
...
foo bar[] = MY_ARRAY;