Save an integer array written in C to a JSON text file array

Question

How would one go about saving an integer array written as a c file into a JSON text file array file? Any help or links would be greatly appreciated.

Answer 1

Continuing from the comment. When you declare an array, such as:

int array[] = { 1, 2, 3, 4, 5, 6, 7, 8 };

That array exists in memory and you can pass the array to your output function that will write the array to a file in the format you specify. When you pass an array to a function you also need to pass the size of the array. An array variable passed as a parameter to a function is converted to a pointer. Following the conversion, there is no way to determine the size of the original array in the function. (in a general sense)

All you need your function to do is open a file for writing, write any text needed before you write the array elements, write the array elements, then write any closing formatting needed. A quick example to help you along could be something like the following where the array values are written to the filename provided on the command line (or "jsonout.txt" default):

#include <stdio.h>

void jsonout (char *fname, int *a, size_t sz);

int main (int argc, char **argv) {

    int array[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
    size_t size = sizeof array/sizeof *array;
    char *file = argc > 1 ? argv[1] : "jsonout.txt";

    jsonout (file, array, size);

    return 0;
}

/* output function to write "{ "array" : [ v1, v2, .... ] }" to 'fname'
 * where v1, v2, ... are the values in the array 'a' of size 'sz'
 */
void jsonout (char *fname, int *a, size_t sz)
{
    size_t i;
    FILE *fp = fopen (fname, "w+"); /* open file for writing */

    if (!fp) {  /* validate file is open, or throw error */
        fprintf (stderr, "jsonout() error: file open failed '%s'.\n", 
                fname);
        return;
    }

    fprintf (fp, "{ \"array\" : [");    /* print header to file */

    for (i = 0; i < sz; i++)            /* print each integer   */
        if (i == 0)
            fprintf (fp, " %d", a[i]);
        else
            fprintf (fp, ", %d", a[i]);

    fprintf (fp, " ] }\n");     /* print closing tag */

    fclose (fp);
}

Output File

$ cat jsonout.txt
{ "array" : [ 1, 2, 3, 4, 5, 6, 7, 8 ] }

Let me know if you need further help.