gistfile1.c

#include <stdio.h>

struct json_field {
    const char* field;
    int is_here;
};

int main(void)
{
    /* Met 0 ou 1 pour simuler l'absence/présence du champ */
    struct json_field fields[] = { { "'fsname': 'dev'", 1 },
                                   { "'percentage_used': '0.000000'", 1 },
                                   { "'mount_point': 'dev/'", 1 } };
    size_t i;

    printf("{");
    const char *comma = "";
    for (i = 0; i < (sizeof fields/sizeof fields[0]); ++i) {
        if (fields[i].is_here) {
            printf("%s\n\t%s", comma, fields[i].field);
            comma = ",";
        }
    }
    puts("\n}");
    return 0;
}