Correct way to hard code command line arguments

Question

Following code basiaclly lets access to GPIO port with LED.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
int main(int argc, char *argv[])
{
    extern char *optarg;
    char *cptr;
    int gpio_value = 0;
    int nchannel = 0;

    int c;
    int i;

    opterr = 0;

    while ((c = getopt(argc, argv, "g:io:ck")) != -1) {
        switch (c) {
            case 'g':
                gl_gpio_base = (int)strtoul(optarg, &cptr, 0);
                if (cptr == optarg)
                    usage(argv[0]);
                break;
            case 'i':
                gpio_opt = IN;
                break;
            case 'o':
                gpio_opt = OUT;
                gpio_value = (int)strtoul(optarg, &cptr, 0);
                if (cptr == optarg)
                    usage(argv[0]);
                break;
            case 'c':
                gpio_opt = CYLON;
                break;
            case 'k':
                gpio_opt = KIT;
                break;
            case '?':
                usage(argv[0]);
            default:
                usage(argv[0]);

        }
    }

    if (gl_gpio_base == 0) {
        usage(argv[0]);
    }

    nchannel = open_gpio_channel(gl_gpio_base);
    signal(SIGTERM, signal_handler); /* catch kill signal */
    signal(SIGHUP, signal_handler); /* catch hang up signal */
    signal(SIGQUIT, signal_handler); /* catch quit signal */
    signal(SIGINT, signal_handler); /* catch a CTRL-c signal */
    switch (gpio_opt) {
        case IN:
            set_gpio_direction(gl_gpio_base, nchannel, "in");
            gpio_value=get_gpio_value(gl_gpio_base, nchannel);
            fprintf(stdout,"0x%08X\n", gpio_value);
            break;
        case OUT:
            set_gpio_direction(gl_gpio_base, nchannel, "out");
            set_gpio_value(gl_gpio_base, nchannel, gpio_value);
            break;
        case CYLON:
#define CYLON_DELAY_USECS (10000)
            set_gpio_direction(gl_gpio_base, nchannel, "out");
            for (;;) {
                for(i=0; i < ARRAY_SIZE(cylon); i++) {
                    gpio_value=(int)cylon[i];
                    set_gpio_value(gl_gpio_base, nchannel, gpio_value);
                }
                usleep(CYLON_DELAY_USECS);
            }
        case KIT:
#define KIT_DELAY_USECS (10000)
            set_gpio_direction(gl_gpio_base, nchannel, "out");
            for (;;) {
                for (i=0; i<ARRAY_SIZE(kit); i++) {
                    gpio_value=(int)kit[i];
                    set_gpio_value(gl_gpio_base, nchannel, gpio_value);
                }
                usleep(KIT_DELAY_USECS);
            }
        default:
            break;
    }
    close_gpio_channel(gl_gpio_base);
    return 0;
}

Genarlly I would give commands like this;

gpio-demo -g 255 -o 0

255 above tells me chip number, 000 tells me what data will go to GPIO port.

This would turn off all the LEDs.

However for some debugging purpose I have to modify this code such that it behaves a litlle differently:

When running teh program, tt should simply switch off the LED i.e run the following command.

gpio-demo -g 255 -o 0

This is the only command that will work- hard coded. An ON LED will be now OFF.

What I tried is I inserted the command as the first line in main:

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


argv = "gpio-demo -g 255 -o 0"  //irrespective of what user what user type, run this command. gpio-demo is the binary of this program 
.
.
.
.

    }

is this the correct way to hard code command line arguments ?

Answer 1

If you call you program like this gpio-demo -g 255 -o 0, than argc would be equal to 5 and argv will be a list of five pointers to sequences of characters where the first is gpio-demo, the second -g, the third 255, ...

So if you really want to hardcode, you would have to write:

argc = 5;
argv = (char**)malloc(sizeof(char*)*argc);
argv[0] = "gpio-demo";
argv[1] = "-g";
argv[2] = "255";
argv[3] = "-o";
argv[4] = "0";

However, I would not recommend this! Rather use a bash script with the desired command line.