Send arguments to a function with argv and argc

Question

Can someone help me to understand how i need to send the parameters to the function "lora_rf_config" ? Thank you so much !

I try with:

char cfgred[7][10]={'lora_rf_config','915000000','10','0','1','8','14'};
lora_rf_config(7,&cfgred);

The function that im trying to use is:

static void lora_rf_config(int argc, char *argv[])
{
    if (argc == 1) {      
        e_printf("OK%d,%d,%d,%d,%d,%d\r\n",  g_lora_config.lorap2p_param.Frequency, 
                                             g_lora_config.lorap2p_param.Spreadfact,
                                             g_lora_config.lorap2p_param.Bandwidth,
                                             g_lora_config.lorap2p_param.Codingrate,
                                             g_lora_config.lorap2p_param.Preamlen,
                                             g_lora_config.lorap2p_param.Powerdbm );
        return;
    } else {
        if (argc != 7) {
            out_error(RAK_ARG_ERR);
            return;
        }
    if (!(CHECK_P2P_FREQ(atoi(argv[1])) &&
             CHECK_P2P_SF(atoi(argv[2])) &&
             CHECK_P2P_BDW(atoi(argv[3])) &&
             CHECK_P2P_CR(atoi(argv[4])) &&
             CHECK_P2P_PREMLEN(atoi(argv[5])) &&
             CHECK_P2P_PWR(atoi(argv[6])))) {
            out_error(RAK_ARG_ERR);
        return;  
      } 

      if (read_partition(PARTITION_0, (char *)&g_lora_config, sizeof(g_lora_config)) < 0) {
          out_error(RAK_RD_CFG_ERR);
          return;
      }

      g_lora_config.lorap2p_param.Frequency = atoi(argv[1]);
      g_lora_config.lorap2p_param.Spreadfact = atoi(argv[2]);
      g_lora_config.lorap2p_param.Bandwidth = atoi(argv[3]);
      g_lora_config.lorap2p_param.Codingrate = atoi(argv[4]);
      g_lora_config.lorap2p_param.Preamlen = atoi(argv[5]);
      g_lora_config.lorap2p_param.Powerdbm = atoi(argv[6]);
      write_partition(PARTITION_0, (char *)&g_lora_config, sizeof(g_lora_config));
      e_printf("OK\r\n");
    }

    return;
}

The error that i got is:

..\..\..\src\application\RAK811\app.c(107): error:  #26: too many characters in character constant
  char cfgred[7][10]={'lora_rf_config','915000000','10','0','1','8','14'};

I dont have experience with this kind of arguments. Thank you for your time.

Answer 1

lora_rf_config expects same arguments than main function: array of pointers to strings, and its length.

Strings in C are pointers to char, where the char buffer they point to has terminating NUL character (if NUL char is missing, then it's not a string, just a character array). In other words, there is no string type in C, but stringiness is determined by the actual data in the char array or buffer. Using "" string literal creates a string, IOW it adds that terminating NUL char in addition to what you write.

// cfgred is array([) of 7 pointers(*) to char.
// Note: string literals are read-only, so you must not modify these
// strings. If you want a modifiable string, this would be a bit more complex,
// but I think this is out of the scope of your question.
char *cfgred[7] = { "lora_rf_config" , "915000000", "10","0", "1", "8", "14"};

// you can get the number of elements in array by dividing its sizeof size (bytes)
// with the size of it's elements in bytes. Just make sure cfgred here is array...
// in the function it is pointer already (arrays get converted to pointers, so
// you can't do this inside the function, you have to do it where you still have
// the original array
int cfgred_len = sizeof cfgred / sizeof(cfgred[0]);

// when you pass array to function, it is automatically converted to pointer, 
// so you must not use & when passing an array like this, otherwise types don't
// match
lora_rf_config(cfgred_len, cfgred);

---

As a side note, always turn on compiler warnings... They help you a lot, fix them. For gcc and clagn, use -Wall -Wextra, for Visual Studio use /W3 or prefereably /W4. And then fix any warnings you get, because they are probably something that doesn't do what you expect.