serialPutchar with char* variable

I need to send char* (command) with serial WiringPi. How do I do it if serialPutchar (int fd, unsigned char c) needs an unsigned char?

int SendCommand(int serial, char *command, char *expectedResponse, char response []) {
   serialFlush(serial);
   serialPutchar(serial, command);
   return 1;
}

I still have something wrong with my code that I don't know what it is.

I use SendCommand function to send data to a server. However, I send an empty NULL packet when I try to send 'a'.

I don't understand :(

int SendCommand(int serial, char *command,  char *expectedResponse, char response []) {
   int max_Retries = 0;
   int i;
   char data[256], *pData = data;

   serialFlush(serial);

   for(i = 0; i <= strlen(command); i++) {
       serialPutchar(serial, command[i]);
   }
   delay(100);

   while(serialDataAvail(serial)){ 
      *pData++ = serialGetchar(serial);
   }        

      while(strstr(data, expectedResponse) == (const char*) NULL){ 
         if(max_Retries >= 150) {          
            printf("\nSIM7070_SendCommand - The expected response hasn't been found\n");
            return 0;
         }
                 
        else{
           *pData++ = serialGetchar(serial);
            max_Retries++;
            delay(100);
        }

      }            
      if(strstr(data, expectedResponse) != (const char*) NULL){  
         *pData= '\0';
         printf ("%s", data);                  
         printf("\nSIM7070_SendCommand - The expected response has been found\n");
         
         if(response != NULL){
            strcpy(response, data);
         }   
         return 1;                   
               
      }
      return 0; 
}

   SendCommand(serial, "AT+CASEND=1,1\r\n", ">", NULL);
   serialFlush(serial);
   serialPutchar(serial,'a');
   serialFlush(serial);

Solution

A char* is a pointer to a char type. It might be both an array of char or a single char. Your command is probably a ponter to an array, so you will need to loop over it or use a better serial sender which accepts strings and not single chars.

Loop over string

There are several ways to loop a C string. This one uses a i variable which increases from 0 until the string length (got using strlen(command)):

int SendCommand(int serial, char *command, char *expectedResponse, char response []) {
   int i;
   serialFlush(serial);
   // Use <= to send also the `0` string terminating char
   for(i = 0; i <= strlen(command); i++) {
       serialPutchar(serial, command[i]);
   }
   return 1;
}

You could also:

Use a pointer initially pointing to command and increment it until finding a 0 character (end of line).
Use a decrementing variable (counting from command's length until 0), so you only get the length once (optimized).

Use a better serial sender

Here, I use serialPuts to send the full string at once:

int SendCommand(int serial, char *command, char *expectedResponse, char response []) {
   serialFlush(serial);
   serialPuts(serial, command);
   return 1;
}