String extraction issue in Arduino - c++

Question

I have the following Arduino code
#include "SIM900.h"
#include <SoftwareSerial.h>
#include "inetGSM.h"
#include<String.h>
InetGSM inet;
char msg[165];
char store[2];
char a;
char b;
char* disp;
boolean started=false;
void setup()
{
//Serial connection.
Serial.begin(9600);
Serial.println("GSM Shield testing.");
//Start configuration of shield with baudrate.
//For http uses is raccomanded to use 4800 or slower.
if (gsm.begin(2400)) {
Serial.println("\nstatus=READY");
started=true;
} else Serial.println("\nstatus=IDLE");
if(started)
{
//GPRS attach, put in order APN, username and password.
//If no needed auth let them blank.
if (inet.attachGPRS("TATA.DOCOMO.INTERNET", "", ""))
Serial.println("status=ATTACHED");
else Serial.println("status=ERROR");
delay(1000);
//TCP Client GET, send a GET request to the server and
//save the reply.
inet.httpGET("www.boat.esy.es", 80, "/retrieve.php", msg, 165);
//Print the results.
Serial.println("\nData received:");
disp = strstr(msg,"\r\n\r\n");
disp = disp+4;
a = disp[1];
b = disp[2];
}
}
void loop()
{
Serial.println("Begin");
Serial.println(a);
Serial.println("+");
Serial.println(b);
Serial.println("End");
delay(500);
}
The disp variable in my program accepts the value 1 & 1 as string. I want this 1 & 1 to be stored in two separate variables. SO I tried the way mentioned above and this is what I got
Output
Begin
1
+
End
Begin
1
+
End
Begin
1
+
End
If I understand array correctly, char arr[100] is same as char* arr, just that the former one reserves 100 character locations on the memory, then b = disp[2] should give the latter 1 of 11 right?
I am not trying to use the String library because that will occupy a lot of memory. So if there's any way that I'm not aware of that extract both the 1s & store them separately, please let me know.
Thank you for your time!

Answer 1

Your code is almost correct.
The problem is here:
disp = strstr(msg,"\r\n\r\n");
disp = disp+4; // now disp points to the string "11" (correct)
// what follows is wrong
a = disp[1]; // this is the second char element if the disp string
b = disp[2]; // this is the zero terminator of the disp string
You need this because in C arrays indexes start with 0:
a = disp[0];
b = disp[1];
Small test program:
#include <stdio.h>
#include <string.h>
int main()
{
char *disp;
char msg[] = "Fake Header\r\n\r\n12";
char a;
char b;
disp = strstr(msg,"\r\n\r\n");
disp = disp+4;
a = disp[0];
b = disp[1];
printf("a = %c\nb = %c\n", a, b);
return 0;
}
Output:
a = 1
b = 2

Answer 2

There are quite a few problems with your code here...
Firstly, all your variables are un-initialised and you're accessing them after their declaration without initially giving them any value in memory. To solve this set each variable to something before you continue on like so:
char a = ''; // & so on...
Next up, char* disp; is a pointer, not a variable. You dont actually know the physical location of disp, it points to somewhere it memory, maybe a bit of populated memory, maybe nothing at all. So the best way to store something in disp is to turn it into an array and they write to it part by part reading when you need and terminating the variable with the correct formatting.
e.g
char disp[2] = {}; // Declare disp...
disp[0] = '1'; // Write to disp...
disp[1] = '1';
disp[2] = '\0';
& finally the webserver you're connecting too has DynDNS attached to the address, and anybody can access it without a password and anybody can start attacking it, so I would hide it.