Store SMS message in variable

I’m having trouble saving an SMS message to a variable. The idea is to send an SMS with a command and later use a conditional operator to activate or deactivate a relay.

But I can not save the SMS message. Whenever I try to save it, it assumes the value of:

" ÿ " .

I’m using a sim900 GSM module with Arduino.

Here is the code I’m trying to use:

#include <SoftwareSerial.h>
SoftwareSerial cell(2,3); 
void setup()
{
    cell.begin(19200);
    cell.println("AT+CMGF=1"); 
    delay(200);
    cell.println("AT+CNMI=3,2,0,0");
    delay(200);
}
void loop() 
{
    if(cell.available() >0)    // se o shild resceber uma msg
    {          
        delay(10);
        msg=cell.read();     // salve ela na variavel  msg
        Serial.println(msg);// mostra o valor do "msg" NESSE ponto ela esta valendo ÿ 
        if (msg=='a')     // se o primeiro caracter for "a"
        {
            delay(10);
            msg=cell.read();
            if (msg=='0')   // se o segundo caracter for "0"
            {
                delay(10);
                msg=cell.read();
                if (msg=='e')   // se o terceiro caracter for "e"
                {
                }
            }
        }
    }
}

When I print the message on the serial, its value is ÿ , why this?

I researched and found that before telling Arduino to store the SMS, we have to tell him to “listen” to the serial that receives the message and this is related to:

gsm.listen(); 

But I did not understand the relationship very well.

This code solves my problem, I can edit the sms. using vectors:)

#include <SoftwareSerial.h>
SoftwareSerial SIM(2, 3);
int x =0;
float temp=0;
char data [256];

void loop()
{
  Serial.println("ler mensagem");
  delay(1000); 
  //mySerial.flush();
  for (x=0;x < 255;x++)
  {
    data[x]='
#include <SoftwareSerial.h>
SoftwareSerial SIM(2, 3);
int x =0;
float temp=0;
char data [256];

void loop()
{
  Serial.println("ler mensagem");
  delay(1000); 
  //mySerial.flush();
  for (x=0;x < 255;x++)
  {
    data[x]='%pre%';
  }
  x=0;
  do{
while(SIM.available()==0);
data[x]=SIM.read();
x++;
if(data[x-1]==0x0D&&data[x-2]=='"') 
{ 
 x=0;
}
}
while(!(data[x-1]=='K'&&data[x-2]=='O')); 
  data[x-3]='%pre%'; 
  Serial.println(data[1]);
 temp=0;
 temp=data[7];
Serial.println(temp); 

';

  }

  x=0;

  do{

while(SIM.available()==0);

data[x]=SIM.read();

x++;

if(data[x-1]==0x0D&&data[x-2]=='"')

{

 x=0;

}

}

while(!(data[x-1]=='K'&&data[x-2]=='O'));

  data[x-3]='%pre%';

  Serial.println(data[1]);

 temp=0;

 temp=data[7];

Serial.println(temp);



    

I think 'ÿ' has the value -1 .

According to the documentation for SoftwareSerial: read

  

Returns
  the character read, or -1 if none is available

If the function returns -1 it means that there are no characters available.

    msg = cell.read();
    if (msg == -1) /* nao ha caracteres disponiveis */;