GSM incoming bytes from UART not complete

Question

I have used AT commands to read incoming bytes from serial buffer from SIM900A but I cannot get the complete message using the code below:

while(ss.available()>0)
{
 inChar=ss.read();
 inString+=inChar;
}

Serial.println("Received messaged: ");
Serial.println(inString);

inString="";

However this one below works:

if(ss.available()>0)
{
  inString=ss.readString();
}

Serial.println("Received messaged: ");
Serial.println(inString);

inString="";

I wonder what is the difference?

Answer 1

The data arrive over serial very slow compared to MCU speed. In the first snippet you stop reading at first gap between bytes (available is 0). In the second snippet the function readString will wait for the next byte until a second (at default).