std::out_of_range error in c++ code using libserial library

Question

I am kind of new at c++. I have been using a library to handle serial communication in UNIX environments called libserial. I made a very simple test to try the library writing something to a peripheral and receiving an answer. The test went pretty well...code is shown below:

#include <SerialStream.h>
#include <iostream>
#include <string>
#include <unistd.h>
#include <cstdlib>

using namespace LibSerial ;


int main(int argc, char** argv)
{
SerialStream serial_port;
/*Open the serial port for communication*/
serial_port.Open( "/dev/ttyTHS2" );

/*Setting the baud rate*/
serial_port.SetBaudRate(SerialStreamBuf::BAUD_9600);

/*Setting the character size*/
serial_port.SetCharSize(SerialStreamBuf::CHAR_SIZE_8);

/*Setting number of stop bits*/
serial_port.SetNumOfStopBits(1);

/*Setting parity type*/
serial_port.SetParity(SerialStreamBuf::PARITY_NONE);

/*Setting Flow Control managment*/
serial_port.SetFlowControl( SerialStreamBuf::FLOW_CONTROL_NONE) ;

/*WRITTING ROUTINE*/

/*Requesting the TID of the current TAG*/
serial_port.write( "\r", 1);
serial_port.write( "021400", 6);
serial_port.write( "\r", 1);

/*READING RESPONSE FROM PERIPHERAL
const int BUFFER_SIZE = 256;
char input_buffer[BUFFER_SIZE];
serial_port.read(input_buffer, BUFFER_SIZE);
std::string input(input_buffer);
std::string TID = input.substr(5,16);
std::cout << "Current TAG identifier: " << TID << "\n";

/*Closing serial port*/
serial_port.Close();
return 0;

}

Since I want to perform more than a write/read operation...I decided to use functions in order to optimize the code and make it easier to change. My new optimized version is shown below:

#include <SerialStream.h>
#include <iostream>
#include <string>
#include <unistd.h>
#include <cstdlib>

using namespace LibSerial ;
using namespace std;

/*Function declaration*/
void serial_setup();
void serial_read();

int main(int argc, char** argv)
{
    SerialStream serial_port;
    /*SETUP BAUD RATE, PARITY BITS, ETC.
    serial_setup();

     /*Requesting the TID of the current TAG*/
    serial_port.write( "\r", 1);
    serial_port.write( "021400", 6);
    serial_port.write( "\r", 1);

    /*Read response from peripheral
    serial_read();

   /*Closing serial port*/
    serial_port.Close();
    return 0;

}

void serial_setup(){
    SerialStream serial_port;

    /*Open the serial port for communication*/
    serial_port.Open( "/dev/ttyTHS2" );

    /*Setting the baud rate*/
    serial_port.SetBaudRate(SerialStreamBuf::BAUD_9600);

    /*Setting the character size*/
    serial_port.SetCharSize(SerialStreamBuf::CHAR_SIZE_8);

    /*Setting number of stop bits*/
    serial_port.SetNumOfStopBits(1);

    /*Setting parity type*/
    serial_port.SetParity(SerialStreamBuf::PARITY_NONE);

    /*Setting Flow Control managment*/
    serial_port.SetFlowControl( SerialStreamBuf::FLOW_CONTROL_NONE) ;
}

void serial_read(){
    SerialStream serial_port;

    const int BUFFER_SIZE = 256;
    char input_buffer[BUFFER_SIZE];
    serial_port.read(input_buffer, BUFFER_SIZE);
    string input(input_buffer);
    string TID = input.substr(5,16);
    cout << "Current TAG identifier: " << TID << "\n";
}

The problem is that somehow, probably there is a condition that is not verified in one of the functions and is throwing the following error when executing:

    terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 5) > this->size() (which is 3)
Aborted (core dumped)

I do not think is something related to a bad usage of the library rather than a bad creation of function from my part. I have been changing several things without any luck and it will really help me if you have any idea of where the out of range condition is happening.

You now have two `SerialStream`s: `serial_setup()` creates a stream object, opens up a port, sets the baud rates, then at the end of the function it goes out of scope and probably closes up the port. Next, `serial_read()` creates a new stream object, never connects it to a physical port, then tries to read from a non-existent port, and fails. (Strictly speaking, the class might not work like that, but the above is the most likely scenario.) — Ken Y-N, Aug 22 '17 at 00:00
Excellent explanation Ken Y-N, it makes total sense analyzing it that way. Solve it using VTT proposal. — Daniel Lara, Aug 22 '17 at 00:26

score 1 · Accepted Answer · answered Aug 21 '17 at 23:58

1

main, serial_setup and serial_read functions work with their own local SerialStream variables so changes are not preserved. You should pass SerialStream instance from main by reference:

void serial_setup(SerialStream & serial_port){

void serial_read(SerialStream & serial_port){

Or actually wrap up SerialStream into object with serial_setup becoming constructor, serial_read becoming method and serial_port.Close(); becoming destructor.

answered Aug 21 '17 at 23:58

user7860670

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Thank you very much for the assistance. I should declare in that way the functions outside the main and then whenever I call the function from the main i should call it as serial_setup(serial_port)? – Daniel Lara Aug 22 '17 at 00:14
Yes. This way all functions will use `serial_port` declared in `main`. – user7860670 Aug 22 '17 at 00:16
Nevermind...I confirm this works. Thank you very much VTT! – Daniel Lara Aug 22 '17 at 00:21

std::out_of_range error in c++ code using libserial library

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