Thread 1: EXC_BAD_ACCESS (code=1, address=0x0) xCode C++

Question

So I am trying to open a file and parse a file in C++ (using initializeSimulation(). I can open the file successfully, but when I try to parse the file and store specific values from the file into my variables, I get the THREAD 1 error. The DataParser.cpp file is one I am required to use and cannot modify, I am to simply call it. I think the issue is with my function call to getData() (using pointers) but I cannot seem to figure out why. The way my variables are set up now is working weirdly for some reason, until i try to store m_sMaxVal. When I set them all up as pointers, I was getting a different error. I'm new to C++ but please let me know if you need any more information, and thanks in advance.

Simulation.cpp

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include "Simulation.hpp"
#include "dDataParser.h"

Simulation::Simulation() {}
Simulation::~Simulation(){}

void Simulation::initializeSimulation() {

    char *fileName;
    char *m_sType;
    char m_sMaterial;
    int m_iID;
    char m_sUnits;
    double m_sMinVal;
    double *m_sMaxVal;


    cout << "Enter the name of the data file:" << endl;
    cin >> fileName ;
    //cout << fileName << "\n" ;

    parser = new EnviroSimDataParser(fileName);
    parser ->getSensorData(m_sType, &m_sMaterial, &m_iID, &m_sUnits, &m_sMinVal, m_sMaxVal);
}

DataParser.cpp

EnviroSimDataParser::EnviroSimDataParser(char *fileName)
{
char line[128];
strcpy(m_sFileName, fileName); 
inFile = new ifstream();
inFile->open(m_sFileName, fstream::in); // Open the data file
m_iNumSensors = 0;  // Number of sensors in the file
m_iNumDisplays = 0; // Number of display devices in the file
m_iNextSensor = 0;  // Next sensor number to read
m_iNextDisplay = 0; // Next display number to read

if(inFile->is_open())
{
    cout << "file opened successfully1 \n";
    // Count the number of sensors
    while(getNextLine(line, 127))
    {
        if(strcmp(line, "<SENSOR>") == 0)
            m_iNumSensors++;
        if(strcmp(line, "<DISPLAY_DEVICE>") == 0)
            m_iNumDisplays++;
    }

    inFile->close();
    cout << "file closed successfully1 \n";
}
else
{
    cout << "Failed to open file. Application terminated...\n";
    exit(0);
}
}
//-----

bool DataParser::getData(char *type, char *material, int *ID,
        char *units, double *minVal, double *maxVal)
{
    int sNum = 0;
    char line[128];

    // See if we have read all sensors
    if(m_iNextSensor >= m_iNumSensors) return false;

    // Reopen the file
    inFile = new ifstream();
    inFile->open(m_sFileName, fstream::in);
    if(inFile->is_open())
    {
        // Read to the the current sensor count
        while(getNextLine(line, 127))
        {
            if(strcmp(line, "<SENSOR>") == 0) // Got one
            {
                if(sNum == m_iNextSensor)
                {
                    // Get data on this one
                    while(getNextLine(line, 127))
                    {
                        // Get the type
                        if(strcmp(line, "<TYPE>") == 0)
                        {
                            if(getNextLine(line, 127))
                            {
                                strcpy(type, line); // Set the type
                            }
                            else
                                return false; // Oops!
                        }
                        else if(strcmp(line, "<MATERIAL>") == 0)
                        {
                            if(getNextLine(line, 127))
                            {
                                strcpy(material, line); // Set the material
                            }
                            else
                                return false; // Oops!
                        }
                        else if(strcmp(line, "<ID>") == 0)
                        {
                            if(getNextLine(line, 127))
                            {
                                *ID = atoi(line); // Set the ID
                            }
                            else
                                return false; // Oops!
                        }
                        else if(strcmp(line, "<UNITS>") == 0)
                        {
                            if(getNextLine(line, 127))
                            {
                                strcpy(units, line); // Set the units
                            }
                            else
                                return false; // Oops!
                        }
                        else if(strcmp(line, "<MINIMUM_VALUE>") == 0)
                        {
                            if(getNextLine(line, 127))
                            {
                                *minVal = atof(line); // Set the minimum value
                            }
                            else
                                return false; // Oops!
                        }
                        else if(strcmp(line, "<MAXIMUM_VALUE>") == 0)
                        {
                            if(getNextLine(line, 127))
                            {
                                *maxVal = atof(line); // Set the minimum value
                            }
                            else
                                return false; // Oops!
                        }
                        else if(strcmp(line, "</SENSOR>") == 0)
                        {
                            m_iNextSensor++; // Increment for next sensor
                            return true; // Got it
                        }
                    } // end while
                } // end if(sNum == m_iNextSensor)
                else
                {
                    sNum++; // Check the next one
                }
            }
        }
        inFile->close();
    } // end if file open
    return false; // If we get here we have got all the sensors
}

edit: the debugger stops at the line of

*maxVal = atof(line); //Set the minimum value

Answer 1

When a function or method has a parameter that is a pointer to a variable, you need to allocate memory for that variable. There are a few ways to do that, but the easiest one is to declare an automatic variable like this:

double someVar = 0.0;

and call the function that requires a pointer like this:

SomeFunctionThatTakesADoublePointer(&someVar);

You could allocate the memory on the heap by doing:

double* someVar = new double;

and call the function like this:

SomeFunctionThatTakesADoublePointer(someVar);

This comes with a couple of requirements, though. First, you need to check that the allocation succeeded by wrapping the function call in a conditional, like this:

if (someVar != nullptr)
{
    SomeFunctionThatTakesADoublePointer(someVar);
}

And you have to free the memory when you're done using it, or it will leak:

if (someVar != nullptr)
{
    SomeFunctionThatTakesADoublePointer(someVar);
    // ... do some calculating with *someVar
    delete someVar;
}

Things get trickier with character strings. In C++ you should avoid character strings and use std::string from the standard library. (You'll need to #include <string> to use it.) If you must work with character strings because you're calling a function which you don't control and it requires a string, you need to allocate a string that has enough memory for all the characters and the terminating nul character. You can do that on the stack if you know the length of the string is limited by doing something like:

char someString [ MAX_ALLOWED_STRING_LENGTH + 1 ];

where MAX_ALLOWED_STRING_LENGTH is a constant defined somewhere in your program. Then you can call a function or method which takes a character string like this:

SomeFunctionThatTakeACharacterString(someString);

Again, you could allocate the memory using new [], but you have to ensure it's not nullptr before using it and delete [] it when you're done.