程序停止工作，我确定指针错误

Question

I have this program, and I'm still getting used to C++ pointers, so It's probably an issue with that. But I am having the program crash when the getStructData() function is called. I've probably messed up something to do with the pointer to the struct that i've used, but I'm really not sure at this point. Any tips or help are appreciated. Thanks, and before people start the mad downvoting, this isn't a homework assignment from my school, I'm just going over other schools homework to practice during the christmas break.

Prog1Struct.h

#ifndef INCLUDED_PROG1STRUCT
#define INCLUDED_PROG1STRUCT

struct Prog1Struct
{

int m_iVal;
double m_dArray[5];
char m_sLine[80];

};

#endif

Prog1Class.h

#ifndef PROG1CLASS
#define PROG1CLASS
#include "Prog1Struct.h"



class Prog1Class
{

private:
Prog1Struct myStruct[5];



public:

/*Prog1Class();
~Prog1Class();*/
void setStructData();
void getStructData(int structureArrayIndex, struct Prog1Struct *info);
void printStruct(int indexPriv);
void printData(); 

};

#endif

Prog1Class.cpp

#ifndef INCLUDED_PROG1CLASS
#define INCLUDED_PROG1CLASS

#include <iostream>
#include <string>
#include "Prog1Class.h"
#include "Prog1Struct.h"
#include <time.h>

using namespace std;




void Prog1Class::setStructData()
{
for (int i = 0; i<5; i++)
{
cout << "Enter an integer: ";
cin >> myStruct[i].m_iVal;
for (int j = 0; j < 5; j++)
{
    cout << endl << "Enter a double: ";
    cin >> myStruct[i].m_dArray[j];
}
cout << endl << "Enter a string: ";
cin.ignore(256, '\n');
cin.getline(myStruct[i].m_sLine, 80, '\n');
cout << endl;
}
}

//takes in index for array, and pointer to a struct of the type in Prog1Struct.h.  Copies     all data from the private struct at the given index into the struct of the pointer     argument.
void Prog1Class::getStructData(int structureArrayIndex, struct Prog1Struct *info)
{

*info = myStruct[structureArrayIndex];
cout << "Printing *info from getStructData function" << endl;
cout << info;
}


void Prog1Class::printStruct(int indexPriv)
{
cout << myStruct[indexPriv].m_iVal << " ";
for (int k = 0; k < 5; k++)
{
cout << myStruct[indexPriv].m_dArray[k] << " ";
}
cout << myStruct[indexPriv].m_sLine << " ";
}


int main(void)
{
Prog1Class c;
Prog1Struct *emptyStruct = '\0';
cout << "setStructData called:" << endl;
c.setStructData();
cout << "getStructData called:" << endl;
//error comes here, at getStructData.  
c.getStructData(2, emptyStruct);
cout << "printStruct called:" << endl;
c.printStruct(2);


cin.get();
}



#endif

Answer 1

You are trying to assign a value to a null pointer.

Prog1Struct *emptyStruct = '\0';//set emptyStruct to 0 (This means it points at address 0, not holding a 0 value)
cout << "setStructData called:" << endl;
c.setStructData();
cout << "getStructData called:" << endl;
//error comes here, at getStructData.  
c.getStructData(2, emptyStruct);//emptyStruct is still = 0

So in the function, info = 0.

void Prog1Class::getStructData(int structureArrayIndex, struct Prog1Struct *info)
{

*info = myStruct[structureArrayIndex];//This line is trying to write to a section of memory you don't have access to (address 0)

I think you want this instead. (untested) This will make info point to myStruct[structureArrayIndex] (Not copy the contents of myStruct[structureArrayIndex] to info). Pointers only point to things (like structs or some other type), they cannot contain a struct.

info = &myStruct[structureArrayIndex];