CODEWITHSUNDEEP
c++arrayspointersstructaccess-violation
Roopan
Roopan

Reputation: 13

FIXED: Access Violation Reading Location (pointer to string array)

FIXED: http://pastebin.com/71QxqGk5

first post/question.

So this is C++ and I am trying to print an array of words.

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <string>
#include <cstring>
#include <cctype>
#include <ctime>
using namespace std;

//structs
struct Input
{
    int size;
    string* word;
    bool is_palindrome[];
};

//prototypes
bool openInputFile(ifstream &ifs);
void File_to_Array(string* word, int &size);
void PrintArray(string* word, int size);

//main
int main()
{
    Input myInput = { 0, nullptr, false };
    File_to_Array(myInput.word, myInput.size);//copy arr and get size
    cout << myInput.word; //this outputs 00000000
    cout << *myInput.word; //this breaks and throws exception as commented below

    //Exception thrown at 0x0098BB6B in Project1.exe: 0xC0000005: Access violation reading location 0x00000014.

    PrintArray(myInput.word, myInput.size);//print array of strings

    system("PAUSE");
    return 0;
}

//functions
bool openInputFile(ifstream &ifs)
{
    string filename;

    cout << "Enter the input filename: " << endl;
    getline(cin, filename);
    ifs.open(filename.c_str());
    return ifs.is_open();
}

void File_to_Array(string* word, int &size)//copies file to dyn arr and assigns size from first elem
{
    ifstream myFile;
    while (!openInputFile(myFile))
        cout << "Could not open file" << endl;
    string tempstr = "";
    getline(myFile, tempstr);//first line is size of dyn arr
    size = stoi(tempstr);//now we have max size of dyn arr of strings
    word = new string [size];//now we have the array of strings, *word[index] = string1
    int i;
    for (i = 0; getline(myFile, word[i]) && i < size; ++i);//for each line
    //copy line of string from file to string arr within "bool" test, second param of for loop  //copying done
    size = i;
    myFile.close();//done with file, no need, close it
}

void PrintArray(string* word, int size)
{
    //for (int i = 0; i < size; ++i)
    //cout used to be here, but now its in main, for debugging
}

So I'm wondering if my problem is with passing a member of a struct, and if I should have instead passed the entire struct type "myInput" into the functions and use the -> operator to access the members of myInput.

below is an example of a text file

5
month
Runner
NEON
digit
ferret
nothing

the 5 would be the size of the dynamically allocated array, the rest are strings, as you can see there are 6 strings, so I have in the for loop a test for whether the file is still transferring strings to the array.

Upvotes: 1

Views: 1455

Answers (1)

SingerOfTheFall
SingerOfTheFall

Reputation: 29966

This part of the File_to_Array is causing the problem:

word = new string [size];

You think that you are setting the pointer of myInput object to point to the string array, but you're not. When you pass the pointer to the function here:

File_to_Array(myInput.word, myInput.size)
              ^^^^^^^^^^^^

you are really passing a copy of the pointer. So inside the File_to_Array, this copy is re-pointed to the newly-created string array, but the real pointer inside myInput is not changed. You should pass a reference to the pointer instead:

void File_to_Array(string*& word, int &size)
                   \___________/
                         ^--reference to a pointer

I would also suggest you to use a vector[string] instead. Finally, your bool is_palindrome[]; member and it's initialization look very strange, but it's hard to comment further since they are never used in the code.

Upvotes: 1

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