Dynamic Memory Allocation: Array Initialization

[alexyoung1992]

Hi guys,

So I'm trying to learn how to use dynamic memory allocation with arrays.
In this project, I am trying to read a list of numbers from a file into a dynamically allocated array, and then print out the numbers, sorted in ascending order.

I'm having a problem reading into the array.

This is my code:

#include<iostream>
#include<iomanip>
#include<fstream>
#include<string>
#include<new>

using namespace std ;

bool OpenFile(ifstream &) ;
void ReadFile(ifstream &, float [], int) ;
void Print(float [], int) ;
int CalcSize(ifstream &) ;
void BubbleSort(float [], int) ;

int main()
{
    ifstream    fin ;
    float *     dArray = NULL;
    int         size ;
    size = CalcSize(fin) ;
    dArray = new (nothrow) float[size] () ;
    if(dArray == 0)
        cout << "Error: memory could not be allocated." ;
    else
    {
        ReadFile(fin, dArray, size) ;
        Print(dArray, size) ;
        
        delete [] dArray ;
        dArray = NULL ;
    }
} // end Function main

bool OpenFile(ifstream &fin)
{
	string inputFile ;
	int opentrys = 3 ;
	
	cout << endl << "Please enter the name of the input file: " ;
	getline(cin, inputFile) ;
	fin.open(inputFile.c_str()) ;
	
	if (fin.fail())
	{
		while (fin.fail())
		{
			if (opentrys == 0)
			{
				cout << endl << "0 attempts remaining. Please try again later." << endl << endl ;
				return false ;
                exit(1) ;
			}
			cout << endl << "You inputted a bad file name. (" << opentrys << " attempts remaining)" << endl ;
			cout << "Please enter the name of the input file: " ;
			cin >> inputFile ;
			fin.open(inputFile.c_str()) ;
			opentrys-- ;
		} // While loop
		return true ;
	} // If statement
	else 
		return true ;
} // end Function OpenFile

int CalcSize(ifstream & fin)
{
    int x ;
    int counter = 1 ;
    if(OpenFile(fin))
    {
        fin >> x ;
        if(fin.eof())
        {
            cout << endl << "The file was empty." ;
            exit(1) ;
        }
        while(!fin.eof())
        {
            counter++ ;
            fin >> x ;
        }
    }
    return counter ;
} // end Function CalcSize

void ReadFile(ifstream & fin, float data[], int size)
{
    int i = 0 ;
    fin >> data[i] ;
    while(!fin.eof())
    {
        fin.ignore(10, '\n') ;
        fin >> data[++i] ;
    } // While Loop
} // end Function ReadFile

void Print(float data[], int size)
{
    BubbleSort(data, size) ;
    cout << endl << "The file contains the following numbers: " ;
    for(int i = 0; i < size-1; i++)
        cout << data[i] << ", " ;
    cout << data[size-1] << "." << endl << endl ;
}

void BubbleSort(float list[], int size)
{
	int temp ;
	bool flag ;
	do
	{
		flag = false ;
		size-- ;
		for (int i=0; i<size; i++)
			if (list[i] > list[i+1])
			{
				temp = list[i] ;
				list[i] = list[i+1];
				list[i+1] = temp ;
				flag = true ;
			}
	} while (flag) ;
} // end Function BubbleSort 

and here's what it outputs:

The file contains the following numbers: 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.

Before I added "()" to the end of this line: dArray = new (nothrow) float[size] () ;, it just printed out garbage, but now it prints out zeros instead. I feel like the problem is with reading into the array from the file, but I can't seem to fix it.

Thanks for your help guys.

[flclempire]

What exactly does is this for in the Read function? I know what the function does, I'm just not sure why you're using it here.

fin.ignore(10, '\n') ;

Also, you should post an example of your files format.

[alexyoung1992]

My input file is formatted like so:

2
72
51
45
9
12
34
4
4536

so the fin.ignore(10, '\n') ; ignores all the excess garbage get lines and cin's, etc can pick up until the next line. By the way, I tried taking the fin.ignore out and it's still printing out zeros.

Oh, and what do you mean by files format, I'm not using any header files or anything, just compiling one .cpp file if that's what you mean?

Also, I tried changing my entire read function to this, still to no avail:

void ReadFile(ifstream & fin, float data[], int size)
{
    for(int i = 0; i < size; i++)
    {
        fin >> data[i] ;
        fin.ignore(10, '\n') ;
    }
} // end Function ReadFile 

[sasanet]

dArray = new (nothrow) float[size] () ;
how did u do this if "size" is undefined??
ok here what fin >> x; means ??

int CalcSize(ifstream & fin)
{
    int x ;
    int counter = 1 ;
    if(OpenFile(fin))
    {
        fin >> x ;
        if(fin.eof())
        {
            cout << endl << "The file was empty." ;
            exit(1) ;
        }
        while(!fin.eof())
        {
            counter++ ;
            fin >> x ;
        }
    }
    return counter ;
} // end Function CalcSize 

put this code between line 21 and 22
it will "clean" up new array (to 0)

void clean (float arr []) {
           for (short i = 0; i < size; i++)
                  arr [i] = 0;
}

now change read file function:

void ReadFile(ifstream & fin, float data[], int size)
{
    int i = 0 ;
    while(!fin.eof())
    {
        fin >> data[i++] ;
    }
}

here for (...) will stop when get to 0 (from clean function)

void Print(float data[], int size)
{
    BubbleSort(data, size) ;
    cout << endl << "The file contains the following numbers: " ;
     short i = 0;
   while (data [i] != 0 || i < size - 1)  //0 = no more inputs
        cout << data[i++] << ", " ;

    cout << data[size-1] << "." << endl << endl ;
}

change:
dArray = new (nothrow) float[size] () ;
with
dArray = new float[size];
not shure if this help but try it out.