passing dynamic 2-dimensional array to function

[bushnellweb]

All I want to do is pass my array "p" which is a 2-dimensional string array to the function changeData().... Can't remember how to pass that. Any ideas?

#include <iostream>
#include <string>
#include <fstream>
#include <new>
#include <iomanip>
 
using namespace std;
 
 
/*
    function: countRecords
    params: string fileName, bool outputTF
    purpose: counts records from passed file name and outputs data if bool is true
*/
int countRecords(string fileName, bool outputTF)
{
    ifstream inFile;
    int recordCount = 0;
 
    inFile.open(fileName.c_str(),ios::in);
    if(inFile.is_open())
    {
        //priming read
        inFile.ignore(1000,'\n');
        recordCount = 1;
 
        //loop
        while(!inFile.eof())
        {
            inFile.ignore(1000,'\n');
            recordCount++;
        }
 
        if(outputTF == true)
        {
            cout << "recordCount= " << recordCount << endl;
        }
 
    }else{ cout << "File would not open!" << endl; }
    inFile.close();
 
    return recordCount;
}
 
void listData(string arr)
{
    cout.setf(ios::left);
    cout << setw(5) << "#" << setw(5) << "ID" << setw(50) << "DESC" << setw(8) << "COST" << setw(6) << "SUPPLY" << endl;
    cout << endl;
 
}
 
void changeData(string arr)
{
    listData(arr);
    system("pause");
}
 
int printMenu()
{
 
    int option = 0;
    cout << endl;
    cout << " 1  Change Data" << endl;
    cout << " 0  Exit" << endl;
 
    cout << "Type number from left to choose operation: ";
    cin >> option;
 
    return option;
}
 
// ***************** MAIN PROCEDURE ***********************
int main()
{
 
    string fileName = "data1.dat";
    int c = countRecords(fileName,false);//one hundred million records MAX
 
    string **p = new string * [c];
    for(int i=0; i<c; i++)
    {
        p[i] = new string [4];
    }
 
    ifstream inFile;
    inFile.open("data1.dat",ios::in);
    if(inFile.is_open())
    {
        while(!inFile.eof())
        {
            for(int i=0; i<c; i++)
            {
                for(int t=0; t<4; t++)
                {
                    if(t==3)
                    {
                        getline(inFile,p[i][t],'\n');
                        //cout << t << ": " << p[i][t] << endl;
                        //system("pause");
                    }else{
                        getline(inFile,p[i][t],'_');
                        //cout << t << ": " << p[i][t] << endl;
                        //system("pause");
                    }
                }//end for t
            }//end for i
        }//end while !eof
 
        int option = printMenu();
        while(option != 0)
        {
            system("cls");
 
            if(option == 1){ changeData(p); } 
            else if(option == 2){ /*function here*/ }
 
            option = printMenu();
        }
    }else{
        cout << "File '" << fileName << "' did not open!" << endl;
        system("pause");
        system("exit");
    }//end if is_open
 
// Memory Cleanup - p
for (int i = 0; i < c; i++)
{
    delete[] p[i];
}
delete[] p;
p = 0;
 
 
 
 
 
 
//return 0
return 0;
}
 

[RedSon]

Are you going to need to pass that by value or by reference?

[Banfa]

Read This

[RedSon]

suryakantb,

Your response was totally off topic and has been deleted.

[bushnellweb]

I WILL need to change the data

[bushnellweb]

changeData(&p);
if that is how i pass it then what do i write in the function args

void changeData(WTF do i write here to accept the array?);

[RedSon]

Did you read the article Banfa posted. Especially the section about "Passing Multi-dimensional Arrays to Functions"

[bushnellweb]

yeah and I've tried passing different ways and the problem is that I don't understand WHY to do those things so it doesn't process in my brain HOW to do what I am doing. I have experimented and failed thats why I am asking for help.

[Banfa]

You appear to be using a variable sized array of array size 4 of strings.

std:string array[N][4];

To pass that to a function you have a number of options, these are limited by the fact tat N is variable but the fact that 4 is not simplifies things a bit. To start with since we will be using 4 a lot we should define a constant with its semantic meaning, that way we can use the constant in our code and should it need to change we only have to change 1 place. I believe the type of array indexes is int so declare

const int SOME_MEANINGFUL_NAME = 4;

Since this is constant we can included it has part of the type passed to the function rather than pass the size of the second dimension as a parameter so for the first parameter of our function what we will do is write our array type leaving out the dimensions we don't know and passing a size parameter for each of the unknown dimensions

void function(std:string pointer[][SOME_MEANINGFUL_NAME], int size);

And actually that is it because in a function parameter list the left most set of [] is allowed to be empty. it declares a pointer to type, this is its equivalent to

void function(std:string (*pointer)[SOME_MEANINGFUL_NAME], int size);

Note the parenthesis are required in this syntax otherwise you declare an array of pointers rather than a pointer to an array.

It gets a little more complex if you have 2 or more unknown array dimensions.


However since you are using string you must be using C++ and if you are using C++ you should be using vectors not arrays. They handle all the memory management for you and generally make things easier.

#include <iostream>
#include <string>
#include <vector>
 
using namespace std;
 
const int SOME_MEANINGFUL_NAME = 4;
 
// The C++ Way
void func1(vector<vector<string> >& vec)
{
    vector<vector<string> >::iterator outer;
 
    for(outer = vec.begin(); outer != vec.end(); outer++)
    {
        vector<string>::iterator inter;
 
        for(inter = outer->begin(); inter != outer->end(); inter++)
        {
            cout << *inter << endl;
        }
    }
}
 
// The C Way
void func2(vector<vector<string> >& vec)
{
    vector<vector<string> >::size_type outer;
 
    for(outer = 0; outer < vec.size(); outer++)
    {
        vector<string>::size_type inter;
 
        for(inter = 0; inter < vec[outer].size(); inter++)
        {
            cout << vec[outer][inter] << endl;
        }
    }
}
 
int main()
{
    string fileName = "data1.dat";
    int c = 20; //countRecords(fileName,false);//one hundred million records MAX
 
    vector<vector<string> > vec;
 
    vector<string> initialiser; // Something we can use to initialise our main vector
 
    initialiser.resize(SOME_MEANINGFUL_NAME);
 
    vec.resize(c, initialiser);
 
    func1(vec);
    func2(vec);
}
 

[bushnellweb]

Error 1 error C2664: 'changeData' : cannot convert parameter 1 from 'std::string **' to 'std::string (*)[4]' c:\users\nick\documents\visual studio 2005\projects\nrsproject_001\nrsproject_001\main.c pp 117

Thats the error I get when doing this:

 
void changeData(string (*arr)[4])
{
     // why even bother getting a c++ job
     system("pause");
}
 
int main()
{
 
     int c = countRecords(fileName,false);//one hundred million records MAX
 
     string **p = new string * [c];
     for(int i=0; i<c; i++)
     {
          p[i] = new string [4];
     }
 
     changeData(p);
 
 
 

[Banfa]

That is because p is not a pointer to an array of 4 string, string(*)[4], it is a pointer to a pointer to a string. Neither is *p. You need to change your declaration of p to a more specific type, to wit a pointer to string[4] like so

string (*p)[SOME_MEANINGFUL_NAME];

You can allocate the entire array with

p = new string [10][SOME_MEANINGFUL_NAME];

You no longer need a loop to allocate all the little sub arrays.

[bushnellweb]

thanks for the help I got it working..just had to read it a few times. How come c++ is so complicated? In any other language a multi-dim array takes 3 minutes to figure out