void function that read a file into a 2-dimensinal array

[mathanne]

hi, I need help in creating a void function that read from a file into a two dimensional array. I'm ok when I create the function declaration but it gets confusing when I need to put the actual read statement. I don't know if I have to declare a variable for each column or if by setting the array it does it automatically.

PLEASE HELP!!!

[gpraghuram]

hi, I need help in creating a void function that read from a file into a two dimensional array. I'm ok when I create the function declaration but it gets confusing when I need to put the actual read statement. I don't know if I have to declare a variable for each column or if by setting the array it does it automatically.

PLEASE HELP!!!

If u are using an arry then u need not declare a variable for every element.
Use a common elemnt to read values from the file and store the value to the array by incrementing the index for every read.

Raghuram

[mathanne]

thanks for helping Raghuram, I initialized the array with for loop that incremented the index but I don't know what should I put in the actual input statement here is the incomplete void function because I stuck :( !!!

void getData (ifstream& inData, int temp[nOfRows][nOfColumns], const int nOfRows)
{
     int r, c;
     int high, low;
 
 
     for (r = 0; r < nOfRows; r++)
         for (c = 0; c < nOfColumns; c++)
 
 
}

any ideas???

[gpraghuram]

thanks for helping Raghuram, I initialized the array with for loop that incremented the index but I don't know what should I put in the actual input statement here is the incomplete void function because I stuck :( !!!

void getData (ifstream& inData, int temp[nOfRows][nOfColumns], const int nOfRows)
{
int r, c;
int high, low;


for (r = 0; r < nOfRows; r++)
for (c = 0; c < nOfColumns; c++)


}

any ideas???

I was not suggesting the way you have replied.
First you shuld get a fair idea about how to read from a file using the stdio file operations.
Then you can get an idea about how to go about this an u can understand the idea explained by me or you can get a better idea


Raghuram

[mkborregaard]

hi, I need help in creating a void function that read from a file into a two dimensional array. I'm ok when I create the function declaration but it gets confusing when I need to put the actual read statement. I don't know if I have to declare a variable for each column or if by setting the array it does it automatically.

PLEASE HELP!!!

Hi Mathanne,
It is not clear for me what you want to acheive exactly, but let me try to give you a few points:
If programming in c++, you should use a <vector> instead of an array, it is a much more easy-to-use and powerful container. You could define it as:

#include <vector>
typedef std:vector<std.vector<int> > 2Dvector;
2Dvector myArray;

provided that it is int you want to store in your vector.

<The rest of this post was providing 'spoonfed code', which violates our Posting Guidelines, and has been removed. MODERATOR>

I am assuming that your file looks something like this:
1 5 21 23 17
4 5 6 12 12
4 95 23 23 43
87 1 2 3 51

/m

[mkborregaard]

Cool enough,
I will abstain from spoonfed code.
Mathanna,
you open the file as a std:ifstream ; then you can read the file using the >> operator, and fill the 2Dvector using

myArray.push_back();

alternatively, you can construct the vector as:

std:vector<std:vector<int> > myArray(cols,std:vector<int>(rows));

and just fill it in your for loops using the index [][] operator.

[mathanne]

Thanks for the ideas, but I can't use them since we haven't started to use vectors in programs. The exercise just says to write a function that reads and stores data in a 2-dimensional array.

Mathanne.

[weaknessforcats]

The exercise just says to write a function that reads and stores data in a 2-dimensional array.

Read this:

First, there are only one-dimensional arrays in C or C++. The number of elements in put between brackets:

int array[5];
 

That is an array of 5 elements each of which is an int.

int array[];
 

won't compile. You need to declare the number of elements.

Second, this array:

int array[5][10];
 

is still an array of 5 elements. Each element is an array of 10 int.

int array[5][10][15];
 

is still an array of 5 elements. Each element is an array of 10 elements where each element is an array of 15 int.

int array[][10];
 

won't compile. You need to declare the number of elements.

Third, the name of an array is the address of element 0

int array[5];
 

Here array is the address of array[0]. Since array[0] is an int, array is the address of an int. You can assign the name array to an int*.

int array[5][10];
 

Here array is the address of array[0]. Since array[0] is an array of 10 int, array is the address of an array of 10 int. You can assign the name array to a pointer to an array of 10 int:

int array[5][10];
 
int (*ptr)[10] = array;
 

Fourth, when the number of elements is not known at compile time, you create the array dynamically:

int* array = new int[value];
int (*ptr)[10] = new int[value][10];
int (*ptr)[10][15] = new int[value][10][15];
 

In each case value is the number of elements. Any other brackets only describe the elements.

Using an int** for an array of arrays is incorrect and produces wrong answers using pointer arithmetic. The compiler knows this so it won't compile this code:

int** ptr = new int[value][10];    //ERROR
 

new returns the address of an array of 10 int and that isn't the same as an int**.

Likewise:

int*** ptr = new int[value][10][15];    //ERROR
 

new returns the address of an array of 10 elements where each element is an array of 15 int and that isn't the same as an int***.

With the above in mind this array:

int array[10] = {0,1,2,3,4,5,6,7,8,9};
 

has a memory layout of

0 1 2 3 4 5 6 7 8 9

Wheras this array:

int array[5][2] = {0,1,2,3,4,5,6,7,8,9};
 

has a memory layout of

0 1 2 3 4 5 6 7 8 9

Kinda the same, right?

So if your disc file contains

0 1 2 3 4 5 6 7 8 9

Does it make a difference wheher you read into a one-dimensional array or a two-dimensional array? No.

Therefore, when you do your read use the address of array[0][0] and read as though you have a one-dimensional array and the values will be in the correct locations.