how can I pass an array pointer to a function

Question

#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>


using namespace std;

typedef vector <double> record_t;
typedef vector <record_t> data_t;


int sorted(int *data,int max_record_size)
{


}




int main()
{
    // Here is the data we want.
    data_t data;

    // Here is the file containing the data. Read it into data.
    ifstream infile( "sort.txt" );
    infile >> data;

    // Complain if something went wrong.
    if (!infile.eof())
    {
        cout << "Fooey!\n";
        return 1;
    }

    infile.close();

    // Otherwise, list some basic information about the file.
    cout << "Your CSV file contains " << data.size() << " records.\n";



    unsigned max_record_size = 0;
    for (unsigned n = 0; n < data.size(); n++)
        if (max_record_size < data[ n ].size())
            max_record_size = data[ n ].size();
    cout << "The largest record has " << max_record_size << " fields.\n";
    int i;
    for (i=0; i <= max_record_size; i++)
    {

        cout << "your data contains " << data[ 0 ][ i ] << ".\n";
        int temp[max_record_size];

        sorted(&data,max_record_size);

        //cout << "Your sorted data contains" << sorted [0] [i] << ".\n";
    }


    cout << "Good bye!\n";
    system("PAUSE");

    return 0;
}

cannot convert data_t*' toint*' for argument 1' toint sorted(int*, int)'

Im trying to pass the pointer of my data which should be an array containing my list of numbers to my sort function what exactly am I doing wrong and can you please explain in detail so I can understand it, thanks!

your indentation is so ridiculous I'm not even going to try to fix it. please clean up your code block. — Wug
– Wug, Commented Jul 23, 2012 at 21:38
You're trying to use a data_t* as an int*. If you're sure they are the same data type, do a cast. — Hans Z
– Hans Z, Commented Jul 23, 2012 at 21:38

Christian Stieber · Accepted Answer · 2012-07-23 21:41:14Z

1

You don't have an array. An array in C (or C++) would be just a list of integers, and you could pass it like you did.

However, you have a vector (and I'm guessing record_t ends up being an int). vector<>s behave a lot like arrays, but they are not, they are actual objects.

What you probably want to do is write your function as

int sorted(data_t& data, int max_record_size)

and your call simply as

sorted(data,max_record_size);

answered Jul 23, 2012 at 21:41

Christian Stieber

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Comments

bames53 · Accepted Answer · 2012-07-23 21:48:41Z

0

data_t is a vector<vector<double>>. This is not even close to an array of ints. You just need to write a function that handles data_t and not ints.

If the function is supposed to sort data then you should use std::sort, and to do that you'll need to write a comparison function that can compare two elements of data in order to see which one should come before the other in the sorted result.

Here's an example of providing such a comparison function using a lambda with lexicographical_compare.

sort(begin(data),end(data), [](record_t const &lhs,record_t const &rhs) {
    return lexicographical_compare(begin(lhs),end(lhs),begin(rhs),end(rhs));]
});

edited Jul 23, 2012 at 21:48

answered Jul 23, 2012 at 21:41

bames53

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1 Comment

Harper Shelby Over a year ago

Nah, what's needed is a comparison function to pass to std::sort, along with the .begin() and .end() iterators.

Aesthete · Accepted Answer · 2012-07-24 02:26:13Z

0

Try passing a reference to the original vector. Why?

You still want to work with the original vector without making a copy
You can't pass a null reference, so the argument is always valid
You're not doing any pointer arithmetic, so be safe and use a reference
```
int sorted(data_t& data, int max_record_size)
{             
}
```

Pass your data_t structure like this:

sorted(data, max_record_size);

Now you have access to the data_t structure inside your sorted function.

Also

You know that your code is not going to compile?

unsigned max_record_size and int temp[max_record_size] are invalid. If you're going to allocate an array on the stack, you need to use a constant size.
There is no overload on the >> operator in the istream class that handles vector<vector<double>>, so this statement is broken as well: infile >> data;

edited Jul 24, 2012 at 2:26

answered Jul 23, 2012 at 22:07

Aesthete

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4 Comments

Undermine2k Over a year ago

The code complies and reads in the text files and stores it in data. So I can iterate through the entire list but I want to pass a pointer to the vector to a different function. I tried int sorted(vector<int> &data, int max_record_size) but it's giving me errors

Aesthete Over a year ago

You must have an awesome compiler. You can pass your data_t to any function, see my changes.

Undermine2k Over a year ago

thanks that works! can you explain why the function prototype takes data_t& data as a parameter I'm not very clear on this.

Aesthete Over a year ago

You should read more about pointer and references. See my edits to start. I'm glad this solution works for you.

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