Thread: Arrays and Functions

I know that you can't directly return an array from a function, but I'm a little shaky on how to use pointers with arrays.

I've tried using a function like this to read data from a file and assign it to an array via a function:

Code:

ifstream fin;
char array[4];
void readText(char *array)
{  
     for(int i=0;i==sizeof array;i++)
             *(array+i)=fin.get();
}

The .dat file is simply

Code:

TEST

When I use cout to display the contents of the array that should have received the data from the file, I only receive 4 blank spaces. Apparently nothing is being written to the array, but I don't really understand what exactly is going on.

Your problem is less about pointers and more about for loops, in that sizeof array is not zero and therefore the for loop never happens.

However: the dimensions of an array do not get passed in to a function -- hence sizeof array is the sizeof any pointer on your system, usually four. You will need to pass in the dimensions separately using another parameter to your function.

Alternatively, you could use a std::vector<char> to save the data into instead of an array.

Code:

#include <vector>
#include <iostream>
#include <fstream>
#include <iterator>

int main(void)
{
    std::ifstream input("testfile.dat");

    std::vector<char> v((std::istream_iterator<char>(input)),
            std::istream_iterator<char>());

    copy(v.begin(), v.end(), std::ostream_iterator<char>(std::cout));
    std::cout << std::endl;
}

Thanks for the help. I managed to get everything sorted out.

One last question:

Is there a specific function that can return the size, in bytes, of a data file? I've searched around a bit, but I haven't been able to find anything.

Thanks

The only cross platform way is to open the file and read all the data to get the total size in bytes.

>> The only cross platform way is to open the file and read all the data to get the total size in bytes.

That might be the only completely portable way, but I believe cross-platform libraries have this ability (such as boost's filesystem).