how to output the hex data back from input file

Question

How to store a file to unsigned int

#include <iostream>
#include <fstream>

using namespace std;

unsigned int key[4];

int main(){
    ifstream file("key.txt");
    store(file);
    return 0;
}

I have this data in my key.txt

0xFDA5
0xD54E
0xFC00
0xB55A

I created this function

void store(ifstream &file){
    int i = 0;
    if(!file)
        cout << "Couldn't open file " << endl;

    while(!file.eof()){

         file >> hex >> key[i];
         i++;
    }

    for( int i = 0 ; i < 4 ; i++ ){
          cout << k[i] << endl;
    }
}

I get the number is in hex value . My question is if I want to get back this output

0xFDA5
0xD54E
0xFC00
0xB55A

which code should I use?

Answer 1

For uppercase output (e.g. 0XFDA5) edit the for loop as follows:

for( int i = 0; i < 4; i++ ) {
      cout << std::uppercase << showbase << std::hex << key[i] << endl;
}

or

for( int i = 0; i < 4; i++ ){
       printf("%#X\n", key[i]);
}

For lowercase output(e.g. 0xfda5) edit the for loop as follows:

for( int i = 0; i < 4; i++ ) {
      cout <<  showbase << std::hex << key[i] << endl;
}

or

for( int i = 0; i < 4; i++ ){
       printf("%#x\n", key[i]);
}

Answer 2

As said before, std::hex for hexadecimal, std::showbase for the 'Ox' prefix and std::uppercase for the uppercase.

But what about simply using the STL instead of the for loop :

#include <algorithm>
#include <iostream>
#include <fstream>
#include <iterator>

int main()
{
    std::ifstream file("key.txt");

    copy(
        std::istream_iterator<unsigned int>(file>>std::hex)
        ,std::istream_iterator<unsigned int>()
        ,std::ostream_iterator<unsigned int>(std::cout<<std::hex<<std::uppercase<<std::showbase,"\n")
    );

    return 0;
}

Even if you need a variable to store items :

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

int main()
{
    std::ifstream file("key.txt");

    std::vector<unsigned int> keys;
    keys.reserve(4);

    copy(
        std::istream_iterator<unsigned int>(file>>std::hex)
        ,std::istream_iterator<unsigned int>()
        ,back_inserter(keys)
    );

    copy(
        begin(keys)
        ,end(keys)
        ,std::ostream_iterator<unsigned int>(std::cout<<std::hex<<std::uppercase<<std::showbase,"\n")
    );

    return 0;
}