C++ printing out a decimal value as hex value

Question

I am trying to write an integer decimal value as hex value in C++, but the code below writes the hex value seperated( see the attached image). I want to write it on left and not-seperated. For example if my integer value is 100, its hex value is 0x64 and i want to print out the hex value. Any advise ?

my output

int ia = (int)A;
cout << left << "0x" << setw(sizeof(ia)*2) << hex << uppercase << ia << endl;

I am trying to write an integer value with hex value in C++, but the code below writes the hex value seperated( see the attached image). I want to write it on left and not-seperated.

Please [don't show images of text](https://meta.stackoverflow.com/questions/285551/why-should-i-not-upload-images-of-code-data-errors). Copy-paste text *as text* into your questions. — Some programmer dude, Mar 09 '23 at 10:10
[`std::setfill`](https://en.cppreference.com/w/cpp/io/manip/setfill)? — Alan Birtles, Mar 09 '23 at 10:13
Why are you using the `setw` manipulator? What is the actual output you want, `0x64` or zero-padded like `0x00000064`? Or something else? Please [edit] your question to tell us. — Some programmer dude, Mar 09 '23 at 10:26
Possible duplicate of: https://stackoverflow.com/questions/5100718/integer-to-hex-string-in-c — Oded Ben Dov, Mar 09 '23 at 10:31
If you haven't figured it out yet: Don't use `left` or `setw`. That's all you need to do. Those manipulators are just not needed for this use-case. — Some programmer dude, Mar 10 '23 at 07:29

Jesper Juhl · Answer 1 · 2023-03-29T00:03:45.593

I believe that what you want is something like this:

#include <iostream>
#include <iomanip>
#include <limits>

int main()
{
  int ia = 42;
  const auto save_flags = std::cout.flags();
  std::cout
    << std::left
    << std::showbase
    << std::hex
    << std::uppercase
    << std::setfill('0')
    << std::setw(std::numeric_limits<decltype(ia)>::digits / 4)
    << ia
    << std::endl;
  std::cout.flags(save_flags);
}

This will first of all save the existing flags of the std::cout stream so that you can restore them later after you have manipulated them. Then it will print the number left aligned (std::left) and it will show the base of the number you are printing (0X for hex - this is the std::showbase bit), it will print the number as hex (std::hex) in uppercase (std::uppercase) and it will use 0 to fill any missing digits (std::setfill('0') up to your desired width (which I made the maximum number of digits for the given type - the std::setw(std::numeric_limits<decltype(ia)>::digits / 4) bit). Finally we restore the previous flags of the stream so future prints get the normal (or at least previously set) flags.

C++23

Starting from C++23, you can get rid of iostreams and use the std::print funtion for formatting and printing purposes.

#include <print>
#include <limits>


int main( )
{
    int ia { 42 };

    std::print( "{:0<#{}X}\n", ia,
                std::numeric_limits<decltype( ia )>::digits / 4 );
}

Output:

0X2A000

Explanation: Here in "{:0<#{}X}\n", 0 is the fill character. < is the left alignment symbol. # adds 0X to the beginning of the number. And X is the format specifier for uppercase hex integer formatting.

I want to see from the output "0x64", not "0x640000000". And x will not be upper case, it should be lowercase (0x64 not 0X64). — Eray, Mar 09 '23 at 13:36
@Eray Check this one: [link](https://godbolt.org/z/eqcMPTn8T). — digito_evo, Mar 09 '23 at 17:32

Athir Nuaimi · Answer 2 · 2023-03-09T15:07:09.483

0

A simple way to do this is to use setbase(16) or its equivalent hex.

#include <iostream>
#include<iomanip>

int main() {

    int ia = (int)100;
    std::cout << std::left << "0x" << std::hex << ia << std::endl;

    return 0;
}

edited Mar 09 '23 at 15:07

answered Mar 09 '23 at 10:51

Athir Nuaimi

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`std::setbase(16)` is equivalent to `std::hex`, so the difference to the OP code is dropping `std::setw()`. – nielsen Mar 09 '23 at 11:26
its output is still "0x 64", but i need "0x64". – Eray Mar 09 '23 at 13:38
Not sure why. I get: 0x64. I've updated the sample code to be the complete program. – Athir Nuaimi Mar 09 '23 at 15:07
I've updated the answer to use std:hex rather than std::base(16) as that's what the original question had. thanks for the info Nielsen. – Athir Nuaimi Mar 09 '23 at 15:11

C++ printing out a decimal value as hex value

2 Answers2

C++23