You are looking for the chr function.

You seem to be mixing decimal representations of integers and hex representations of integers, so it's not entirely clear what you need. Based on the description you gave, I think one of these snippets shows what you want.

>>> chr(0x65) == '\x65'
True


>>> hex(65)
'0x41'
>>> chr(65) == '\x41'
True

Note that this is quite different from a string containing an integer as hex. If that is what you want, use the hex builtin.

Since hex is a Integer literal, you can ask the fmt package for a string representation of that integer, using fmt.Sprintf(), and the %x or %X format.
See playground

i := 255
h := fmt.Sprintf("%x", i)
fmt.Printf("Hex conv of '%d' is '%s'\n", i, h)
h = fmt.Sprintf("%X", i)
fmt.Printf("HEX conv of '%d' is '%s'\n", i, h)

Output:

Hex conv of '255' is 'ff'
HEX conv of '255' is 'FF'

// Store integer 182
int intValue = 182;
// Convert integer 182 as a hex in a string variable
string hexValue = intValue.ToString("X");
// Convert the hex string back to the number
int intAgain = int.Parse(hexValue, System.Globalization.NumberStyles.HexNumber);

from http://www.geekpedia.com/KB8_How-do-I-convert-from-decimal-to-hex-and-hex-to-decimal.html

HINT (from the comments):

Use .ToString("X4") to get exactly 4 digits with leading 0, or .ToString("x4") for lowercase hex numbers (likewise for more digits).

This code

int a = 5;
printf("%x\n", a);

prints

5

This code

int a = 5; 
printf("0x%x\n", a);

prints

0x5

This code

int a = 89778116;
printf("%x\n", a);

prints

559e7c4

If you capitalize the x in the format it capitalizes the hex value:

int a = 89778116;
printf("%X\n", a);

prints

559E7C4

If you want to print pointers you use the p format specifier:

char* str = "foo";
printf("0x%p\n", str);

prints

0x01275744

Documentation says Integer.toHexString returns the hexadecimal representation of the int as an unsigned value.

I believe Integer.toString(value, 16) will accomplish what you want.

This answer is for C++17 and earlier. For C++20 and later, see next answer: https://stackoverflow.com/a/69326849/1332468

Use <iomanip>'s std::hex. If you print, just send it to std::cout, if not, then use std::stringstream

std::stringstream stream;
stream << std::hex << your_int;
std::string result( stream.str() );

You can prepend the first << with << "0x" or whatever you like if you wish.

Other manips of interest are std::oct (octal) and std::dec (back to decimal).

One problem you may encounter is the fact that this produces the exact amount of digits needed to represent it. You may use setfill and setw this to circumvent the problem:

stream << std::setfill ('0') << std::setw(sizeof(your_type)*2) 
       << std::hex << your_int;

So finally, I'd suggest such a function:

template< typename T >
std::string int_to_hex( T i )
{
  std::stringstream stream;
  stream << "0x" 
         << std::setfill ('0') << std::setw(sizeof(T)*2) 
         << std::hex << i;
  return stream.str();
}