C++ cout hex values? | 易学教程

问题

I want to do:

int a = 255; 
cout << a;

and have it show FF in the output, how would I do this?

回答1:

Use:

#include <iostream>

...

std::cout << std::hex << a;

There are many other options to control the exact formatting of the output number, such as leading zeros and upper/lower case.

回答2:

std::hex is defined in <ios> which is included by <iostream>. But to use things like std::setprecision/std::setw/std::setfill/etc you have to include <iomanip>.

回答3:

To manipulate the stream to print in hexadecimal use the hex manipulator:

cout << hex << a;

By default the hexadecimal characters are output in lowercase. To change it to uppercase use the uppercase manipulator:

cout << hex << uppercase << a;

To later change the output back to lowercase, use the nouppercase manipulator:

cout << nouppercase << b;

回答4:

If you want to print a single hex number, and then revert back to decimal you can use this:

std::cout << std::hex << num << std::dec << std::endl;

回答5:

There are different kinds of flags & masks you can use as well. Please refer http://www.cplusplus.com/reference/iostream/ios_base/setf/ for more information.

#include <iostream>
using namespace std;

int main()
{
    int num = 255;
    cout.setf(ios::hex, ios::basefield);
    cout << "Hex: " << num << endl;

    cout.unsetf(ios::hex);
    cout << "Original format: " << num << endl;

    return 0;
}

回答6:

I understand this isn't what OP asked for, but I still think it is worth to point out how to do it with printf. I almost always prefer using it over std::cout (even with no previous C background).

printf("%.2X", a);

'2' defines the precision, 'X' or 'x' defines case.

回答7:

std::hex gets you the hex formatting, but it is a stateful option, meaning you need to save and restore state or it will impact all future output.

Naively switching back to std::dec is only good if that's where the flags were before, which may not be the case, particularly if you're writing a library.

#include <iostream>
#include <ios>

...

std::ios_base::fmtflags f( cout.flags() );  // save flags state
std::cout << std::hex << a;
cout.flags( f );  // restore flags state

This combines Greg Hewgill's answer and info from another question.

来源：https://stackoverflow.com/questions/479373/c-cout-hex-values

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