C++ cout Hex values

[patryk77]

Hey,

I am writing a parser for binary data files, and would like to print the Hex values of each char.

I have a pointer, and I assign what it points to to an int.


int hexVal = *ptrStart;

cout.flags(ios::hex);

cout << hexVal << endl;

I tried it with two values, and while I expect A1 and 80, it prints ffffffa1 and ffffff80.

Could anyone tell me why it does that? And how to make it assign and print the correct values?

Thanks

Edit: I guess it must be during the conversion to int that it happens, right?

[monkeyking]

I am in no way an expert but I think you are expecting the hexval of the first byte (8bits),
but cout gives you all 4 bytes (32 bits)(1 int).
you should use chars if you are really only interested in 1 byte.
Futhermore, you should consider using unsigned values, if you are planning to do bit stuff. otherwise your number are in 2-complements

good luck

[patryk77]

Thanks for the reply. I am looking for a single byte value, but I am not sure how to get it.

I actually just tried a short int now, which gives me FFA1. Close but no cigar.

Edit: Meh, no big deal. Will compare with 0xFFA1 for now.

I would still like some input if anyone knows the right way to achieve this, but I need to have it done quick for now.

[eye208]

I would still like some input if anyone knows the right way to achieve this, but I need to have it done quick for now.

cout << (hexVal & 0xFF) << endl;

[the_unforgiven]

You use setf() (http://www.cplusplus.com/reference/iostream/ios_base/setf.html) to set flags and not flags().

[movieman]

you should use chars if you are really only interested in 1 byte.

If you use chars you're likely to get a result you didn't expect :).

Unsigned int and/or (int & 0xff) is the way to go.

[patryk77]

You use setf() (http://www.cplusplus.com/reference/iostream/ios_base/setf.html) to set flags and not flags().

http://www.cplusplus.com/reference/iostream/ios_base/flags.html

flags() works too. Is there a reason for the preference?

Edit 2: Should have read the page first. flags() unsets the other ones. where as setf() just changes specific ones



If you use chars you're likely to get a result you didn't expect :).

Unsigned int and/or (int & 0xff) is the way to go.

Yeah hehe, tried the char method... Printed out garbage.

I'm using unsigned shorts now. Should be good too, right? Edit: they give me the results I expect, even if 0xFFA1 instead of just 0xA1, but I can live with that.


Thanks for the replies :)

[monkeyking]

If you use chars you're likely to get a result you didn't expect :).

Unsigned int and/or (int & 0xff) is the way to go.

If you only need 1byte, then unsigned char is the only choice.
Why should it give strange results?

[soltanis]

int hexVal = *ptrStart;

cout.flags(ios::hex);

cout << hexVal << endl;


Yes. You are using an integer to store the value of a character. Since an integer seems to be 4 bytes on your system, the extra 3 bytes are being printed. Use an unsigned char instead.

[patryk77]

Unsigned char also prints garbage.

Will stick to unsigned short, I guess.

[the_unforgiven]

This following code seems to be working for me:


#include <iostream>

int main()
{
int hexVal = 0xa1;
std::cout.setf(std::ios::hex, std::ios::basefield);
std::cout.setf(std::ios::showbase);
std::cout << hexVal << std::endl;
return 0;
}

Note that I'm using a plain int and it still prints '0xa1' for me.

[eye208]

Note that I'm using a plain int and it still prints '0xa1' for me.
Chars are signed by default. If you convert char 0xA1 to signed int, the result is not 0x000000A1 (161) but 0xFFFFFFA1 (-95).

[geirha]

int hexVal = *ptrStart;

cout.flags(ios::hex);

cout << hexVal << endl;


If you give cout an unsigned char, it will print it as a char. But if you give it an int, it will print it as a number.


unsigned char hexVal = *ptrStart;
cout << showbase << hex << (int)hexVal << endl;

[patryk77]

If you give cout an unsigned char, it will print it as a char. But if you give it an int, it will print it as a number.


unsigned char hexVal = *ptrStart;
cout << showbase << hex << (int)hexVal << endl;


Awesome! Thanks :)

This works, and comparing it to 0xA1 works :)