Hex printf is limited to 8 Fs

Bryan Kelly

I am working on a long divide app and trying to see the complete value in hex. Here is the critical source.

    uint64_t dividend;
    dividend    = 0XFFFFFFFF;  // count is 9 Fs
    printf( "with 8 Fs dividend is     %llu, in hex %#020X \n", dividend, dividend );

    dividend    = 0XFFFFFFFFF;  // count is 9 Fs
    printf( "with 9 Fs dividend is    %llu, in hex %#020X \n", dividend, dividend );

    dividend    = 0XFFFFFFFFFF;  // count is 10 Fs
    printf( "with 10 Fs dividend is %llu, in hex %#020X \n", dividend, dividend );
    printf( "\n");

and here is the output

with 8 Fs dividend is     4294967295, in hex 0X0000000000FFFFFFFF
with 9 Fs dividend is    68719476735, in hex 0X0000000000FFFFFFFF
with 10 Fs dividend is 1099511627775, in hex 0X0000000000FFFFFFFF

A 64-bit number is 8 bytes. At 2 hex characters per byte that is 16 Fs. The printf output is limited to 8 Fs.
What is wrong with my printf statement?

Christian Ehrlicher

@Bryan-Kelly said in Hex printf is limited to 8 Fs:

dividend = 0XFFFFFFFFFF; // count is 10 Fs

You are wrong. See https://en.cppreference.com/w/cpp/language/integer_literal

Don't know what this has to do with Qt though.

Bryan Kelly

Ok, and yes I am wrong. But please be a bit more precise. That page does not use items from stdint.h and does not use printf.
What does this have to do with Qt? Because that is what I am using and I don't see an error in my code.
And maybe it matters to state I am using a console app.

Christian Ehrlicher

Your problem is plain c. As the site tells you a number is by default an integer (32 bit) when you don't add a proper suffix.

andr

Try %#020lX as format. Note the 'l'.

Christian Ehrlicher

This post is deleted!

Christian Ehrlicher

@andr said in Hex printf is limited to 8 Fs:

Try %#020lX as format. Note the 'l'.

That's correct. I was stuck in old times. The suffix for big numbers is still useful though when using the 'auto' keyword 🙂.
So sorry, the correct link is https://cplusplus.com/reference/cstdio/printf/

Bryan Kelly

As I read it, you added a character for l, lower case L, in front of the X. When I changed the code it made no difference. I tried the character 1, digit 1, and it made the zero count to be 201, but still ended with 8 Fs, not 9 or 10.

    uint64_t dividend;
    dividend    = 0XFFFFFFFF;  // count is 9 Fs
#ifdef SHOW_DETAILS
    printf( "with 8 Fs dividend is     %llu, in hex %#020X \n", dividend, dividend );
#endif

// changed the below adding character 1, one, made the output 201 characters
    dividend    = 0XFFFFFFFFF;  // count is 9 Fs
#ifdef SHOW_DETAILS
    printf( "with 9 Fs dividend is    %llu, in hex %#0201X \n", dividend, dividend );
#endif
    dividend    = 0XFFFFFFFFFF;  // count is 10 Fs

// change below adding lower case letter L, no detecable difference.
#ifdef SHOW_DETAILS
    printf( "with. 10 Fs dividend is %llu, in hex %#020lX \n", dividend, dividend );
    printf( "\n");
#endif

Bryan Kelly

MS Bing came up with the suggestion. It adds some includes

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>

and the new line

printf( "LINE %4i with 16 Fs dividend is %llu, in hex 0X%" PRIX64 "\n", __LINE__, dividend, dividend );

and the output

LINE   51 with 16 Fs dividend is 18446744073709551615, in hex 0XFFFFFFFFFFFFFFFF