Wrong print negative number with fprintf in hex

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vadim onuchin
vadim onuchin 2021-5-4
评论： Walter Roberson 2024-3-15
Why can't print function fprintf negative values in hex?
For example:
rng(73);
N = 20;
r = (randn(N, 1) + 1j.*randn(N, 1)) * 10000;
for i = 1:N
fprintf('Real[%d] = %04X; ', i, int16(real(r(i))));
fprintf('Imag[%d] = %04X; \n', i, int16(imag(r(i))));
end
And result:
Real[1] = 0D6C; Imag[1] = 1DF2;
Real[2] = 053A; Imag[2] = -1.007700e+04;
Real[3] = 00E1; Imag[3] = -1.237000e+04;
Real[4] = 0D85; Imag[4] = 0435;
Real[5] = -1.700000e+02; Imag[5] = -1.814200e+04;
Real[6] = -4.073000e+03; Imag[6] = -5.949000e+03;
Real[7] = -1.211600e+04; Imag[7] = -1.676000e+04;
Real[8] = 0875; Imag[8] = -5.985000e+03;
Real[9] = 3021; Imag[9] = 19A0;
Real[10] = -1.096100e+04; Imag[10] = 378C;
Real[11] = -3.266000e+03; Imag[11] = 20AB;
Real[12] = 0B82; Imag[12] = 167C;
Real[13] = -1.231200e+04; Imag[13] = -1.007300e+04;
Real[14] = 270D; Imag[14] = 091E;
Real[15] = -1.406600e+04; Imag[15] = 13FC;
Real[16] = 056C; Imag[16] = 0E25;
Real[17] = -6.861000e+03; Imag[17] = -1.780700e+04;
Real[18] = 1EE4; Imag[18] = -6.337000e+03;
Real[19] = 1EF1; Imag[19] = 01D4;
Real[20] = -1.694700e+04; Imag[20] = -8.530000e+02;
May be some cast need before?

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采纳的回答

Walter Roberson
Walter Roberson 2024-3-15
Ran in:
rng(73);
N = 20;
r = (randn(N, 1) + 1j.*randn(N, 1)) * 10000;
for i = 1:N
fprintf('Real[%d] = %04X; ', i, typecast(int16(real(r(i))), 'uint16')); fprintf('Imag[%d] = %04X; \n', i, typecast(int16(imag(r(i))), 'uint16'));
end
Real[1] = 0D6C; Imag[1] = 1DF2; Real[2] = 053A; Imag[2] = D8A3; Real[3] = 00E1; Imag[3] = CFAE; Real[4] = 0D85; Imag[4] = 0435; Real[5] = FF56; Imag[5] = B922; Real[6] = F017; Imag[6] = E8C3; Real[7] = D0AC; Imag[7] = BE88; Real[8] = 0875; Imag[8] = E89F; Real[9] = 3021; Imag[9] = 19A0; Real[10] = D52F; Imag[10] = 378C; Real[11] = F33E; Imag[11] = 20AB; Real[12] = 0B82; Imag[12] = 167C; Real[13] = CFE8; Imag[13] = D8A7; Real[14] = 270D; Imag[14] = 091E; Real[15] = C90E; Imag[15] = 13FC; Real[16] = 056C; Imag[16] = 0E25; Real[17] = E533; Imag[17] = BA71; Real[18] = 1EE4; Imag[18] = E73F; Real[19] = 1EF1; Imag[19] = 01D4; Real[20] = BDCD; Imag[20] = FCAB;
  2 个评论
vadim onuchin
vadim onuchin 2024-3-15
编辑：vadim onuchin 2024-3-15
yes, in newer version it's working. but in matlab r2019b not working.
It's bug in matlab r2019b.
Walter Roberson
Walter Roberson 2024-3-15
I installed and tested R2019b. Given the above code, it produces exactly the same output as abover.
It is not a bug that %x does not handle negative values; %x only handles positive values. Using typecast() as I show here works

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更多回答（1 个）

Swastik Sarkar
Swastik Sarkar 2024-3-4
Ran in:
Hi Vadim,
I understand that you want to print negative hexadecimal number, also I assume the 2’s complement of the negative number’s absolute value is to be printed in hex. So, -1 would print as 0xFFFF according to this.
I found that fprintf in MATLAB does not print negative numbers with the hexadecimal format(%x), this is mentioned in the documentation of fprintf which reads:
“If you specify a conversion that does not fit the data, such as a text conversion for a numeric value, MATLAB overrides the specified conversion, and uses %e.”
Here is the link for the same:
https://www.mathworks.com/help/releases/R2019b/matlab/ref/fprintf.html#btf8xsy-1_sep_shared-formatSpec
In this case, MATLAB expects an unsigned integer to the format specifier “%x”, however does not find one and defaults to “%e”.
I would like to suggest the following workaround to print the hexadecimal representation of a negative number,
If a is a signed integer, then we can apply the following operation to make sure it prints in hexadecimal every time.
a = -1
a = -1
fprintf("%04x", a + (a<0)*2^32)
ffffffff
Hope this helps.

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