MATLAB: Num2str format

formatMATLAB

I have problems with num2str format
I get a number from an API:
8.1784e+17
I need the exact number as str output. For instance I know it is:
'817835078876192769'.
I tried with:
num2str(x,'%u')
however this gives me the following wrong result:
ans =
'817835078876192768'
Anyone have a clue what can be wrong here?

Best Answer

What does "I get a number from an API: 8.1784e+17" mean? Is this a char vector, string or a UINT64 or double scalar? In the last case, remember that doubles contain about 16 digits only. So there is no chance to store a value with 18 digitis accurately.
x = uint64(817835078876192769)
% uint64  817835078876192769
double(x)
%      8.17835078876193e+17
uint64(double(x))
% uint64  817835078876192768
num2str(x)
% '817835078876192769'

sprintf('%d', x)
% '817835078876192769'
sprintf('%.0f', x)
% '817835078876192768'
So the problem might be, that the value is provided as double value. You need to store the value as UINT64 or as char array or string.
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