num2str format

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?

Answer 1

[Jan]

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.

[Martin]

Its a double scalar yes. So there is nothing to be done in this case you think?

[Jan]

It depends on what "from API" means. From which API?