how can i save the full timestamp ID number?

hi guys

i have some data which i fetch from device that samples freq, volt and power. each time i recieve a sample, ill give it a datenum ID using the matlab function "now". Then ill save the data into a .txt file. The problem is, that when i save the data, the datenum ID numbers are cuttoff, making all of them the same number. That means that when i load the data again, all of the samples has the same datenum ID number, which makes it impossible to plot the data?

here is an example of what my .txt file might look like. the 4. collumn contains the timestamp ID numbers.

 49886 2.361440e+004 1.339829e+003 7.348937e+005 
 49886 2.361004e+004 1.339829e+003 7.348937e+005 
 49897 2.358127e+004 1.337393e+003 7.348937e+005 
 49921 2.360107e+004 1.337393e+003 7.348937e+005 
 49928 2.359396e+004 1.337393e+003 7.348937e+005 
 49931 2.357588e+004 1.337393e+003 7.348937e+005 
 49938 2.356435e+004 1.334957e+003 7.348937e+005

Does anybody know how i can save the full timestamp ID number?

[Dr. Seis]

Can you post the code you use to save the data to the text file?

[Adam]

Yes, here it is:

function SaveData(data)

%first collumn of 'data' is freq

%second collumn of 'data' is voltage

%third collumn of 'data' is power

%fourth collumn of 'data' is datenum ID

[filename, filepath] = uiputfile()

fid = fopen(filename,'w');

fprintf(fid,'%6u %6u %6u 6u\n',data);

fclose(fid);

Answer 1

[Walter Roberson]

If you use dlmwrite() then you can use the Precision argument to specify a format to write with, such as '%.16e'

Answer 2

[Walter Roberson]

You missed the '%' before the final 6u.

The %u format is for unsigned integers (in base 10.) When you use it to output a number which is not sufficiently close to an integer, then according to the fprintf() documentation,

If you specify a conversion that does not fit the data, such as a string conversion for a numeric value, MATLAB overrides the specified conversion, and uses %e.

It appears to me that a %.9f format would be consistent with the values for now() that are printed if you have

format long g

in effect. However, as best I calculate at the moment, millisecond resolution can be achieved with %.8f format.

[Adam]

okay thx. i will try this tomorrow.

I am using now() in another function called readData(), in which i am also saving the data and the numdate ID into the array with the name 'data'. Should i put the line "format long g", in readData() or in SaveData() ?