readtable interpretes time hh:mm:ss:SSS in different ways

Matlab R2020a:

For reading a text file I use:

    buffer = fread(fid, Inf);
    fclose(fid);
    fid = fopen('BufferFile.txt', 'w');
    fwrite(fid, buffer); 
    R = readtable('BufferFile.txt', "FileType", "text");
    fclose(fid);

For BufferFile.txt = A

R will show the seconds with fractional part, see column 2,

for BufferFile.txt = B (containing the seconds with fractionals in the same way)

R shows the seconds as int.

How can I make them to int in both cases?

Answer 1

[Jan]

I do not understand the meaning of your file operations. As far as I understand, the problem can be reproduced by:

RA = readtable('A_BufferFile.txt', "FileType", "text");
RB = readtable('B_BufferFile.txt', "FileType", "text");

Correct?

Now I get in R2018b:

RA(1:3, :)
  3×15 table
         x_             GPST        latitude_deg_    longitude_deg_    height_m_  
    ____________    ____________    _____________    ______________    _________  
    '2021/03/09'    16:43:20.000    49.486501109      11.128521899     393.4746   
    '2021/03/09'    16:43:21.000    49.486500611      11.128522695     393.4638   
    '2021/03/09'    16:43:22.000    49.486500796      11.128523451     393.4387   
%                            ^^^
    
RB(1:3, :)
  3×15 table
         x_           GPST      latitude_deg_    longitude_deg_    height_m_
    ____________    ________    _____________    ______________    _________
    '2021/03/08'    15:00:46     49.48639163      11.128834329     387.0342 
    '2021/03/08'    15:00:47    49.486350345      11.128823205     389.2862 
    '2021/03/08'    15:00:48    49.486346769      11.128809793     391.7787 

The different display comes from fractional parts in RA.GPST, e.g.:

16:53:51.001
17:05:40.001
17:05:41.001

This let readtable modify the Format of the duration automagically:

RA.GPST.Format   % 'hh:mm:ss.SSS'
RB.GPST.Format   % 'hh:mm:ss'

You can round this and/or modify the format:

RA.GPST = round(RA.GPST)
RA.GPST.Format = 'hh:mm:ss'

Note: This is fragile:

fid = fopen('BufferFile.txt', 'w');
fwrite(fid, buffer); 
R = readtable('BufferFile.txt', "FileType", "text");
fclose(fid);

Reading from a file, which is open for writing might work, but this is not guaranteed. Close the file before reading it to flush the buffer.

[Walter Roberson]

fseek() on the file to flush it. Even if you fseek() 0 bytes relative to the current position.

[Barbara Kreh]

This was easy and helped. Thank you, Jan!

[Jan]

@Walter Roberson: 15 years ago I had trouble with FSEEK on a Linux machine. On very heavy load the operation was not successful. It was a timing problem and I've found some sources, which explains, why the underlying C function fails, when a "thread switch" occurs. At least the replies status was -1 in this cases. After a failed fseek(FID, x, 0) it was impossible to obtain the current position, so fseek(fid, ftell(fid) + 1, -1) was the stable solution.

In Matlab 6.5 opening a file twice changed the read/write access for the other file handle also. This has been changed later, but I decided to reduce the risk of bugs by closing files before they are accessed elesewhere.

Does fseek() flush reliably today even if the file was opened in 'W' or 'A' mode (uppercase)? Is this documented?