MATLAB: Fwrite to fread changes data completely!

datadlmwritedoublefclosefloatfopenfreadfwriteprecisionsave

Hello Friends,

I have a Vector or some length, say, 1 x N with real number entries.

I want to save this vector by using "fwrite" and then read it using "fread". I did the following:

fileID = fopen(Name, 'w');
fwrite(fileID, Vector, 'double', [number_of_rows number_of_columns]);
%Here [number_of rows number_of_cols] = size(Vector);
fclose(fileID);

In workspace, Vector shows of type 'double'

Next, for reading it, I did the following:

      fid = fopen(path_to_vector, 'r');
      output = fread(fid, [1 length_of_vector], 'double');
      fclose(fid);

However, the "output" shows completely different values than what I saved using "fwrite". I tried to change precision from double to type float, int, etc., but it does not work. How can I get exactly the same vector what I saved?

I will appreciate any advise!

Best Answer

This works for me on R2016a,Win7,64b. (Replacing real*8 by double doesn't change that.)

>> cssm( rand(1,1000) )
ans =
     1

where

function  ok = cssm( vec )
    fid = fopen( 'cssm.bin', 'w' );
    fwrite( fid, vec, 'real*8' );
    fclose( fid );
    fid = fopen( 'cssm.bin', 'r' );
    out = fread( fid, size(vec), 'real*8' );
    fclose( fid );
    ok = all(vec==out);
end

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MATLAB: Copy a line from a txt to other txt

Hi!

count = 1;
tline = fgetl(fid01);
while ischar(tline)
count = count + 1;
disp(tline)
if count == 3
fprintf(fid02,'%s\r\n',tline);
end
tline = fgetl(fid01);
end 
fclose(fid01);
fclose(fid02);

You can do as well

for n = 1:3
tline = fgetl(fid01);
end
fprintf(fid02,'%s\r\n',tline);
fclose(fid01);
fclose(fid02);

MATLAB: Does csvread behave differently for large csv files

I reproduced your result on R2013a, Win7

>> [CR,FS] = cssm(1e5); whos('CR','FS')
  Name           Size             Bytes  Class     Attributes
  CR        100000x1             800000  double              
  FS        100000x1             800000  double              
>> [CR,FS] = cssm(1e3); whos('CR','FS')
  Name         Size              Bytes  Class     Attributes
  CR           1x1001             8008  double              
  FS        1000x1                8000  double

where

function    [ CR, FS ] = cssm( N )
    str = repmat( '1.1,', 1, N );
    fid = fopen( 'cssm.txt', 'w' );
    fprintf( fid, '%s', str );
    fclose( fid );
    CR  = csvread( 'cssm.txt' );
    fid = fopen( 'cssm.txt', 'r' );
    FS  = fscanf( fid, '%f,' );
    fclose( fid );
end

"As I understand it, csvread should produce a row matrix with an extra 0" &nbsp I didn't find that stated in in the documentation of csvread

csvread is based on textscan and contains a bit of automagic. I guess, it was never intended for rows that long, i.e. files without new lines.

&nbsp

without the ending comma

And without the ending comma, cvsread returns a row for the large file.

>> [CR,FS] = cssm(1e5); whos('CR','FS')
  Name           Size                 Bytes  Class     Attributes
  CR             1x100000            800000  double              
  FS        100000x1                 800000  double

&nbsp

textscan with empty formatSpec

csvread calls textscan with formatSpec set to an empty string. That option of textscan is not documented. It makes a difference in this special case.

>> [CR,FS,TS1,TS2] = cssm(1e3); whos('CR','FS','TS1','TS2')
  Name         Size              Bytes  Class     Attributes
  CR           1x1001             8008  double              
  FS        1000x1                8000  double              
  TS1       1000x1                8000  double              
  TS2          1x1001             8008  double              
>> [CR,FS,TS1,TS2] = cssm(1e5); whos('CR','FS','TS1','TS2')
  Name           Size             Bytes  Class     Attributes
  CR        100000x1             800000  double              
  FS        100000x1             800000  double              
  TS1       100000x1             800000  double              
  TS2       100000x1             800000  double

where

function    [ CR, FS, TS1, TS2 ] = cssm( N )
    str = repmat( '1.1,', 1, N );
    fid = fopen( 'cssm.txt', 'w' );
    fprintf( fid, '%s', str(1:end) );
    fclose( fid );
    CR  = csvread( 'cssm.txt' );
    fid = fopen( 'cssm.txt', 'r' );
    FS  = fscanf( fid, '%f,' );
    fclose( fid );
    fid = fopen( 'cssm.txt', 'r' );
    cac = textscan( fid, '%f', 'Delimiter',','            ... 
                  , 'CollectOutput',true, 'EmptyValue',999 );
    fclose( fid );
    TS1 = cac{:};
    fid = fopen( 'cssm.txt', 'r' );
    cac  = textscan( fid, '', 'Delimiter',','               ...
                   , 'CollectOutput',true, 'EmptyValue',999 );
    fclose( fid );
    TS2 = cac{:};
end

&nbsp

For the large file, all of the functions and options I tested fails to recognize the ending comma.

Best Answer

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