What is the difference between fopen( 'r'),fopen('r','b') ?

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subha 2014-6-30

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评论： subha 2014-7-3

When i try to open a file in different way, i get different ans. what it represent? As per my understanding from documents, 'b' represent machine format. b represets bigendian format. By default it will take little indian format. so second one takes little endian format. When i go through about big and little indian, it is memory representation format. what is the difference between the values in 1 and 2.

1. fid = fopen('train-images-idx3-ubyte', 'r', 'b')

header = fread(fid, 1, 'int32')

header =

2051

2. fid = fopen('train-images-idx3-ubyte', 'r')

header = fread(fid, 1, 'int32')

header =

50855936

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Philip Borghesani 2014-7-1

Just be careful 'rb' in MATLAB is not the same as 'rb' in C. In C on Windows b means binary mode which is the default in MATLAB, to get text mode fopen (the default in C on Windows) use rt in MATLAB.

C has no equivalent to the machine format options in MATLAB.

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Answer 1

dpb 2014-6-30

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编辑：dpb 2014-7-1

在 MATLAB Online 中打开

Storage order in memory of which byte in memory is the most/least significant. See the following link for details...

http://people.cs.umass.edu/~verts/cs32/endian.html

ADDENDUM

That, of course, is for the syntax of your case 1) which, I now note is NOT the same as that of the subject line of the question;, ie,

fid=fopen(filename,'r','b');

is nothing at all like

fid=fopen(filename,'rb');

--the two 'b' 's are entirely different animals owing to position. In the former, it's the optional third argument in the syntax

[FID, MESSAGE] = fopen(FILENAME,PERMISSION,MACHINEFORMAT);

so it's the MACHINEFORMAT parameter, in the latter it's the second (also optional) argument as in

[FID, MESSAGE] = fopen(FILENAME,PERMISSION)

so it's part of the PERMISSIONs string in which case it is, as Philip notes, indicating a stream ('binary') file format as opposed to ASCII ('text') as given by the 't' substring.

Again, see

doc fopen

and read all the supplementary description for the various parameters for the details. The short story is that the 't' indicates text mode that forces the cr/lf pair for \n on Windows that is superfluous in Unix-like OS platforms.