[Octave-bug-tracker] [bug #45687] fread does not allow different ARCH when file fopen'd with ARCH

[Emmanuel Goua de Baix]

Follow-up Comment #8, bug #45687 (project octave):

Rik, your results with the corrected version seem OK for me.
Here are the results when displaying the values (same as yours except that
obviously I still get the error for b/ieee-le since I made no change to my
Octave):


Octave V4.0.0
fopen ARCH nothing | fread ARCH nothing => OK
fopen ARCH ieee-le | fread ARCH nothing => ans =   2.1787e+005
fopen ARCH ieee-be | fread ARCH nothing => ans =   2.7444e-307
fopen ARCH       b | fread ARCH nothing => ans =   2.7444e-307
fopen ARCH nothing | fread ARCH  native => ans =   2.1787e+005
fopen ARCH ieee-le | fread ARCH  native => ans =   2.1787e+005
fopen ARCH ieee-be | fread ARCH  native => ERROR !
fopen ARCH       b | fread ARCH  native => ERROR !
fopen ARCH nothing | fread ARCH ieee-be => ans =   2.7444e-307
fopen ARCH ieee-le | fread ARCH ieee-be => ans =   2.7444e-307
fopen ARCH ieee-be | fread ARCH ieee-be => ans =   2.7444e-307
fopen ARCH       b | fread ARCH ieee-be => ans =   2.7444e-307
fopen ARCH nothing | fread ARCH ieee-le => ans =   2.1787e+005
fopen ARCH ieee-le | fread ARCH ieee-le => ans =   2.1787e+005
fopen ARCH ieee-be | fread ARCH ieee-le => ERROR !
fopen ARCH       b | fread ARCH ieee-le => ERROR !

ML 2010a (reformatted for better reading)
fopen ARCH nothing | fread ARCH nothing => OK
fopen ARCH ieee-le | fread ARCH nothing => ans =  2.1787e+005
fopen ARCH ieee-be | fread ARCH nothing => ans =  2.7444e-307
fopen ARCH       b | fread ARCH nothing => ans =  2.7444e-307
fopen ARCH nothing | fread ARCH  native => ans =  2.1787e+005
fopen ARCH ieee-le | fread ARCH  native => ans =  2.1787e+005
fopen ARCH ieee-be | fread ARCH  native => ans =  2.1787e+005
fopen ARCH       b | fread ARCH  native => ans =  2.1787e+005
fopen ARCH nothing | fread ARCH ieee-be => ans =  2.7444e-307
fopen ARCH ieee-le | fread ARCH ieee-be => ans =  2.7444e-307
fopen ARCH ieee-be | fread ARCH ieee-be => ans =  2.7444e-307
fopen ARCH       b | fread ARCH ieee-be => ans =  2.7444e-307
fopen ARCH nothing | fread ARCH ieee-le => ans =  2.1787e+005
fopen ARCH ieee-le | fread ARCH ieee-le => ans =  2.1787e+005
fopen ARCH ieee-be | fread ARCH ieee-le => ans =  2.1787e+005
fopen ARCH       b | fread ARCH ieee-le => ans =  2.1787e+005


Now that I think of it, the results b/nothing are unexpected: it behaves like
b/ieee-be instead of b/native.
The documentation of Octave about fread() is silent about the default value
but the documentation of ML states that 'native' is the default ARCH. Still in
fread()'s doc, I think there is no reference about the ARCH used by fopen().
No reference about ARCH used by fread() neither in fopen().

So I feel like the implementation of fread() uses the ARCH of fopen() by
default, not necessarly 'native'. The documentation of ML is wrong on this
point.

I discovered this issue with a binary file written by a C program where int
are big-endian and float are little-endian.
One can also imagine a file where some floats are LE and some others are BE
(headaches granted !).
I think that the feature to let the programmer force the ARCH in fread()
independantly to the one used by fopen() is good and shall remain IMHO.


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