How to read 8-byte floating point numbers from binary?use fread
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aijiangzhao aixuwu
am 28 Okt. 2021
Bearbeitet: Jan
am 12 Nov. 2021
fseek(fid,56,'bof');
x = fread(fid,1,'float64','b')
3 Kommentare
Walter Roberson
am 29 Okt. 2021
When you fopen you should specify the byte order as the third parameter to fopen, unless you are reading from something with mixed orders.
If you are reading from something with mixed orders but know the order for one particular binary fread then specify the byte order as a parameter to fread.
If you are reading a sequence of bytes at one time and regrouping them (such as if you were reading a structure with mixed datatype) then if necessary use swapbytes after any necessary typecast()
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Jan
am 30 Okt. 2021
Bearbeitet: Jan
am 12 Nov. 2021
With 'ieee-le' format the bytes are read in the order [8,7,6,5,4,3,2,1], with 'ieee-be' as [1,2,3,4,5,6,7,8]. There is no format to store doubles with the byte order [4,3,2,1,8,7,6,5]. Yo you have to convert the order manually by reading the bytes, mix them as wanted and use typecast for the conversion.
[EDITED] As code:
bytes = fread(fid, 8, '*uint8');
bytes = bytes([4,3,2,1,8,7,6,5]);
value = typecast(bytes, 'double')
8 Kommentare
Jan
am 12 Nov. 2021
As I have suggested already, except for the changed byte order:
% fseek(fid, 56, 'bof');
% bytes = fread(fid, 8, '*uint8');
% Manually:
bytes = uint8(sscanf('C5 B9 FB 60 C1 4B FD CA', '%x')).';
value = typecast(fliplr(bytes), 'double') % As your fread('float64')
% [197, 185, 251, 96, 193, 75, 253, 202]
bytes = bytes([4,3,2,1,8,7,6,5]);
value = typecast(bytes, 'double')
Now the byte order and the order of 4-Byte-blocks is swapped.
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