How to binary clone a file using fread and fwrite commands

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TripleSSSS
TripleSSSS on 22 Jul 2020
Answered: Walter Roberson on 23 Jul 2020
Hey there
I'd like to edit a binary file in a certain locaiton in the file, however before I start I'd like to clone a file using fread and fwrite commands.
I wrote a script that does that in matlab, I use the fread and fwrite commands with binary flag.
I compare the source and desitnation files with beyhond comapre - the files are not identical.
What am I doing wrong here? I simply read and write the same charecter.
you can simply using a random binary file for this example
regards
S
%%
clearvars;
% binary open a bin file
binayFilePath = 'D:\srcFile.Bin';
destinationBinaryFile = "D:\dstFile.Bin";
readFileId = fopen(binayFilePath, 'rb');
assert(readFileId > 0);
writeFileId = fopen(destinationBinaryFile, 'wb');
assert(writeFileId > 0);
%%
while ~feof(readFileId)
fileData = fread(readFileId, 1, 'bit64');
writeCount = fwrite(writeFileId, fileData, 'bit64');
end
fclose(readFileId);
fclose(writeFileId);
  2 Comments
Steven Lord
Steven Lord on 22 Jul 2020
J. Alex Lee, please post this as an Answer so we can vote for it and/or add comments related to this suggestion.

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Answers (2)

J. Alex Lee
J. Alex Lee on 23 Jul 2020
For your application does it make sense to just copy the file using a system command or matlab's coyfile?
  1 Comment
TripleSSSS
TripleSSSS on 23 Jul 2020
No.
I'd like to edit a binary file file the future - simply add few blocks here and there.
therefor - for making the opration right, it does make sence to binary copy with matlab...

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Walter Roberson
Walter Roberson on 23 Jul 2020
%%
% binary open a bin file
binayFilePath = 'D:\srcFile.Bin';
destinationBinaryFile = "D:\dstFile.Bin";
readFileId = fopen(binayFilePath, 'r'); %there is no 'b' flag
assert(readFileId > 0);
writeFileId = fopen(destinationBinaryFile, 'w');
assert(writeFileId > 0);
%%
buffersize = 1024;
while ~feof(readFileId)
fileData = fread(readFileId, buffersize, '*uint8');
writeCount = fwrite(writeFileId, fileData, 'uint8');
end
fclose(readFileId);
fclose(writeFileId);
The larger the buffer size that you use, the more efficient the I/O is.
You were using 'ubit64' as the precision. That is the same as 'ubit64=>double' which converted the uint64 to double, but uint64 to double loses values because double can only represent 53 bits.
As well, when you use ubit* then when you hit end of file if the count is not exhausted then it pads with bits of 0.

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