How to binary clone a file using fread and fwrite commands

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);

[J. Alex Lee]

Why not just use the system copy command or matlab copyfile function?

[Steven Lord]

J. Alex Lee, please post this as an Answer so we can vote for it and/or add comments related to this suggestion.

Answer 1

[J. Alex Lee]

For your application does it make sense to just copy the file using a system command or matlab's coyfile?

[TripleSSSS]

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...

Answer 2

[Walter Roberson]

%%
% 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.