fread: how to read n bytes from bin files

Question

Alexander Voznesensky 2017-7-7

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/347767-fread-how-to-read-n-bytes-from-bin-files

编辑： Guillaume 2017-7-10

Hi! I have a binary file. It consists of records: 8 byte long, 4 byte float, 4 byte float, 4 byte float. I want to read the file into array Nx4. N - records number. How can I do it? I tried fread but without result.

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Alexander Voznesensky 2017-7-7

在 MATLAB Online 中打开

Is it correct?

fid = fopen('acc-angle.bin', 'rb');  % открытие файла на чтение
if fid == -1                         % проверка корректности открытия
    error('File is not opened');
end
time=[];
ax=[];
ay=[];
az=[];
records_num=0;
while ~feof(fid)
      time = [time; fread(fid,1,'int64')];        
      ax= [ax; fread(fid,1,'float32')];        
      ay= [ay; fread(fid,1,'float32')];        
      az= [az; fread(fid,1,'float32')];    
      records_num=records_num+1;
end
fclose(fid);

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Answer 1

Guillaume 2017-7-7

2
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/347767-fread-how-to-read-n-bytes-from-bin-files#answer_273248

编辑：Guillaume 2017-7-8

在 MATLAB Online 中打开

Is it correct? The easiest way for you to find out is to try.

fid = fopen('acc-angle.bin', 'rb')

There's no 'b' option for fopen permissions. 'r' is all that is needed for binary.

Otherwise, your code looks ok to me as long as your file has little endian encoding. A faster option would be to read all records at once using the skip parameter of fread, something like:

fid = fopen('acc-angle.bin', 'r');
time = fread(fid, Inf, 'int64', 12);
fseek(fid, 'bof', 8);
ax = fread(fid, Inf, 'single', 16);
fseek(fid, 'bof', 12);
ay = fread(fid, Inf, 'single', 16);
fseek(fid, 'bof', 16);
az = fread(fid, Inf, 'single', 16);
fclose(fid);