Changing the header in a file which include binary content

Question

Beril Sirmacek 2018-4-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/394260-changing-the-header-in-a-file-which-include-binary-content

评论： Guillaume 2018-4-13

My ply file contains an ascii header and the rest of the mesh data content is written as binary. I would like to change lines 10, 11, 12 in the header with my specific content. I do not want to touch to the binary data which contains the mesh data. When I use the script below, my mesh data becomes like a flat surface instead of a 3D surface curvature. Why am I changing the rest of the content? How can I change the three header lines, without damaging the rest of the file?

A = regexp( fileread(ply), '\n', 'split');
A{10} = sprintf('%s',"header line 1");
A{11} = sprintf('%s',"header line 2");
A{12} = sprintf('%s',"header line 3");
fid = fopen(ply, 'wb');
fprintf(fid, A{:});
fclose(fid);

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Guillaume 2018-4-11

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/394260-changing-the-header-in-a-file-which-include-binary-content#answer_314622

在 MATLAB Online 中打开

For a start, you never put back all the \n characters that you've removed.

fprintf(fid, strjoin(A, '\n'));

may work. However, you're playing with fire here as you're interpreting binary data as text. There's no guarantee that the binary data will survive the round trip unaltered (e.g. the binary data forms an invalid character that could be ignored by regex).

And of course, it's possible that he binary data includes offset indicating where to find other binary data into the file, if you change the length of the header the offsets will point to the wrong location.

It's very unusual to have a file that's text and binary. It may be that some of the binary content is some textual data, but it should still be interpreted as binary. Usually text in a binary file is either fixed length, prefixed by binary data indicating how long the text is, or \0 terminated.

6 个评论
显示 4更早的评论隐藏 4更早的评论

Beril Sirmacek 2018-4-12

在 MATLAB Online 中打开

I cannot thank you enough! This does the work! Except a tiny typo at the second line :)

text = [];

Very great thanks!

Guillaume 2018-4-13

在 MATLAB Online 中打开

Well, it was meant to be:

text = {};

but either work.

请先登录，再进行评论。

Answer 2

Walter Roberson 2018-4-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/394260-changing-the-header-in-a-file-which-include-binary-content#answer_314623

在 MATLAB Online 中打开

When you split, the newlines are removed, and you are not putting them back.

fprintf(fid, '%s\n', A{1:end-1});
fprintf(fid, '%s', A{end});   %do not add extra \n at the end

but splitting the binary content is kinda dicey.

I would recommend that you instead switch to reading a limited number of lines using fgetl(), and write out the revised versions as required, and then fread() to end of file and fwrite() it to the new file.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Beril Sirmacek 2018-4-11

Thank you very much for your quick response. I have immediately tried out but I still have the same result. The mesh values are changed. The 3D structure becomes flat.

请先登录，再进行评论。