Editing a .c file using a .m file

I am trying to edit already existing c file using a .m file. I want to insert some characters in .c file. But my code is overwriting the .c file instead of inserting the characters. Following is my code

fileID = fopen('XYZ.c', 'r+'); a = fprintf(fileID,'\n%s\n','XYZ'); fclose(fileID);

Original .c file (just an example) : ABCDEF; ABCDEF; ABCDEF;

After editing the .c file it becomes as follows

XYZ F; ABCDEF; ABCDEF;

My expection was it should not overwrite anything in original c file :

XYZ

ABCDEF; ABCDEF; ABCDEF;

Please guide me how I should get my expected results

Answer 1

[Michael Haderlein]

Well, the pointer is at the beginning of the file and that's where the data is written. So the functions behave as they should.

If you wanted to attach some data at the end of the file, you could use the permission 'a+'. In case you want to extend the file at the beginning, I think you need to create an entire new file:

 readID=fopen('XYZ.c','r');
 writeID=fopen('NEW.c','w');
 fprintf(writeID,'%s\n','XYZ');
 fwrite(writeID,fread(readID));
 fclose(readID);
 fclose(writeID);

In principle, you can of course first read the file and then overwrite it (so both files are the same):

 fileID=fopen('test.txt','r+');
 data=fread(fileID);
 frewind(fileID);
 fprintf(fileID,'%s\n','XYZ');
 fwrite(fileID,data);
 fclose(fileID);
 edit test.txt

[Shrirang]

Yes, Creating a entirely new file is a good idea. Thank you !!!