Writing a integer in an existing file

Hello,

I'm trying to overwrite a file with a int16 precission value and I'm not able to do it. I'm usign this code ('x.DBL' is the name of the file):

fp=fopen('x.DBL','r+');

fwrite(fp,dd,'int16'); %dd is a variable with 73 elements

The ans to that command is 0, so I'm realizing that it is not overwriting anything.

Before that, I've read dd by using dd=fread(fp,73,'int16'); and it works perfectly.

Can someone help me please? Thanks in advanced,

RRR

[Ameer Hamza]

This command is working fine on my system. Have you checked the content of the file using hexdump?

[Roselena Rubino]

fwrite(fp,dd,'int16'); is not able to write. I know it because its output is 0 showing that it didn't write any number in the file. :(

[Ameer Hamza]

Can you paste your code here exactly.

[Roselena Rubino]

fp=fopen(dbldir,'r+');
nmaps=fread(fp,1,'uint32'); %number of maps=13
for ii=1:nmaps
    fseek(fp,14,'cof');
    nlat=fread(fp,1,'uint16'); %number of latitudes=71
    for jj=1:nlat
        fseek(fp,20,'cof');
        nlon=fread(fp,1,'int16'); %number of longitudes=73
        Vm=iono_m(jj,1:nlon,ii);
        fwrite(fp,Vm(:),'int16'); %overwriting
%         fread(fp,nlon,'int16') %This is how the data is read and it works perfectly. I get 73 values
% % I try also this but it doesn't work
%         for oo=1:nlon
%             fwrite(fp,iono_m(jj,oo,ii),'int16'); %overwriting the VTEC
%         end
    end
fclose(fp);

My problem is when using fwrite

Answer 1

[Walter Roberson]

You must fseek every time you switch between reading and writing. Telling fseek to move 0 bytes cof is fine for this purpose.

[Roselena Rubino]

Thank you VERY MUCH. Problem solved. That was the issue.