saving data to the file

How to use function fprintf in Matlab2016b? Why thoe following comands are uncorrect?

fid = fopen('file.txt','a');
fprintf(fid,'%.6f %.6f %.6f\n',xw,yw,rw);
fclose(fid);

[KSSV]

fid = fopen('file.txt','a'); 
xw = rand(1) ;
yw = rand(1) ;
rw = rand(1) ;
fprintf(fid,'%.6f %.6f %.6f\n',xw,yw,rw); 
fclose(fid);

works very fine....what error it pop's out for you?

[José-Luis]

What's the error message you are getting?

[Artur Lipnicki]

Error using fprintf Invalid file identifier. Use fopen to generate a valid file identifier.

[José-Luis]

What's the value of fid?

Do you have write access to the current folder?

Answer 1

[Pritesh Shah]

Did you defined the variable xw,yw,rw?

Answer 2

[Guillaume]

Matlab failed to open the file. There may be many reasons for this, the file does not exist / the file is not is in the current directory (since you didn't specify a path) / you don't have read access to the file / something else.

Open the file with

[fid, errmsg] = fopen('file.txt', 'a');
assert(fid > 0, 'Failed to open file because: %s', errmsg);

And see what error you get.