fprintf in nested for loops

Question

b 2017-6-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/344142-fprintf-in-nested-for-loops

评论： dpb 2017-6-10

Trying to fopen and fprintf the multiple files in nested for loops. Able to get the file opening to work:

for i=1:3 
  for j=1:4
    fname=['filei' num2str(i) 'j' num2str(j) '.txt'];
    fidsum=j+(i-1)*4;
    sprintf('fid%d',fidsum)=fopen(fname,'w');
  end 
end

But the fprintf part doesn't work. The following fails:

for k=1:largeNumber
  for i=1:3
    for j=1:4
      fidsum=j+(i-1)*4;
      if ((var1(k)==i) & (var2(k)==j))
        fprintf(sprintf('fid%d',fidsum),'%d\n',kDependentParameter)
      end
    end
  end
end

This also fails:

for k=1:largeNumber
  for i=1:3
    for j=1:4
      fidsum=j+(i-1)*4;
      if ((var1(k)==i) & (var2(k)==j))
        fid=sprintf('fid%d',fidsum);
        fprintf(fid,'%d\n',kDependentParameter)
      end
    end
  end
end

How to use the numerically increasing fid's for multiple file writings?

3 个评论
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b 2017-6-10

Thanks. Did not realize that indexing can be used for file identifiers also.

dpb 2017-6-10

在 MATLAB Online 中打开

>> help fopen
fopen  Open file.
  FID = fopen(FILENAME) opens the file FILENAME for read access.
  ... 
  FID is a scalar MATLAB integer valued double, called a file identifier. 
 ...

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Answer 1

dpb 2017-6-10

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/344142-fprintf-in-nested-for-loops#answer_270240

在 MATLAB Online 中打开

"Able to get the file opening to work"

Well, no, not really. What you've done is alias sprintf to a variable by assigning it in what looks to be array indexing syntax--

>> i=1;j=1;  % assign initial values
   fname=['filei' num2str(i) 'j' num2str(j) '.txt'];  % ok
   fidsum=j+(i-1)*4;                                  % fidsum --> 1 ok, but not sure what intend
   sprintf('fid%d',fidsum)=fopen(fname,'w');     % it all goes south here...
>>
>> whos sprintf
Name           Size            Bytes  Class     Attributes
sprintf      105x1               840  double              
>> which sprintf
sprintf is a variable.
>>

Do you really need all these files open at one time would be first question...but if do, keep the handles in an array...

I=3; J=4;           % loop limits
fid=zeros(I,J);     % preallocate to hold way too many fids at once in all likelihood
for i=1:I
  for j=1:J
    fname=sprintf('filei%02dj%02d.txt',i,j);  % build a file name
    fid(i,j)=fopen(fname,'w');                % and open a file, return fid in array  
  end
end