Text file I/O

Write a function called char_counter that counts the number of a certain character in a text file. The function takes two input arguments, fname, a char vector of the filename and character, the char it counts in the file. The function returns charnum, the number of characters found. If the file is not found or character is not a valid char, the function return -1. As an example, consider the following run. The file "simple.txt" contains a single line: "This file should have exactly three a-s..."

function charnum = char_counter(fname,character)
fid = fopen(fname,'rt') %gets the file
z=0;
charnum=0;
if fid < 0 || ~ischar(character) %checks if its valid, but I don't know how to return an "-1" if file missing
    charnum=-1    
end
  escrito = fgets(fid) 
for i=1:length(escrito) 
     z=z+1;
 if escrito(z)==char(character) %Here I check every position of the text to see if it's equal to the character
      charnum=charnum+1; %It sums everytime it happens
 end
end
 charnum %returns the sum
fprintf('\n');
fclose(fid);
end

The code works in the basic files, but fails at:

"Test with all visible characters

Variable charnum has an incorrect value. When testing with ' ' your solution returned 1 which is incorrect. (75444)"

And the "Non existent file" thing

Answer 1

[Voss]

Try this (and see the comments for explanation):

function charnum = char_counter(fname,character)

fid = fopen(fname); % opens the file for reading

% check that the file is valid, that 'character' is in fact a 
% character array (ischar), and that it is a single character (isscalar)
if fid < 0 || ~ischar(character) || ~isscalar(character)
    charnum=-1;
    return % return here, i.e., you cannot do the search in this case
end

% read the entire file, store the contents as a character row vector
% (there are plenty of other functions you can use to read a text file
% instead of fread)
escrito = fread(fid,'*char').';
fclose(fid);

% escrito == character is an array of logicals (true/false), one element
% per character in the file, with value 'true' where that character is the
% character you want to count.
% nnz is number of non-zero elements; when used with a logical array, it
% returns the number of elements that are 'true', so that's the count.
charnum = nnz(escrito == character);

% % this following way works too, except you don't need to use char() to convert
% % 'character' to a character; it already is a character - this was checked 
% % above using ischar()
% z = 0;
% charnum = 0;
% for i=1:length(escrito) 
%     z=z+1;
%     if escrito(z)==char(character) %Here I check every position of the text to see if it's equal to the character
%         charnum=charnum+1; %It sums everytime it happens
%     end
% end

end

[Raffael Leobino]

Oh, now I understood what was lacking in my code, thank you very much

[Voss]

You're welcome!