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..."

charnum = char_counter('simple.txt','a')
charnum = 
   3

solution: this is copied from this link https://www.mathworks.com/matlabcentral/answers/453328-assignment-text-files-write-a-function-called-char_counter-that-counts-the-number-of-a-certain-char

function charnum = char_counter(fname,character)
fid=fopen(fname);
if fid< 0
    charnum = -1;
    return;
end
if strcmp(character,'')==1
    charnum=0;
    return;
end
if double(character)>=35 && double(character)<=43 && double(character) ~=39 && double(character) ~= 41 && double(character) ~= 40 
    charnum = 0;
    return;
end
if double(character) >=60 && double(character) <=64 && double(character) ~= 63 
    charnum = 0;
    return;
end
if double(character) == 81 || double(character) == 88 || double(character) == 90
    charnum = 0;
    return;
end
cc = fgets(fid);
sumv=0;
while ischar(cc)
    z = sprintf('%s',cc);
    k = strfind(z,character);
    sumv = sumv + length(k);
    cc = fgets(fid);
end
charnum = sumv;
if charnum == 0
    charnum =-1;
    return;
end

can you guys tell whats wrong with this code?

[Geoff Hayes]

asad - I'm not sure what your question is. If I run the code on a file that contains the line "This file should have exactly three a-s...", then the answer (from the function) is three...which is correct. What response or error are you observing?

[asad jaffar]

@Geoff hayes i am facing a problem for this example

Test with all visible characters

Variable charnum has an incorrect value. When testing with '' your solution returned -1 which is incorrect. (0).

can you tell me what can i do ?

[Ramesh Patel]

function charnum = char_counter(fname,character)
fid = fopen(fname,'rt');
if fid<0|| ~ischar(character)
    charnum=-1;
else
    charnum=0;
    oneline = fgets(fid);
    while ischar(oneline)
        n = strfind(oneline,character);
        charnum = charnum + length(n);
        oneline = fgets(fid);
    end
end
end

%this is simplest code and having no error

[Walter Roberson]

@Ramesh Patel

Your code does fopen() but no fclose(), and so does have an error.

Answer 1

[Jiaqi Liu]

function charnum = char_counter(frame,character)
fid = fopen(frame,'r');
if fid < 0
    charnum = -1;
    return
end
if ischar(character) == 0
    charnum = -1;
    return
end
inhalt = fscanf (fid, '%c');
charnum = count(inhalt,character);
end

[Aniket Bordekar]

Why is %c used?

[Walter Roberson]

fscanf() without a count asks MATLAB to read as far as possible in the file that still matches the given format. The format given is %c, which matches any one character, and since every byte stored in the file can be interpreted as a character, the result of using fscanf with '%c' format and no count, is to read the entire rest of the file one character at a time.

... Some day I should test with R2020a or later, and a byte stream that does not represent valid UTF8, to see whether %c would stop reading at that point...

Answer 2

[Muhammad Sadiq]

function charnum = char_counter(frame,character)
fid = fopen(frame,'r');
if fid < 0
    charnum = -1;
    return
end
if ischar(character) == 0
    charnum = -1;
    return
end
inhalt = fscanf (fid, '%c');
charnum = count(inhalt,character);
end

[Ankit Meena]

its working

[THIERNO AMADOU MOUCTAR BALDE]

perfect Thank sir

[Walter Roberson]

This code fails to fclose(fid) under any circumstances.

Answer 3

[Fazlul Haque]

done with fgets and while loops

[Walter Roberson]

If the file is valid but charv is not a character, then you leave the file open when you return.

We recommend against using sum as the name of a variable: it is very common to get confused and also want to use sum() as the name of the summation function in the same code where you use sum as a variable.

Answer 4

[Akshay Dengwani]

function charnum = char_counter(fname,charac)
fid = fopen(fname, 'rt');
if fid < 0 
    charnum = -1;
    return
end
line = fgets(fid);
su = 0;
while ischar(line)
    lo = line == charac;
    su = su + sum(lo(:));
    line = fgets(fid);
end
if double(charac)>127 || double(charac)<0 || ~ischar(charac);
    charnum = -1;
else
    charnum = su;
end
end
   

[Jan]

This code does not close the file properly. Then after a certain number of calls, Matlab cannot open any files anymore.

You could replace the while loop by reading the complete file at once:

line = fread(fid, inf, '*char');
su   = sum(line == charac);
fclose(fid);

[Akshay Dengwani]

Perfect Thank you

[SOUMYAJIT MONDAL]

Please explain

In the line sum(line==charac) , what does line==charac means ?

[Walter Roberson]

fread() with '*char' and inf size will cause fread() to return a character vector that contains all remaining characters in the file. Those will be stored in the variable named line

Character vectors are (for most purposes) stored as arrays of 16 bit integers that are unicode code points. Unicode is an international standard that gives a specific ordering to lots and lots of characters and symbols; https://home.unicode.org/ . For example the character 'A' is stored as 16 bit integer with value 65. They really are numeric internally (together with a flag that says that the numeric values represent characters.)

The == operator is the equality test operator. In this context, == is used to compare the character codes (integer) used to represent the data in the line variable, to the character code that is used to represent the character that is stored in charac which is known to be a single character. So internally you have a numeric vector ('line') being compared to a numeric scalar ('charac') . The result of comparing a vector and a scalar is defined by MATLAB to be a logical vector, in which the value is false for each place the comparison failed, an true for each place the comparison succeeded. So the output of == is a logical vector the same length as the variable line .

What you need to know after that point is that logical false is represented by numeric value 0, and logical true is represented by the numeric value 1. Because of that, when you want to know how many locations the comparison held at, you can sum() the vector, which contributes 1 to the sum for every true and the result at the end is going to be the number of places the comparison was true.

So what will be stored in su is the number of places a character in the variable line was the same as the character in the variable charac .

Answer 5

[Pranav Mishra]

function charnum = char_counter(fname,character)
fid = fopen(fname,'rt');
if (fid < 0)
    charnum = -1;
return;
end
if (ischar(character) ==0)
    charnum = -1;
else
    c = 0;
    oneline = fgets(fid);
    while ischar(oneline)
        character_line = char(oneline);
        [a b] = size(strfind(character_line,character));
        c = c + b;
        oneline = fgets(fid);
    end
        
  charnum = c;
end
fclose(fid);
end

[Walter Roberson]

Note that the result of fgets() is already a character vector (unless end of file), so you do not need to use char() on oneline.

Answer 6

[Hari Kiran Tirumaladasu]

function charnum = char_counter(fname,character)
fid = fopen(fname,'r');
if fid < 0 || ischar(character) == 0
    charnum = -1;
    error('The file entered is either incorrect or the character entered could not be found');
    return;
end
incount = fscanf(fid,'%c');
charnum = count(incount,character);

Answer 7

[Adityesh Satam]

I was able to get all correct using this code:

function charnum = char_counter(fname,character)
    fid = fopen(fname,'rt');
    charnum = 0;
    ii = 0;
    if fid < 0
        charnum = -1;
        return;
    end
    if ischar(character) == 0
        charnum = -1;
    end
    
    % Reading a file one line at a time
    one_line = fgets(fid);
    while ischar(one_line)
        for ii = 1:length(one_line)
            if strcmp(one_line(ii),character) && ischar(character)
                charnum = charnum + 1;
            end
        end
        one_line = fgets(fid);
    end
    fclose(fid);
end

[Walter Roberson]

If the character parameter is not a valid parameter, you go ahead and read the file anyhow, but each time testing again that ischar(character) is true. That is a waste of time. If ischar(character) is false then do not bother reading the file.

Answer 8

[Walter Roberson]

We already explained. If you are passed something that is a character but the character is not found in the file then you need to return 0 not -1. Only return -1 if the file does not exist or what you are passed is not character data type.

[asad jaffar]

@walter roberson can you tell me the line number where i have to return 0 and not -1 , i mean to say at which line do i have to make changes?

[Walter Roberson]

Line 33.

Answer 9

[Arup Kumar Debnath]

I was trying to answer this question. But i stuck there, Can any one help me and find the fault in this code?

Disclaimer= I am a noob here.

function charnum=char_counter(fname,character)
fid=fopen(fname,'rt');
if fid<0
    error('error opening file\n');
    charnum=-1;
    return;
end
total=fgets(fid);
ii=1;
a=size(total);
charnum=0;
while ii<=a
if total(ii)=='character';
charnum=charnum+1;
else 
ii=ii+1;
end
end

[Walter Roberson]

you do not validate that the second input is a character.

You are comparing the input to the literal character vector ['c' 'h' 'a' 'r' 'a' 'c' 't' 'e' 'r'] instead of to what the input variable named character holds.

You are not incrementing ii if the comparison is true.

Answer 10

[SHASHANK SINGH]

function charnum = char_counter(fname, character)
fid = fopen(fname,'r');
if fid < 0 || ischar(character) == 0
    charnum = -1;
    return
end
  inhalt = fscanf(fid, '%c');
charnum = count(inhalt, character);
end

[Walter Roberson]

If the fname is valid but character is not a character, then you leave the file open when you return.

[Jobin Geevarghese Thampi]

@Walter Roberson what happens when we doesnt write 'return'. i havent understood about return function could you explain me?

[Walter Roberson]

When return is encountered, MATLAB leaves the function and goes back to the place it was called, exactly the same as if MATLAB had reached the end of the function. It does not execute any more code in the function.

In the code that Shashank Singh posted, if the return had not been there, then after charnum was assigned -1, the code would continue on after the if , and so the code would attempt to do the fscanf(). But if the fid was < 0 indicating the file could not be opened, then fscanf(fid) would be an error and the function would crash.

It is always possible to rewrite code that uses return to not use return, but it can be messy to do so. In the case of the above code it could be instead written as

function charnum = char_counter(fname, character)
    fid = fopen(fname,'r');
    if fid < 0 || ischar(character) == 0
        charnum = -1;
    else
      inhalt = fscanf(fid, '%c');
      charnum = count(inhalt, character);
    end
end

which is not bad at all in this case. But consider proper checking of ischar():

function charnum = char_counter(fname, character)
    if ischar(character) == 0
        charnum = -1;
    else
      fid = fopen(fname,'r');
      if fid < 0
        charnum = -1;
      else
        inhalt = fscanf(fid, '%c');
        charnum = count(inhalt, character);
      end
    end
end

and compare that to the same with return:

function charnum = char_counter(fname, character)
    if ischar(character) == 0
        charnum = -1;
        return
    end
    fid = fopen(fname,'r');
    if fid < 0
        charnum = -1;
        return
    end
    inhalt = fscanf(fid, '%c');
    charnum = count(inhalt, character);
end

Notice that using return the code is more compact and does not need as many if/else levels.

Answer 11

[Ujjawal Barnwal]

function charnum = char_counter(fname,character)
fid = fopen(fname,'rt');
charnum = 0;
if fid < 0 || ~ischar(character)
    charnum = -1;
    return;
end
oneline = fgets(fid);
while ischar(oneline)
    a=length(findstr(oneline,character));
    charnum = charnum + a;
    oneline = fgets(fid);
end
fclose(fid);
end

[Walter Roberson]

If the fname is valid but character is not a character, then you leave the file open when you return.

Answer 12

[Sachin Patare]

function charnum=char_counter(fname,character)
fid=fopen(fname,'rt');
if fid<0
    charnum=-1;
    return
end
x=fileread(fname);
if ischar(character)==1
    a=findstr(x,character);
    b=size(a);
    charnum=b(1,2);
else
    charnum=-1;
end

[Walter Roberson]

How many files are open after the code returns?

[Jan]

If you use fileread, you can omit the fopen. If you use fopen, do not forget to close the file with fclose.

numel() is easier than getting the 2nd output from size. ischar replies a logical already, so there is no need to compare it with "== 1".

findstr is deprecated for more than 10 years now. Use strfind instead.

function charnum=char_counter(fname, character)
charnum = -1;                 % Default value
if exist(fname, 'file') == 2  % Check existence of file
  s = fileread(fname);
  if ischar(character) && isscalar(character)
    charnum = sum(s == character);
    % Or charnum = numel(strfind(s, character));
  end
end

[Walter Roberson]

The one advantage of testing the fopen() over testing file existence with exist, is that fopen() will fail smoothly if the file exists but you do not have permission to read it, or the file exists but it is locked so you cannot read it at the moment. In either of those cases, fileread() would generate an exception that would have to be handled with a try/catch to replicate the fopen() ability to detect that the file cannot be read.

Answer 13

[Sumanth Bayya]

function charnum=char_counter(fname,character)
fid=fopen(fname,'rt');
charnum=0;
ii=0;
if fid<0 
      charnum=-1;
      return
end
if ischar(character)==0
    charnum=-1;
end
one_line=fgets(fid);
while ischar(one_line)
    for ii=1:length(one_line)
        if strcmp(one_line(ii),character)&& ischar(character)
            charnum=charnum+1;
        end
    end
    one_line=fgets(fid);
end
fclose(fid);
end

[Rik]

Same question as with your other answer: what does this add?

Also, you forgot a return statement (and fclose) after the ischar test. Otherwise the situation below will make your code error.

character={1,2};
ii=1;one_line(ii)='1';
strcmp(one_line(ii),character)&& ischar(character)

Operands to the logical and (&&) and or (||) operators must be convertible to logical scalar values.

[Jan]

@Rik: Do you know, in which format the code of this answer is posted? There is no box around the code, so it is not the code environment. But the syntax highlighting and font looks like code. In my browser it is a 1 or 2 point smaller font. When I edit it, a blue box appears around the code. It is not a screenshot and hitting the Run button explains, that there is no code.

@Sumanth Bayya: How did you insert the code?

[Walter Roberson]

@Jan

If you look at the right hand side of the "Insert" controls, the blob to the right of the paperclip is the "Code examples" button. It allows you to insert formatted code that is not executed if you "Run".

This is one of the facilities carried over from LiveScript. In the context of LiveScript it makes more sense that there would be cases where you need a block of code to be formatted but not executable.

[Jan]

% I got it. Thanks, Walter

Answer 14

[Milad Mehrnia]

function charnum = char_counter(fname,c)
fid = fopen(fname,'rt');
charnum = 0;
if ~ischar(c)
    charnum = -1;
elseif fid < 0
    charnum = -1;
else
    line = fgets(fid);
    while ischar(line)
        for i = 1:length(line)
            if line(1,i) == c
                charnum = charnum + 1;
            end
        end
        line = fgets(fid);
    end
    fclose(fid);
end
end

[Walter Roberson]

In the case where the file exists and is readable, but the user entered something that was not a character for the second parameter, then you open the file but you do not close it.

Answer 15

[Duong Nguyen]

function charnum = char_counter(fname,character)
fid = fopen(fname, 'rt');
charnum = 0;
if fid<0||~(ischar(character))
    charnum = -1;
    return
end
%if you not use 'return' the while loop below will assign charnum = 0;
oneline = fgets(fid);
while ischar(oneline)
    [~,temp] = size(strfind(oneline,character));
    charnum = charnum + temp;
    oneline = fgets(fid);
end
fclose(fid);

[Walter Roberson]

In the case where the file exists and is readable, but the user entered something that was not a character for the second parameter, then you open the file but you do not close it.

Answer 16

[Zia Ur Rehman]

Hi folks,

please check my code and suggest me if I can improve this

function charnum = char_counter(fname,character)
fid = fopen(fname,'rt'); % opening the text named(fname) file to read(rt)
if fid<0 || ~ischar(character) % checking the existance of file and checking if second argument of char_counter is valid char 
    %fprintf('Error opening file %s\n\n',fname);
    charnum = -1;
    return;
end
charnum=0;
oneline = fgets(fid); % reading 1st line using 'fgets' 
while ischar(oneline)
    for i = 1:length(oneline) % loop for traversing through each char of the line
        b = strcmp(oneline(i),character); % comparing ith char with 2nd argument(character)
        if b
            charnum= charnum+1; % if we find the char then add 1
        end
    end
    oneline = fgets(fid); %reading the next line and returned to online 
end
fclose(fid); % closing the file
end

[Rik]

If character is invalid or any error occurs in your function you will end up with an unclosed file. And why not use fileread? Then you can process the entire file without a loop.

[Zia Ur Rehman]

ok ok, thanks

[Zia Ur Rehman]

please check my code now, thanks

function charnum = char_counter1(fname,character)
fid = fopen(fname,'rt'); % opening the text named(fname) file to read(rt)
if fid<0  % checking the existance of file 
    %fprintf('Error opening file %s\n\n',fname);
    charnum = -1;
    return;
end
if ~ischar(character) % checking if second argument of char_counter is valid char
        charnum = -1;
    fclose(fid); % closing the file
    return;
end
% not using this (if fid<0 || ~ischar(character)) as a single condition because when file is valid and character is not a char so our file will remail unclosed
charnum=0;
file_text = fileread(fname);
    for i = 1:length(file_text) % loop for traversing through each char of the line
        b = strcmp(file_text(i),character); % comparing ith char with 2nd argument(character)
        if b
            charnum= charnum+1; % if we find the char then add 1
        end
    end
fclose(fid); % closing the file
end

[Rik]

Why not just use fileread, sum, and ismember (or even ==)? You don't need any loops. If you want to confirm a file exists you can use the exist function. You really only need a handful of lines of code for this function.

[Jan]

@Zia Ur Rehman: If you use fileread, there is no need to open the file with fopen before.

You can simplify:

b = strcmp(file_text(i),character); % comparing ith char with 2nd argument(character)
if b
    charnum= charnum+1; % if we find the char then add 1
end

to

charnum = charnum + strcmp(file_text(i),character);

strcmp replies true or false, which is converted to 1 or 0.

But you can avoid the loop: file_text == character replies a vector of 0 and 1 also. Then sum() counts the matchs.

See also: isfile, fileread. Then 6 lines of code solve the problem.

[Zia Ur Rehman]

ok ok, i will try this, thanks a lot

Answer 17

[Rahim Ullah]

your code looks lengthy and complex please try this one

function charnum=char_counter(fname,character)
fid=fopen(fname,'rt');  %file open
if fid<0    %check if the file open correctly or not
   fprintf('file cant be open')
    charnum=-1; %in case file is not opened due to any reason
    return
end
file_content=fileread(fname); % reads the file contents and store it as a string

charnum=sum(file_content==character); %sum all the matching characters found in the strings
if ischar(character)==0 %check for valid character
    charnum=-1;
    return
end

[Walter Roberson]

you do not fclose()

[Rahim Ullah]

Yes since we have only read the file and haven’t add anything into the txt file so there is no need to add fclose() since it will nit cause any error

[Jan]

@Rahim Ullah: It does not cause an error immediatly. But the number of files, which can be open at the same time, is limited by the OS. 255 is a typical limit. So after calling your function 255 time, you cannot open any other file anymore.

You find shorter and more elegant version in this thread already. The question is almost 4 years old. So why do you post this answer?

function charnum = char_counter(fname, character)
charnum = -1;
if isfile(fname) && isscalar(character) && ischar(character)
   charnum = sum(fileread(fname) == character);
end
end

[Rahim Ullah]

So should I delete my answer now ???

[Jan]

@Rahim Ullah: Your answer is a valid contribution concerning Matlab and does not violate the policies. Therefore the editors will not remove it.

I'd insert an fclose(fid) or use isfile() instead. But this is your contribution. Feel free to do, what you like.