Function to count the number of characters in a text file

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Sara Ismail-Sutton
Sara Ismail-Sutton 2020-9-16
评论： Sara Ismail-Sutton 2020-9-16
Hi
I've wrote the following code so far, but I'm having the problem that sum(charnums) returns the latest given value of charnums and doesn't sum over them. (as I can tell the code would, but I'm quite new to matlab and can't think how to write it with some index, for example i've tried charnums(oneline)=b2(oneline)... etc , as the 'oneline' is what is being iterated over I thought... but than it says dimensions exceed ... error .
many thanks
function[charnum]=liness(fname,character)
fid=fopen(fname,'rt')
if ( fid<0)
charnum=-1
return
else
a=findstr(oneline,character);
[b1,b2]=size(a);
charnums=b2
while ischar(oneline)
fprintf('%s',oneline)
a=findstr(oneline,character);
[b1,b2]=size(a);
charnums=b2
oneline=fgets(fid)
end
end
charnum=sum(b2)
fclose(fid)
end

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回答（1 个）

Walter Roberson
Walter Roberson 2020-9-16
a=findstr(oneline,character);
Your assignment requires you to determine that character is really a valid character and return -1 if it is not.
You have not defined oneline at that point.
[b1,b2]=size(a);
charnums=b2
hint: numel()
fprintf('%s',oneline)
You are not asked to display the content of oneline -- but it would not hurt to do so for debugging purposes, as long as you remove that afterwards.
charnums=b2
You are overwriting charnums each iteration of the while loop.
You also never use the value of charnums
charnum=sum(b2)
You overwrote all of b2 each iteration of the while loop.
Hint:
total = total + current_value
Also, your current logic has a problem in the case where the file exists and is readable but is completely empty, as the first read from such a file would immediately return an indication of end-of-file, and you should not be asking about the size of that end-of-file marker.
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Walter Roberson
Walter Roberson 2020-9-16
counter = 0;
while whatever
do something
counter = counter + 1;
[b1, b2(counter)] = size(a);
end
and then afterwards you can sum the vector b2.
However, this is really unnecessary and inefficient. Consider
counter = 0;
while whatever
do something
[b1, b2] = size(a);
counter = counter + b2;
end

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