I need help in the code. what am I doing wrong?

Question

Manav Divekar 2021-11-23

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回答： Johan 2021-11-23

I am writing a function to display host name from the url. This function should return only hostname without the port number

eg

Input: https://en.wikipedia.org:443/wiki/Kitten?printable=yes&download=no#External_links

Output: en.wikipedia.org

or

Input: http://www.google.com

Output: www.google.com

My code so far

function [result] = url2hostname(url)
c1 = strfind(url,'//');
ind1 = strfind(url,'/');
if isempty(c1) && isempty(ind1) 
    result = url; 
    return;
end
if ~isempty(c1)
    if numel(ind1)>2
        result = url(1:ind1(3)-1); 
    else
        result = url; 
    end
else
	
	result = url(1:ind1(1)-1); 
end
return;
result = result; 

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Answer 1

Johan 2021-11-23

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Hi,

I think you can just add a check for a ':' character in your code. Alternatively you can also use regular expression to do this kind of string manipulation. I put two exemples below:

1) The expression string tells regexp to match

any number of alphanumerical character: \w+

but only after it finds a :// character: (?<=://)

and only until it finds either a : or a / ?([^:]|/)+

expression = '(?<=://)\w+.?([^:]|/)+';
url = 'https://en.wikipedia.org:443/wiki/Kitten?printable=yes&download=no#External_links';
regexp(url,expression,'match')
ans = 1×1 cell array
    {'en.wikipedia.org'}
url = 'http://www.google.com';
regexp(url,expression,'match')
ans = 1×1 cell array
    {'www.google.com'}

2) Remake your code with simpler form of regexp to isolate the hostname of the url

url2hostname('http://www.google.com')
ans = 'www.google.com'
url2hostname('https://en.wikipedia.org:443/wiki/Kitten?printable=yes&download=no#External_links')
ans = 'en.wikipedia.org'
function result = url2hostname(url)
    tag = regexp(url,'//+');
    if ~isempty(tag)
        url = url(tag+2:end);
    end
    tag = regexp(url,'/','once');
    if ~isempty(tag)
        url = url(1:regexp(url,'./','once'));
    end
    tag = regexp(url,'.:','once');
    if ~isempty(tag)
        url = url(1:tag);
    end
    result = url;
end

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Answer 2

Ive J 2021-11-23

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This may help:

fnc = @(url) regexp(url, "(?<=https?://)(.*?)[^:]*", 'match');
fnc('https://en.wikipedia.org:443/wiki/Kitten?printable=yes&download=no#External_links')
ans = 1×1 cell array
    {'en.wikipedia.org'}
fnc('http://www.google.com')
ans = 1×1 cell array
    {'www.google.com'}