Converting A Host Name to a Domain Name in C++ : 5ubliminal's TellinYa

<a href="http://www.tellinya.com/art2/191/">Converting A Host Name to a Domain Name in C++ : 5ubliminal's TellinYa</a>
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There's nothing more fun for C/C++ coder than playing with strings. This is what we do best and this is a bit is string playing for you! There's also a new version for PHP to extract domain from url in PHP.
Extracting Domain Name From Host Name? Easy Task …

I would not really call this easy! Many would think this is simple to do. You just extract last 2 pieces of the hostname and, bang! You have a domain name for use. Well … what do you do about .co.uk or net.ec. These are the top level domains hence the domain name will be formed by the last 3 pieces of the hostname.

If you want to make it really difficult to parse the domain name from host name you start to play with Whois and DNS lookups which will waste any performance you application used to have. This code needs nothing else but it's own. Not even an internet connection :)

Unfortunately there is no work around!

If you try to consider the last two pieces as a TLD (as .co.uk) by their lengths you might be wrong. You actually need a predefined list to use with the ones that are oficially established to have a properly working code. So I did some research and found these on this site.

How the code works?

You will notice I commented it but I will explain you what it does in a few lines here.

  1. We validate the parameters. Null and 0 length are unacceptable.
  2. We check if the paramater is not an url ://host/ and if it is we extract the host name.
  3. We lowercase the hostname and count the DOTS.
  4. If we have 1 DOT it must be a domain name and we return it!
  5. If we have more then 2 dots we strip away first parts as a maximum of 2 DOTS (3 pieces can form a domain name).
  6. We check if the last 2 pieces of the hostname match any of the predefined second level domain names and if any does we return the entire 3 parts domain name.
  7. Otherwise we only return the last 2 pieces of the host name.
  8. Caution: Free the returned string after use with free()!

The C++ Source Code:

I needed this to play with some Whois queries and, as I did not find any code online to do it, here it is. Might come in handy to some C++ coders.

inline LPTSTR Url2Domain(LPCTSTR szUrl){
     //-----------------------------------------------
     // These 2 should never happen
     if(!szUrl || !_tcslen(szUrl)) return 0;
     LPTSTR szHost=_tcsdup(szUrl);
     // To free it!
     LPTSTR szPtrMark=szHost;
     //-----------------------------------------------
     { // We check if there was an URL as parameter
          LPTSTR UrlHostMark=_tcsstr(szHost,_T("://"));
          if(UrlHostMark){ // We get Host from URL
               UrlHostMark+=3;
               szHost=UrlHostMark;
               LPTSTR DummyMark=szHost;
               while(*DummyMark){
                    if(_tcschr(_T("/?#"),*DummyMark)) break;
                    DummyMark++;
               }
               if(*DummyMark) *DummyMark='\0';
          } // We got the host from URL
     }
     //-----------------------------------------------
     BYTE Dots = 0;
     { // We lowercase the hostname
          LPTSTR DummyMark=szHost;
          while(*DummyMark){
               if(*DummyMark=='.') Dots++;
               if(_istupper(*DummyMark))
                    *DummyMark=_tolower(*DummyMark);
               DummyMark++;
          }
     } // - We lowercase the hostname
     //-----------------------------------------------
     // If we have a host with only 1 dot it has to be
     // a valid domain name !
     if(Dots<2){
          LPTSTR Host=_tcsdup(szHost);
          free(szPtrMark);
          return Host;
     }
     // We can not have more then 2 dots in a domain name
     // so we just strip the extra fat !
     if(Dots>2){
          BYTE Extras=Dots-2;
          while(Extras>0){
               szHost=_tcschr(szHost,'.')+1;
               Extras--;
          }
     }
     //-----------------------------------------------
     TCHAR szSLTLDs[]=
          _T("com.ac,edu.ac,gov.ac,net.ac,mil.ac,org.ac,com.ae,n")
          _T("et.ae,org.ae,gov.ae,ac.ae,co.ae,sch.ae,pro.ae,com.")
          _T("ai,org.ai,edu.ai,gov.ai,com.ar,net.ar,org.ar,gov.a")
          _T("r,mil.ar,edu.ar,int.ar,co.at,ac.at,or.at,gv.at,pri")
          _T("v.at,com.au,gov.au,org.au,edu.au,id.au,oz.au,info.")
          _T("au,net.au,asn.au,csiro.au,telememo.au,conf.au,otc.")
          _T("au,id.au,com.az,net.az,org.az,com.bb,net.bb,org.bb")
          _T(",ac.be,belgie.be,dns.be,fgov.be,com.bh,gov.bh,net.")
          _T("bh,edu.bh,org.bh,com.bm,edu.bm,gov.bm,org.bm,net.b")
          _T("m,adm.br,adv.br,agr.br,am.br,arq.br,art.br,ato.br,")
          _T("bio.br,bmd.br,cim.br,cng.br,cnt.br,com.br,coop.br,")
          _T("ecn.br,edu.br,eng.br,esp.br,etc.br,eti.br,far.br,f")
          _T("m.br,fnd.br,fot.br,fst.br,g12.br,ggf.br,gov.br,imb")
          _T(".br,ind.br,inf.br,jor.br,lel.br,mat.br,med.br,mil.")
          _T("br,mus.br,net.br,nom.br,not.br,ntr.br,odo.br,org.b")
          _T("r,ppg.br,pro.br,psc.br,psi.br,qsl.br,rec.br,slg.br")
          _T(",srv.br,tmp.br,trd.br,tur.br,tv.br,vet.br,zlg.br,c")
          _T("om.bs,net.bs,org.bs,ab.ca,bc.ca,mb.ca,nb.ca,nf.ca,")
          _T("nl.ca,ns.ca,nt.ca,nu.ca,on.ca,pe.ca,qc.ca,sk.ca,yk")
          _T(".ca,gc.ca,co.ck,net.ck,org.ck,edu.ck,gov.ck,com.cn")
          _T(",edu.cn,gov.cn,net.cn,org.cn,ac.cn,ah.cn,bj.cn,cq.")
          _T("cn,gd.cn,gs.cn,gx.cn,gz.cn,hb.cn,he.cn,hi.cn,hk.cn")
          _T(",hl.cn,hn.cn,jl.cn,js.cn,ln.cn,mo.cn,nm.cn,nx.cn,q")
          _T("h.cn,sc.cn,sn.cn,sh.cn,sx.cn,tj.cn,tw.cn,xj.cn,xz.")
          _T("cn,yn.cn,zj.cn,arts.co,com.co,edu.co,firm.co,gov.c")
          _T("o,info.co,int.co,nom.co,mil.co,org.co,rec.co,store")
          _T(".co,web.co,ac.cr,co.cr,ed.cr,fi.cr,go.cr,or.cr,sa.")
          _T("cr,com.cu,net.cu,org.cu,ac.cy,com.cy,gov.cy,net.cy")
          _T(",org.cy,co.dk,art.do,com.do,edu.do,gov.do,gob.do,o")
          _T("rg.do,mil.do,net.do,sld.do,web.do,com.dz,org.dz,ne")
          _T("t.dz,gov.dz,edu.dz,ass.dz,pol.dz,art.dz,com.ec,k12")
          _T(".ec,edu.ec,fin.ec,med.ec,gov.ec,mil.ec,org.ec,net.")
          _T("ec,com.ee,pri.ee,fie.ee,org.ee,med.ee,com.eg,edu.e")
          _T("g,eun.eg,gov.eg,net.eg,org.eg,sci.eg,com.er,net.er")
          _T(",org.er,edu.er,mil.er,gov.er,ind.er,com.es,org.es,")
          _T("gob.es,edu.es,nom.es,com.et,gov.et,org.et,edu.et,n")
          _T("et.et,biz.et,name.et,info.et,ac.fj,com.fj,gov.fj,i")
          _T("d.fj,org.fj,school.fj,com.fk,ac.fk,gov.fk,net.fk,n")
          _T("om.fk,org.fk,asso.fr,nom.fr,barreau.fr,com.fr,prd.")
          _T("fr,presse.fr,tm.fr,aeroport.fr,assedic.fr,avocat.f")
          _T("r,avoues.fr,cci.fr,chambagri.fr,chirurgiens-dentis")
          _T("tes.fr,experts-comptables.fr,geometre-expert.fr,go")
          _T("uv.fr,greta.fr,huissier-justice.fr,medecin.fr,nota")
          _T("ires.fr,pharmacien.fr,port.fr,veterinaire.fr,com.g")
          _T("e,edu.ge,gov.ge,mil.ge,net.ge,org.ge,pvt.ge,co.gg,")
          _T("org.gg,sch.gg,ac.gg,gov.gg,ltd.gg,ind.gg,net.gg,al")
          _T("derney.gg,guernsey.gg,sark.gg,com.gr,edu.gr,gov.gr")
          _T(",net.gr,org.gr,com.gt,edu.gt,net.gt,gob.gt,org.gt,")
          _T("mil.gt,ind.gt,com.gu,edu.gu,net.gu,org.gu,gov.gu,m")
          _T("il.gu,com.hk,net.hk,org.hk,idv.hk,gov.hk,edu.hk,co")
          _T(".hu,2000.hu,erotika.hu,jogasz.hu,sex.hu,video.hu,i")
          _T("nfo.hu,agrar.hu,film.hu,konyvelo.hu,shop.hu,org.hu")
          _T(",bolt.hu,forum.hu,lakas.hu,suli.hu,priv.hu,casino.")
          _T("hu,games.hu,media.hu,szex.hu,sport.hu,city.hu,hote")
          _T("l.hu,news.hu,tozsde.hu,tm.hu,erotica.hu,ingatlan.h")
          _T("u,reklam.hu,utazas.hu,ac.id,co.id,go.id,mil.id,net")
          _T(".id,or.id,co.il,net.il,org.il,ac.il,gov.il,k12.il,")
          _T("muni.il,idf.il,co.im,net.im,org.im,ac.im,lkd.co.im")
          _T(",gov.im,nic.im,plc.co.im,co.in,net.in,ac.in,ernet.")
          _T("in,gov.in,nic.in,res.in,gen.in,firm.in,mil.in,org.")
          _T("in,ind.in,ac.ir,co.ir,gov.ir,id.ir,net.ir,org.ir,s")
          _T("ch.ir,ac.je,co.je,net.je,org.je,gov.je,ind.je,jers")
          _T("ey.je,ltd.je,sch.je,com.jo,org.jo,net.jo,gov.jo,ed")
          _T("u.jo,mil.jo,ad.jp,ac.jp,co.jp,go.jp,or.jp,ne.jp,gr")
          _T(".jp,ed.jp,lg.jp,net.jp,org.jp,gov.jp,hokkaido.jp,a")
          _T("omori.jp,iwate.jp,miyagi.jp,akita.jp,yamagata.jp,f")
          _T("ukushima.jp,ibaraki.jp,tochigi.jp,gunma.jp,saitama")
          _T(".jp,chiba.jp,tokyo.jp,kanagawa.jp,niigata.jp,toyam")
          _T("a.jp,ishikawa.jp,fukui.jp,yamanashi.jp,nagano.jp,g")
          _T("ifu.jp,shizuoka.jp,aichi.jp,mie.jp,shiga.jp,kyoto.")
          _T("jp,osaka.jp,hyogo.jp,nara.jp,wakayama.jp,tottori.j")
          _T("p,shimane.jp,okayama.jp,hiroshima.jp,yamaguchi.jp,")
          _T("tokushima.jp,kagawa.jp,ehime.jp,kochi.jp,fukuoka.j")
          _T("p,saga.jp,nagasaki.jp,kumamoto.jp,oita.jp,miyazaki")
          _T(".jp,kagoshima.jp,okinawa.jp,sapporo.jp,sendai.jp,y")
          _T("okohama.jp,kawasaki.jp,nagoya.jp,kobe.jp,kitakyush")
          _T("u.jp,utsunomiya.jp,kanazawa.jp,takamatsu.jp,matsuy")
          _T("ama.jp,com.kh,net.kh,org.kh,per.kh,edu.kh,gov.kh,m")
          _T("il.kh,ac.kr,co.kr,go.kr,ne.kr,or.kr,pe.kr,re.kr,se")
          _T("oul.kr,kyonggi.kr,com.kw,net.kw,org.kw,edu.kw,gov.")
          _T("kw,com.la,net.la,org.la,com.lb,org.lb,net.lb,edu.l")
          _T("b,gov.lb,mil.lb,com.lc,edu.lc,gov.lc,net.lc,org.lc")
          _T(",com.lv,net.lv,org.lv,edu.lv,gov.lv,mil.lv,id.lv,a")
          _T("sn.lv,conf.lv,com.ly,net.ly,org.ly,co.ma,net.ma,or")
          _T("g.ma,press.ma,ac.ma,com.mk,com.mm,net.mm,org.mm,ed")
          _T("u.mm,gov.mm,com.mn,org.mn,edu.mn,gov.mn,museum.mn,")
          _T("com.mo,net.mo,org.mo,edu.mo,gov.mo,com.mt,net.mt,o")
          _T("rg.mt,edu.mt,tm.mt,uu.mt,com.mx,net.mx,org.mx,gob.")
          _T("mx,edu.mx,com.my,org.my,gov.my,edu.my,net.my,com.n")
          _T("a,org.na,net.na,alt.na,edu.na,cul.na,unam.na,telec")
          _T("om.na,com.nc,net.nc,org.nc,ac.ng,edu.ng,sch.ng,com")
          _T(".ng,gov.ng,org.ng,net.ng,gob.ni,com.ni,net.ni,edu.")
          _T("ni,nom.ni,org.ni,com.np,net.np,org.np,gov.np,edu.n")
          _T("p,ac.nz,co.nz,cri.nz,gen.nz,geek.nz,govt.nz,iwi.nz")
          _T(",maori.nz,mil.nz,net.nz,org.nz,school.nz,com.om,co")
          _T(".om,edu.om,ac.om,gov.om,net.om,org.om,mod.om,museu")
          _T("m.om,biz.om,pro.om,med.om,com.pa,net.pa,org.pa,edu")
          _T(".pa,ac.pa,gob.pa,sld.pa,edu.pe,gob.pe,nom.pe,mil.p")
          _T("e,org.pe,com.pe,net.pe,com.pg,net.pg,ac.pg,com.ph,")
          _T("net.ph,org.ph,mil.ph,ngo.ph,aid.pl,agro.pl,atm.pl,")
          _T("auto.pl,biz.pl,com.pl,edu.pl,gmina.pl,gsm.pl,info.")
          _T("pl,mail.pl,miasta.pl,media.pl,mil.pl,net.pl,nieruc")
          _T("homosci.pl,nom.pl,org.pl,pc.pl,powiat.pl,priv.pl,r")
          _T("ealestate.pl,rel.pl,sex.pl,shop.pl,sklep.pl,sos.pl")
          _T(",szkola.pl,targi.pl,tm.pl,tourism.pl,travel.pl,tur")
          _T("ystyka.pl,com.pk,net.pk,edu.pk,org.pk,fam.pk,biz.p")
          _T("k,web.pk,gov.pk,gob.pk,gok.pk,gon.pk,gop.pk,gos.pk")
          _T(",edu.ps,gov.ps,plo.ps,sec.ps,com.pt,edu.pt,gov.pt,")
          _T("int.pt,net.pt,nome.pt,org.pt,publ.pt,com.py,net.py")
          _T(",org.py,edu.py,com.qa,net.qa,org.qa,edu.qa,gov.qa,")
          _T("asso.re,com.re,nom.re,com.ro,org.ro,tm.ro,nt.ro,no")
          _T("m.ro,info.ro,rec.ro,arts.ro,firm.ro,store.ro,www.r")
          _T("o,com.ru,net.ru,org.ru,gov.ru,pp.ru,com.sa,edu.sa,")
          _T("sch.sa,med.sa,gov.sa,net.sa,org.sa,pub.sa,com.sb,n")
          _T("et.sb,org.sb,edu.sb,gov.sb,com.sd,net.sd,org.sd,ed")
          _T("u.sd,sch.sd,med.sd,gov.sd,tm.se,press.se,parti.se,")
          _T("brand.se,fh.se,fhsk.se,fhv.se,komforb.se,kommunalf")
          _T("orbund.se,komvux.se,lanarb.se,lanbib.se,naturbruks")
          _T("gymn.se,sshn.se,org.se,pp.se,com.sg,net.sg,org.sg,")
          _T("edu.sg,gov.sg,per.sg,com.sh,net.sh,org.sh,edu.sh,g")
          _T("ov.sh,mil.sh,gov.st,saotome.st,principe.st,consula")
          _T("do.st,embaixada.st,org.st,edu.st,net.st,com.st,sto")
          _T("re.st,mil.st,co.st,com.sv,org.sv,edu.sv,gob.sv,red")
          _T(".sv,com.sy,net.sy,org.sy,gov.sy,ac.th,co.th,go.th,")
          _T("net.th,or.th,com.tn,net.tn,org.tn,edunet.tn,gov.tn")
          _T(",ens.tn,fin.tn,nat.tn,ind.tn,info.tn,intl.tn,rnrt.")
          _T("tn,rnu.tn,rns.tn,tourism.tn,com.tr,net.tr,org.tr,e")
          _T("du.tr,gov.tr,mil.tr,bbs.tr,k12.tr,gen.tr,co.tt,com")
          _T(".tt,org.tt,net.tt,biz.tt,info.tt,pro.tt,int.tt,coo")
          _T("p.tt,jobs.tt,mobi.tt,travel.tt,museum.tt,aero.tt,n")
          _T("ame.tt,gov.tt,edu.tt,nic.tt,us.tt,uk.tt,ca.tt,eu.t")
          _T("t,es.tt,fr.tt,it.tt,se.tt,dk.tt,be.tt,de.tt,at.tt,")
          _T("au.tt,co.tv,com.tw,net.tw,org.tw,edu.tw,idv.tw,gov")
          _T(".tw,com.ua,net.ua,org.ua,edu.ua,gov.ua,ac.ug,co.ug")
          _T(",or.ug,go.ug,co.uk,me.uk,org.uk,edu.uk,ltd.uk,plc.")
          _T("uk,net.uk,sch.uk,nic.uk,ac.uk,gov.uk,nhs.uk,police")
          _T(".uk,mod.uk,dni.us,fed.us,com.uy,edu.uy,net.uy,org.")
          _T("uy,gub.uy,mil.uy,com.ve,net.ve,org.ve,co.ve,edu.ve")
          _T(",gov.ve,mil.ve,arts.ve,bib.ve,firm.ve,info.ve,int.")
          _T("ve,nom.ve,rec.ve,store.ve,tec.ve,web.ve,co.vi,net.")
          _T("vi,org.vi,com.vn,biz.vn,edu.vn,gov.vn,net.vn,org.v")
          _T("n,int.vn,ac.vn,pro.vn,info.vn,health.vn,name.vn,co")
          _T("m.vu,edu.vu,net.vu,org.vu,de.vu,ch.vu,fr.vu,com.ws")
          _T(",net.ws,org.ws,gov.ws,edu.ws,ac.yu,co.yu,edu.yu,or")
          _T("g.yu,com.ye,net.ye,org.ye,gov.ye,edu.ye,mil.ye,ac.")
          _T("za,alt.za,bourse.za,city.za,co.za,edu.za,gov.za,la")
          _T("w.za,mil.za,net.za,ngo.za,nom.za,org.za,school.za,")
          _T("tm.za,web.za,co.zw,ac.zw,org.zw,gov.zw,eu.org,au.c")
          _T("om,br.com,cn.com,de.com,de.net,eu.com,gb.com,gb.ne")
          _T("t,hu.com,no.com,qc.com,ru.com,sa.com,se.com,uk.com")
          _T(",uk.net,us.com,uy.com,za.com,dk.org,tel.no,fax.nr,")
          _T("mob.nr,mobil.nr,mobile.nr,tel.nr,tlf.nr,e164.arpa")
     ; // Ending Second Level TLDs
     // We get level 2 TLD from host name
     LPTSTR L2TLD=_tcschr(szHost,'.')+1;
     LPTSTR L2Pos=_tcsstr(szSLTLDs,L2TLD);
     // If level 2 TLD is not found in list then it is the
     // domain name
     if(!L2Pos){
          LPTSTR Host=_tcsdup(L2TLD);
          free(szPtrMark);
          return Host;
     }
     if((*(L2Pos+_tcslen(L2TLD))!=',') && (*(L2Pos+_tcslen(L2TLD))!='\0') && L2Pos!=szSLTLDs){
          // We just had an internal false-match
           LPTSTR Host=_tcsdup(L2TLD);
          free(szPtrMark);
          return Host;
     }
     LPTSTR Host=_tcsdup(szHost);
     free(szPtrMark);
     return Host;
}

It might not be the best …

… it might not be the fastest but it will suit any application that needs this conversion and it's UNICODE compatible. ;)

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" Converting A Host Name to a Domain Name in C++ : 5ubliminal's TellinYa "