dev c++ - Trying to open a file that doesn't exist prevents subsequent opening in dev-C++ -


i trying execute simple piece of code in dev-c++:

int fflag, num; char nomefile[40]; fstream str;  fflag=0; while (fflag==0)       {       cout<<"\nfile name? ";       cin>>nomefile;       str.open(nomefile,ios::in);        //checking if file exists       if (str)          {          fflag=1;          str>>num;             // reading value , sending standard output          cout<<num<<"\n";          }       else          {          cout<<"\nfile doesn't exist! ";          }        }

if try open existing file, there no problem. if try open file doesn't exist, receive error message (file doesn't exist) subsequent trial open existing file (i mean in same loop) fail producing same error message.

i tried add close instruction after detecting not-existing file, doesn't solve problem. don't understand! seems that, if try open not existing file, subsequent retrial (with str.open) returns null pointer, if file exists.

the same code execute correctly in code::blocks, should issue regarding dev-c++ or maybe problem of software portability.

any help? lot! giancarlo perlo - italy

failure open sets "fail" bit. these bits never(!) reset automatically, must reset them manually using clear(). bit counterintuitive considering fact opening new file should erase earlier history, consistent throughout iostream api.

in order fix this, move fstream loop though, each file gets opened new fstream instance. in general, should move declaration of variables close use possible. example, int fflag; should bool successful_read = false;, declared before loop. makes clearer how used. otoh, use endless loop break after reading file. further, use std::string name , use getline(std::cin, name) read file name.


Comments

Post a Comment

Popular posts from this blog

SPSS keyboard combination alters encoding -

my question not have programming practical issue on spss. accident keyword combination cannot remember because did not intend press changed encoding in spss , text in data in different language english shown small boxes. nevertheless, when kind of analysis performed different language text shown in output. does know reason? tried change encoding did not produce result. first, @ edit > options , see whether setting unicode or locale. might fix it. if have text in multiple languages, want unicode. otherwise, may have specific locale set wrong. can change set locale, need know locale want use.
Read more

Add new record to the table by click on the button in Microsoft Access -

in ms access form want implement separate button, adds new record table. in order added button , attached button event: private sub btnaddrec_click() refresh codecontextobject on error resume next docmd.gotorecord , , acnewrec if err.number <> 0 btnaddrec.enabled = false end if end end sub everything ok when open window , click btnaddrec button, problem when first of perform navigation through existed records , after click on button. got runtime error: 2105: «you can't go specified record. may @ end of recordset» . how solve issue, need have ability add new record on click on specific button, no matter, have walked or not walked through records before. thanks. i created simple form field call description (and autonumber) , created button code follows click event. filled number of records , navigated through them, clicked addnewrec button. form navigated new record without issues. able click addnewrec button directly after ...
Read more

CSS3 Transition to highlight new elements created in JQuery -

i want use css3 color transition apply highlight-fading color effect (yellow transparent) new elements appended markup using jquery. css #content div { background-color:transparent; -moz-transition:background-color 2s; -webkit-transition:background-color 2s; -o-transition:background-color 2s; transition:background-color 2s; } #content div.new { background-color:yellow; } html <div id="content"></div> <a id="add-element" href="#">add new element</a> js $('#add-element').click(function() { var newelement = $('<div class="new">new element</div>'); $('#content').append(newelement); newelement.removeclass('new'); }); when click link, new element created. class "new" (background color yellow) , it's appended html markup. should able remove "new" class trigger background color transition transparent (or whate...
Read more