c# - Why do 'Convert.ToInt32' and 'as int?' work differently? - 


convert.toint32(mycommand.executescalar()); // returns 100, because mycommand sql command gets non-null bigint cell mycommand.executescalar() int? ?? 0; //returns 0 when mycommand sql command gets non-null bigint cell

i have use second way in case, because mycommand.executescalar() can return dbnull. why second way return different result convert.toint32?

edit: thank you, all. changed type int64 , it's working now.

converting , casting (with cast operator, is operator , as operator) 2 different things:

  • convert changing 1 type type. string or int64 int32.
  • casting can done base type inheriting type. in case object int32. object must contain int32 succeed. in case not , cast return null.

in code:

int64 l = 100; object o = l; int32 i1 = o int32? ?? 0; // cast fails, "as" return 0. "??" make 0. int32 i2 = convert.toint32(o); // int32 inside object converted int32 , return 100.

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

javascript - jQuery .height() return 0 when visible but non-0 when hidden -

i have problem here right opposite others: in jquery cannot height of element when it's visible, when hidden. have html code: <div id="filtering-filter-holder"> <div id="filtering-filter-holder-inner"></div> </div> basic css it: #filtering-filter-holder { display: none; position: absolute; width: 420px; min-height: 100px; padding: 5px 5px 5px 5px; background-color: #ffffff; border: 1px solid #164372; } and finally, js in document.ready(): $('div.filtering-filter-headline').mouseenter(function() { var el = $(this).parent().find('div.filtering-filter-content'); if ($('div#filtering-filter-holder').is(':visible')) { $('div#filtering-filter-holder-inner').stop(true, true).fadeout(300, function() { $('div#filtering-filter-holder-inner').html($(el).html()); var height = $('div#filtering-filter-holder-inner&#
Read more