Featured post

c# - Usage of Server Side Controls in MVC Frame work -

-
i using asp.net 4.0 , mvc 2.0 web application. project requiremrnt have use server side control in application not possibl in noraml case. ideally want use adrotator control , datalist control. i saw few samples , references in codepleax mvc controllib howwver found less useful. can tell how utilize theese controls in asp.net application along mvc. note: please provide functionalities related adrotator , datalist controls not equivalent functionalities thanks in advace. mvc pages not use normal .net solution makes use of normal .net components impossible. a normal .net page use event driven solution call different methods service side mvc use actions , view completly different way handle things. also, mvc not use viewstate normal .net controlls require. found article discussing mixing of normal .net , mvc.
3 comments

c++ - Programmatically determine if std::string uses Copy-On-Write (COW) mechanism -

-

following on discussion question, wondering how 1 using native c++ determine programmatically whether or not std::string implementation using utilizes copy-on-write (cow)

i have following function:

#include <iostream> #include <string>  bool stdstring_supports_cow() {    //make sure string longer size of potential    //implementation of small-string.    std::string s1 = "012345678901234567890123456789"                     "012345678901234567890123456789"                     "012345678901234567890123456789"                     "012345678901234567890123456789"                     "012345678901234567890123456789";    std::string s2 = s1;    std::string s3 = s2;     bool result1 = (&s1[0]) == (&s2[0]);    bool result2 = (&s1[0]) == (&s3[0]);     s2[0] = 'x';     bool result3 = (&s1[0]) != (&s2[0]);    bool result4 = (&s1[0]) == (&s3[0]);     s3[0] = 'x';     bool result5 = (&s1[0]) != (&s3[0]);     return result1 && result2 &&           result3 && result4 &&           result5; }  int main() {   if (stdstring_supports_cow())       std::cout << "std::string cow." << std::endl;    else       std::cout << "std::string not cow." << std::endl;    return 0; }

the problem can't seem find c++ tool chain returns true. there flaw in assumption how cow implemented std::string?

update: based on kotlinski comments, i've changed use of writeble references data() in function, seems return "true" implementations.

bool stdstring_supports_cow() {    //make sure string longer size of potential    //implementation of small-string.    std::string s1 = "012345678901234567890123456789"                     "012345678901234567890123456789"                     "012345678901234567890123456789"                     "012345678901234567890123456789"                     "012345678901234567890123456789";    std::string s2 = s1;    std::string s3 = s2;     bool result1 = s1.data() == s2.data();    bool result2 = s1.data() == s3.data();     s2[0] = 'x';     bool result3 = s1.data() != s2.data();    bool result4 = s1.data() == s3.data();     s3[0] = 'x';     bool result5 = s1.data() != s3.data();     return result1 && result2 &&           result3 && result4 &&           result5; }

note: according n2668: "concurrency modifications basic string", in upcoming c++0x standard, cow option removed basic_string. james , beldaz bringing up.

using &s1[0] take adress not want, [0] returns writable reference , create copy.

use data() instead, returns const char*, , tests may pass.


Comments

Post a Comment

Popular posts from this blog

c# - Usage of Server Side Controls in MVC Frame work -

-
i using asp.net 4.0 , mvc 2.0 web application. project requiremrnt have use server side control in application not possibl in noraml case. ideally want use adrotator control , datalist control. i saw few samples , references in codepleax mvc controllib howwver found less useful. can tell how utilize theese controls in asp.net application along mvc. note: please provide functionalities related adrotator , datalist controls not equivalent functionalities thanks in advace. mvc pages not use normal .net solution makes use of normal .net components impossible. a normal .net page use event driven solution call different methods service side mvc use actions , view completly different way handle things. also, mvc not use viewstate normal .net controlls require. found article discussing mixing of normal .net , mvc.
Read more

ios - Very simple iPhone App crashes on UILabel settext -

-
i have simple application. have button , label in ib. have ibaction onclick calls settext on label. there's outlet label. connected in ib. crashes app first time in simulator. when launch again, sets text. crashes again next time. crashes on actual device. should simple, i'm not sure i'm doing wrong. thanks. in .h file : #import <uikit/uikit.h> @interface untitledviewcontroller : uiviewcontroller { iboutlet uilabel *label; iboutlet uibutton *button; } @property (nonatomic, retain) uilabel *label; -(ibaction) onclick1: (id) sender; @end and in .m: - (ibaction) onclick1: (id) sender { //[label settext:@"hello world!"]; label.text = @"hello world!"; //[button settitle:@"clicked" forstate:uicontrolstatenormal]; } sorry, i'm new site. how crash log , stack? thanks. edit : while answer technically correct, doesn't answer question @ :( sorry < warning - guess > if you're...
Read more

mysql - Why there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT clause? -

-
why there can 1 timestamp column current_timestamp in default or on update clause? create table `foo` ( `productid` int(10) unsigned not null, `addeddate` timestamp not null default current_timestamp, `updateddate` timestamp not null default current_timestamp on update current_timestamp ) engine=innodb; the error results: error code : 1293 incorrect table definition; there can 1 timestamp column current_timestamp in default or on update clause this limitation, due historical, code legacy reasons, has been lifted in recent versions of mysql: changes in mysql 5.6.5 (2012-04-10, milestone 8) previously, @ 1 timestamp column per table automatically initialized or updated current date , time. restriction has been lifted. timestamp column definition can have combination of default current_timestamp , on update current_timestamp clauses. in addition, these clauses can used datetime column definitions. more information, see automati...
Read more