c# - + string concat operator with a null operand -


a co-worker showed me strange behavior , i'd know if explain me why.

a basic constructor 2 string params:

    public myclass(string str1, string str2)     {         this.s1 = str1;         this.s2 = str2;         this.s3 = method(str2 + "._classname", str1);     }

method is:

public string method(string key, string defaultvalue) {     list<string> list = _vars[key];     if (list == null) return defaultvalue;     string res = "";     foreach (string s in list)     {         if (res != "") res += ",";         res += s;     }     return res; }

when ctor called within aspx page str2 null, works fine because if operand of string concatenation + null, empty string substituted.

but when ctor called str2 null in background thread, nullreferenceexception fired.

the problem solved testing str2 != null before using it, i'd know why same code fires exception, not!

here stack trace:

exception: system.nullreferenceexception  message: object reference not set instance of object. stacktrace:  @ myclass..ctor(string str1, string str2)  @ abandonedcartsnotificationjob.notifyabandonedcarts() in abandonedcartsnotificationjobpartial.cs:line 39  @ abandonedcartsnotificationjob.work() in abandonedcartsnotificationjob.cs:line 15  @ myruntime.jobmanager.run()  @ system.threading.threadhelper.threadstart_context(object state)  @ system.threading.executioncontext.runtrycode(object userdata)  @ system.runtime.compilerservices.runtimehelpers.executecodewithguaranteedcleanup(trycode code, cleanupcode backoutcode, object userdata)  @ system.threading.executioncontext.runinternal(executioncontext executioncontext, contextcallback callback, object state)  @ system.threading.executioncontext.run(executioncontext executioncontext, contextcallback callback, object state)  @ system.threading.threadhelper.threadstart()

there obscure bug in .net framework's implementation of string concatenation, affected concatenations of 4 objects, 1 of objects non-null and provided override of tostring returned null. situation isn't case here.

this situation caused 1 of following:

  • _vars null when method called
  • due misuse of _vars in multi-threaded application, internal state of _vars has been corrupted, resulting in nullreferenceexception when operator [] used.

Comments

Post a Comment

Popular posts from this blog

curl - PHP fsockopen help required -

i trying work on cloudflare api , have found in documentation. unfortunately have no idea how can use in fsockopen or through curl. here example of post request. need know how can make request below data post using curl or fsockopen curl https://www.cloudflare.com/api_json.html -d 'a=cache_lvl' \ -d 'tkn=8afbe6dea02407989af4dd4c97bb6e25' \ -d 'email=sample@example.com' \ -d 'z=example.com' \ -d 'v=agg' here link cloudflare https://www.cloudflare.com/docs/client-api.html#s4.2 try one: $ch = curl_init("https://www.cloudflare.com/api_json.html"); curl_setopt($ch, curlopt_returntransfer,1); curl_setopt($ch, curlopt_followlocation, 1); curl_setopt($ch, curlopt_ssl_verifypeer,false); // handling of -d curl parameter here. $param = array( 'a' => 'cache_lvl', 'tkn' => '8afbe6dea02407989af4dd4c97bb6e25', 'email' => 'sample@example.com', 'z' =...
Read more

HTTP/1.0 407 Proxy Authentication Required PHP -

i working in restricted network/limited access internet. since have use proxy make web service call. here php code calling web service , response . $client = new soapclient("http: //www.xyz.com/abc/wsdls/login.wsdl", array("trace" => 1, "exceptions" => 1, 'proxy_host' => $proxy_host, 'proxy_port' => $proxy_port, 'proxy_login' => $proxy_login, 'proxy_password' => $proxy_password)); response is fatal error: uncaught soapfault exception: [wsdl] soap-error: parsing wsdl: couldn't load ' http://www.xyz.com/abc/wsdls/login.wsdl ' : failed load external entity if copy url error message , paste in browser(with same proxy settings) works. 2nd scenario is, if pass values instead of variables giving me diffarant response $client = new soapclient("http: //www.xyz.com/abc/wsdls/login.wsdl", array("trace" => 1, "exceptions" => 1, 'proxy_host' ...
Read more

c# - Resource not found error -

i have problem accessing method on homecontroller. show code of method : [httpget] public actionresult decriptidentifiantetredirige(string login_crypter, string mdp_crypter) { string loginacrypter = _globalmanager.protegemotdepasse(login_crypter); string mdpacrypter = _globalmanager.protegemotdepasse(mdp_crypter); user userapp = new models.user(login_crypter, mdp_crypter); if (userapp.authentificationvalidee(userapp.userlogin, userapp.password)) { session["name"] = userapp.userlogin; return redirecttoaction("accueil", "home"); } else { return redirecttoaction("validerauthentification", "home"); } } then in routeconfig.cs wrote route : routes.maproute( name: "authentificationapresdecryptage", url: "{controller}/{action}/{login_crypter}/{mdp_crypter}", defaults: new...
Read more