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  • Why first arg to execve() must be path to executable

    - by EBM
    I understand that execve() and family require the first argument of its argument array to be the same as the executable that is also pointed to by its first argument. That is, in this: execve(prog, args, env); args[0] will usually be the same as prog. But I can't seem to find information as to why this is. I also understand that executables (er, at least shell scripts) always have their calling path as the first argument when running, but I would think that the shell would do the work to put it there, and execve() would just call the executable using the path given in its first argument ("prog" from above), then passing the argument array ("args" from above) as one would on the command line.... i.e., I don't call scripts on the command line with a duplicate executable path in the args list.... /bin/ls /bin/ls /home/john Can someone explain?

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  • run shell command from java

    - by Aykut
    Hi, I am working on an application an have an issue about running shell command from java application. here is the code: public String execRuntime(String cmd) { Process proc = null; int inBuffer, errBuffer; int result = 0; StringBuffer outputReport = new StringBuffer(); StringBuffer errorBuffer = new StringBuffer(); try { proc = Runtime.getRuntime().exec(cmd); } catch (IOException e) { return ""; } try { response.status = 1; result = proc.waitFor(); } catch (InterruptedException e) { return ""; } if (proc != null && null != proc.getInputStream()) { InputStream is = proc.getInputStream(); InputStream es = proc.getErrorStream(); OutputStream os = proc.getOutputStream(); try { while ((inBuffer = is.read()) != -1) { outputReport.append((char) inBuffer); } while ((errBuffer = es.read()) != -1) { errorBuffer.append((char) errBuffer); } } catch (IOException e) { return ""; } try { is.close(); is = null; es.close(); es = null; os.close(); os = null; } catch (IOException e) { return ""; } proc.destroy(); proc = null; } if (errorBuffer.length() > 0) { logger .error("could not finish execution because of error(s)."); logger.error("*** Error : " + errorBuffer.toString()); return ""; } return outputReport.toString(); } but when i try to exec command like : /export/home/test/myapp -T "some argument" myapp reads "some argument" as two seperated arguments.but I want to read "some argument" as only a argument. when i directly run this command from terminal, it executed successfully. I tried '"some argument"' ,""some argument"" , "some\ argument" but did not work for me. how can i read this argument as one argument. Thnaks.

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  • Getting time in ubuntu

    - by user2578666
    include #include <stdio.h> int GetTime() { struct timespec tsp; clock_gettime(CLOCK_REALTIME, &tsp); //Call clock_gettime to fill tsp fprintf(stdout, "time=%d.%d\n", tsp.tv_sec, tsp.tv_nsec); fflush(stdout); } I am trying to compile the above code but it keeps throwing the error: time.c: In function ‘GetTime’: time.c:12:4: warning: implicit declaration of function ‘clock_gettime’ [-Wimplicit-function-declaration] time.c:12:18: error: ‘CLOCK_REALTIME’ undeclared (first use in this function) time.c:12:18: note: each undeclared identifier is reported only once for each function it appears in time.c:14:4: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘__time_t’ [-Wformat] time.c:14:4: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘long int’ [-Wformat] I have tried compiling with -lrt flag and -std=gnu99. Nothing works.

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  • Cannot obtain value of local or argument 'hwndSource' as it is not available at this instruction poi

    - by Dänu
    Hey Guys I'm playing around with Interops and I thought: "Hey let's code something that accesses the clipboard ..." so I googled and found some articles (yeah I'm doing it with WPF - .Net 3.5). However the following method generates an error (as seen in the title) and throws a stackoverflow. private void Window_SourceInitialized(object sender, EventArgs e) { // Hook to Clipboard base.OnSourceInitialized(e); HwndSource hwndSource = PresentationSource.FromVisual(this) as HwndSource; if (hwndSource != null) { installedHandle = hwndSource.Handle; viewerHandle = SetClipboardViewer(installedHandle); hwndSource.AddHook(new HwndSourceHook(this.hwndSourceHook)); } // End Hook to Clipboard } I have (really) no idea what's going on there. Any Ideas?

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  • Customize Team Build 2010 – Part 16: Specify the relative reference path

    In the series the following parts have been published Part 1: Introduction Part 2: Add arguments and variables Part 3: Use more complex arguments Part 4: Create your own activity Part 5: Increase AssemblyVersion Part 6: Use custom type for an argument Part 7: How is the custom assembly found Part 8: Send information to the build log Part 9: Impersonate activities (run under other credentials) Part 10: Include Version Number in the Build Number Part 11: Speed up opening my build process template Part 12: How to debug my custom activities Part 13: Get control over the Build Output Part 14: Execute a PowerShell script Part 15: Fail a build based on the exit code of a console application Part 16: Specify the relative reference path As I have already blogged about, it is not intuitive how to specify the paths where the build server has to look for references that are stored in Source Control. It is a common practice to store 3rd party libraries in Source Control, so they are available to everyone, everyone uses the same version of the libraries and updating a library can be done centrally. In Team Build 2010 these paths are specified as a parameter for MSBuild. What we will do in this post is building the values for this parameter based on the values in an argument. You are now pretty aware how to customize the build template, so let’s do the modifications in another way. Instead of opening the xaml file in the workflow designer, we open it in the XML editor. You can open it in the XML Editor by either selecting the Open with menu (see the context menu), or by choosing the View code option. To add this functionality we need to: Specify a new argument Add the argument to the metadata Build the absolute paths for the references and add these paths to the MSBuild arguments 1. Specify a new argument Locate at the top of the document the Members (which are the arguments) of the XAML and add the following line <x:Property Name="ReferencePaths" Type="InArgument(s:String[])" /> 2. Add the argument to the metadata Then locate the line <mtbw:ProcessParameterMetadataCollection> and paste the following line <mtbw:ProcessParameterMetadata Category="Misc" Description="The list of reference paths, relative to the root path in the Workspace mapping." DisplayName="Reference paths" ParameterName="ReferencePaths" /> 3. Build the absolute paths for the references and add these paths to the MSBuild arguments Now locate the place where the assignments are done to the variables used in the agent. And add the following lines after the last Assign activity         <Sequence DisplayName="Initialize ReferencePath" sap:VirtualizedContainerService.HintSize="464,428">           <Sequence.Variables>             <Variable x:TypeArguments="x:String" Name="ReferencePathsArgument">               <Variable.Default>                 <Literal x:TypeArguments="x:String" Value="" />               </Variable.Default>             </Variable>           </Sequence.Variables>           <sap:WorkflowViewStateService.ViewState>             <scg:Dictionary x:TypeArguments="x:String, x:Object">               <x:Boolean x:Key="IsExpanded">True</x:Boolean>             </scg:Dictionary>           </sap:WorkflowViewStateService.ViewState>           <ForEach x:TypeArguments="x:String" DisplayName="Iterate through the paths" sap:VirtualizedContainerService.HintSize="287,206" mtbwt:BuildTrackingParticipant.Importance="Low" Values="[ReferencePaths]">             <ActivityAction x:TypeArguments="x:String">               <ActivityAction.Argument>                 <DelegateInArgument x:TypeArguments="x:String" Name="path" />               </ActivityAction.Argument>               <Assign x:TypeArguments="x:String" DisplayName="Build ReferencePath argument" sap:VirtualizedContainerService.HintSize="257,100" mtbwt:BuildTrackingParticipant.Importance="Low"  To="[ReferencePathsArgument]" Value="[If(String.IsNullOrEmpty(ReferencePathsArgument), &quot;&quot;, ReferencePathsArgument + &quot;;&quot;) + IO.Path.Combine(SourcesDirectory, path)]" />             </ActivityAction>           </ForEach>           <Assign DisplayName="Append the reference paths to the MSBuild Arguments" sap:VirtualizedContainerService.HintSize="287,58">             <Assign.To>               <OutArgument x:TypeArguments="x:String">[MSBuildArguments]</OutArgument>             </Assign.To>             <Assign.Value>               <InArgument x:TypeArguments="x:String">[String.Format("{0} /p:ReferencePath=""{1}""", MSBuildArguments, ReferencePathsArgument)]</InArgument>             </Assign.Value>           </Assign>         </Sequence> Now you can use the template to specify the paths relative to SourcesDirectory. You can download the full solution at BuildProcess.zip. It will include the sources of every part and will continue to evolve.

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  • Wrapping ASP.NET Client Callbacks

    - by Ricardo Peres
    Client Callbacks are probably the less known (and I dare say, less loved) of all the AJAX options in ASP.NET, which also include the UpdatePanel, Page Methods and Web Services. The reason for that, I believe, is it’s relative complexity: Get a reference to a JavaScript function; Dynamically register function that calls the above reference; Have a JavaScript handler call the registered function. However, it has some the nice advantage of being self-contained, that is, doesn’t need additional files, such as web services, JavaScript libraries, etc, or static methods declared on a page, or any kind of attributes. So, here’s what I want to do: Have a DOM element which exposes a method that is executed server side, passing it a string and returning a string; Have a server-side event that handles the client-side call; Have two client-side user-supplied callback functions for handling the success and error results. I’m going to develop a custom control without user interface that does the registration of the client JavaScript method as well as a server-side event that can be hooked by some handler on a page. My markup will look like this: 1: <script type="text/javascript"> 1:  2:  3: function onCallbackSuccess(result, context) 4: { 5: } 6:  7: function onCallbackError(error, context) 8: { 9: } 10:  </script> 2: <my:CallbackControl runat="server" ID="callback" SendAllData="true" OnCallback="OnCallback"/> The control itself looks like this: 1: public class CallbackControl : Control, ICallbackEventHandler 2: { 3: #region Public constructor 4: public CallbackControl() 5: { 6: this.SendAllData = false; 7: this.Async = true; 8: } 9: #endregion 10:  11: #region Public properties and events 12: public event EventHandler<CallbackEventArgs> Callback; 13:  14: [DefaultValue(true)] 15: public Boolean Async 16: { 17: get; 18: set; 19: } 20:  21: [DefaultValue(false)] 22: public Boolean SendAllData 23: { 24: get; 25: set; 26: } 27:  28: #endregion 29:  30: #region Protected override methods 31:  32: protected override void Render(HtmlTextWriter writer) 33: { 34: writer.AddAttribute(HtmlTextWriterAttribute.Id, this.ClientID); 35: writer.RenderBeginTag(HtmlTextWriterTag.Span); 36:  37: base.Render(writer); 38:  39: writer.RenderEndTag(); 40: } 41:  42: protected override void OnInit(EventArgs e) 43: { 44: String reference = this.Page.ClientScript.GetCallbackEventReference(this, "arg", "onCallbackSuccess", "context", "onCallbackError", this.Async); 45: String script = String.Concat("\ndocument.getElementById('", this.ClientID, "').callback = function(arg, context, onCallbackSuccess, onCallbackError){", ((this.SendAllData == true) ? "__theFormPostCollection.length = 0; __theFormPostData = ''; WebForm_InitCallback(); " : String.Empty), reference, ";};\n"); 46:  47: this.Page.ClientScript.RegisterStartupScript(this.GetType(), String.Concat("callback", this.ClientID), script, true); 48:  49: base.OnInit(e); 50: } 51:  52: #endregion 53:  54: #region Protected virtual methods 55: protected virtual void OnCallback(CallbackEventArgs args) 56: { 57: EventHandler<CallbackEventArgs> handler = this.Callback; 58:  59: if (handler != null) 60: { 61: handler(this, args); 62: } 63: } 64:  65: #endregion 66:  67: #region ICallbackEventHandler Members 68:  69: String ICallbackEventHandler.GetCallbackResult() 70: { 71: CallbackEventArgs args = new CallbackEventArgs(this.Context.Items["Data"] as String); 72:  73: this.OnCallback(args); 74:  75: return (args.Result); 76: } 77:  78: void ICallbackEventHandler.RaiseCallbackEvent(String eventArgument) 79: { 80: this.Context.Items["Data"] = eventArgument; 81: } 82:  83: #endregion 84: } And the event argument class: 1: [Serializable] 2: public class CallbackEventArgs : EventArgs 3: { 4: public CallbackEventArgs(String argument) 5: { 6: this.Argument = argument; 7: this.Result = String.Empty; 8: } 9:  10: public String Argument 11: { 12: get; 13: private set; 14: } 15:  16: public String Result 17: { 18: get; 19: set; 20: } 21: } You will notice two properties on the CallbackControl: Async: indicates if the call should be made asynchronously or synchronously (the default); SendAllData: indicates if the callback call will include the view and control state of all of the controls on the page, so that, on the server side, they will have their properties set when the Callback event is fired. The CallbackEventArgs class exposes two properties: Argument: the read-only argument passed to the client-side function; Result: the result to return to the client-side callback function, set from the Callback event handler. An example of an handler for the Callback event would be: 1: protected void OnCallback(Object sender, CallbackEventArgs e) 2: { 3: e.Result = String.Join(String.Empty, e.Argument.Reverse()); 4: } Finally, in order to fire the Callback event from the client, you only need this: 1: <input type="text" id="input"/> 2: <input type="button" value="Get Result" onclick="document.getElementById('callback').callback(callback(document.getElementById('input').value, 'context', onCallbackSuccess, onCallbackError))"/> The syntax of the callback function is: arg: some string argument; context: some context that will be passed to the callback functions (success or failure); callbackSuccessFunction: some function that will be called when the callback succeeds; callbackFailureFunction: some function that will be called if the callback fails for some reason. Give it a try and see if it helps!

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  • How to create a custom "render :my_format => argument" in rails 2.3(.5)?

    - by Rafael
    Hey! I would like to create a custom render as specified in title. For instance, I have my controller: class MyController < ApplicationController def index respond_to do |format| format.html # index.html.erb format.xml { render :xml => @objs } end end end , but I would like something like this: class MyController < ApplicationController def index respond_to do |format| format.html # index.html.erb format.xml { render :xml => @objs } format.my_format { render :my_format => @objs } end end end Is it possible? What are the steps I need to make it work? Thanks in advance!

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  • How to override a render to create a custom "render :my_format => argument" in rails 2.3(.5)?

    - by Rafael
    Hey! I would like to create a custom render as specified in title. For instance, I have my controller: class MyController < ApplicationController def index respond_to do |format| format.html # index.html.erb format.xml { render :xml => @objs } end end end , but I would like something like this: class MyController < ApplicationController def index respond_to do |format| format.html # index.html.erb format.xml { render :xml => @objs } format.my_format { render :my_format => @objs } end end end Is it possible? What are the steps I need to make it work? Thanks in advance! UPDATE I want something like in here. So I replaced the @objs with a method but it didn't work either (the method wasn't called). Obs: I register the mime type at config/initializers/mime_types.rb.

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  • Android java.lang.VerifyError for private method with annotated argument.

    - by alex2k8
    I have a very simple project that compiles, but can't be started on Emulator. The problem is with this method: private void bar(@Some String a) {} // java.lang.VerifyError The issue can be avoided if annotation removed private void bar(String a) {} // OK or the method visibility changed: void bar(@Some String a) {} // OK public void bar(@Some String a) {} // OK protected void bar(@Some String a) {} // OK Any idea what is wrong with original method? Is this a dalvik bug, or? If some one whould like to experiment with code, here it is: Test.java: public class Test { private void bar(@Some String a) {} public void foo() { bar(null); } } Some.java: public @interface Some {} MainActivity.java: public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); new Test().foo(); } } Stack trace: ERROR/dalvikvm(1358): Could not find method com.my.Test.bar, referenced from method com.my.Test.foo WARN/dalvikvm(1358): VFY: unable to resolve direct method 11: Lcom/my/Test;.bar (Ljava/lang/String;)V WARN/dalvikvm(1358): VFY: rejecting opcode 0x70 at 0x0001 WARN/dalvikvm(1358): VFY: rejected Lcom/my/Test;.foo ()V WARN/dalvikvm(1358): Verifier rejected class Lcom/my/Test; DEBUG/AndroidRuntime(1358): Shutting down VM WARN/dalvikvm(1358): threadid=3: thread exiting with uncaught exception (group=0x4000fe70) ERROR/AndroidRuntime(1358): Uncaught handler: thread main exiting due to uncaught exception ERROR/AndroidRuntime(1358): java.lang.VerifyError: com.my.Test ERROR/AndroidRuntime(1358): at com.my.MainActivity.onCreate(MainActivity.java:13) ERROR/AndroidRuntime(1358): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123) ERROR/AndroidRuntime(1358): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2231) ERROR/AndroidRuntime(1358): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2284) ERROR/AndroidRuntime(1358): at android.app.ActivityThread.access$1800(ActivityThread.java:112) ERROR/AndroidRuntime(1358): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1692) ERROR/AndroidRuntime(1358): at android.os.Handler.dispatchMessage(Handler.java:99) ERROR/AndroidRuntime(1358): at android.os.Looper.loop(Looper.java:123) ERROR/AndroidRuntime(1358): at android.app.ActivityThread.main(ActivityThread.java:3948) ERROR/AndroidRuntime(1358): at java.lang.reflect.Method.invokeNative(Native Method) ERROR/AndroidRuntime(1358): at java.lang.reflect.Method.invoke(Method.java:521) ERROR/AndroidRuntime(1358): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:782) ERROR/AndroidRuntime(1358): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540) ERROR/AndroidRuntime(1358): at dalvik.system.NativeStart.main(Native Method)

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  • How can I modify complex command-line argument strings in Perl?

    - by mmccoo
    I have a command line that I'm trying to modify to remove some of the arguments. What makes this complex is that I can have nested arguments. Say that I have this: $cmdline = "-a -xyz -a- -b -xyz -b- -a -xyz -a-" I have three different -xyz flags that are to be interpreted in two different contexts. One is the -a context and the other is the -b context. I want to remove the "a" -xyz's but leave the ones in the "b" -xyz. in the above case, I want: -a -a- -b -xyz -b- -a -a- Alternately, if I have: -a -123 -a- -b -xyz -b- -a -xyz -a-" I want: -a -123 -a- -a -xyz -a- -b -xyz -b- -a -a- It's this second case that I'm stuck on. How can I most effectively do this in Perl?

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  • Pythonika installation error on ubuntu 12

    - by user1426913
    I have been following links: to install pythonika on ubuntu: How to install Pythonika on Ubuntu? I get error: $ sudo make -f Makefile.linux cc -c Pythonika.c -I/usr/local/Wolfram/Mathematica/9.0/SystemFiles/Links/MathLink/DeveloperKit/Linux/CompilerAdditions -I/usr/include/python2.7/ Pythonika.c: In function ‘PyUnicodeString’: Pythonika.c:109:5: warning: passing argument 1 of ‘PyUnicodeUCS4_FromUnicode’ from incompatible pointer type [enabled by default] /usr/include/python2.7/unicodeobject.h:464:23: note: expected ‘const Py_UNICODE *’ but argument is of type ‘short unsigned int *’ Pythonika.c: In function ‘python_to_mathematica_object’: Pythonika.c:411:13: warning: passing argument 2 of ‘MLPutUnicodeString’ from incompatible pointer type [enabled by default] /usr/local/Wolfram/Mathematica/9.0/SystemFiles/Links/MathLink/DeveloperKit/Linux/CompilerAdditions/mathlink.h:4299:1: note: expected ‘const short unsigned int *’ but argument is of type ‘Py_UNICODE ’ "/usr/local/Wolfram/Mathematica/9.0/SystemFiles/Links/MathLink/DeveloperKit/Linux/CompilerAdditions/mprep" Pythonika.tm -o Pythonikatm.c /bin/sh: 1: /usr/local/Wolfram/Mathematica/9.0/SystemFiles/Links/MathLink/DeveloperKit/Linux/CompilerAdditions/mprep: not found make: ** [Pythonikatm.o] Error 127

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  • How should I check that a given argument is a datetime.date object?

    - by rmh
    I'm currently using an assert statement with isinstance. Because datetime is a subclass of date, I also need to check that it isn't an instance of datetime. Surely there's a better way? from datetime import date, datetime def some_func(arg): assert isinstance(arg, date) and not isinstance(arg, datetime),\ 'arg must be a datetime.date object' # ...

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  • How do I handle a missing mandatory argument in Ruby OptionParser?

    - by Rob Jones
    In OptionParser I can make an option mandatory, but if I leave out that value it will take the name of any following option as the value, screwing up the rest of the command line parsing. Here is a test case that echoes the values of the options: $ ./test_case.rb --input foo --output bar output bar input foo Now leave out the value for the first option: $ ./test_case.rb --input --output bar input --output Is there some way to prevent it taking another option name as a value? Thanks! Here is the test case code: #!/usr/bin/env ruby require 'optparse' files = Hash.new option_parser = OptionParser.new do |opts| opts.on('-i', '--input FILENAME', 'Input filename - required') do |filename| files[:input] = filename end opts.on('-o', '--output FILENAME', 'Output filename - required') do |filename| files[:output] = filename end end begin option_parser.parse!(ARGV) rescue OptionParser::ParseError $stderr.print "Error: " + $! + "\n" exit end files.keys.each do |key| print "#{key} #{files[key]}\n" end

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  • Preffered lambda syntax?

    - by Roger Alsing
    I'm playing around a bit with my own C like DSL grammar and would like some oppinions. I've reserved the use of "(...)" for invocations. eg: foo(1,2); My grammar supports "trailing closures" , pretty much like Ruby's blocks that can be passed as the last argument of an invocation. Currently my grammar support trailing closures like this: foo(1,2) { //parameterless closure passed as the last argument to foo } or foo(1,2) [x] { //closure with one argument (x) passed as the last argument to foo print (x); } The reason why I use [args] instead of (args) is that (args) is ambigious: foo(1,2) (x) { } There is no way in this case to tell if foo expects 3 arguments (int,int,closure(x)) or if foo expects 2 arguments and returns a closure with one argument(int,int) - closure(x) So thats pretty much the reason why I use [] as for now. I could change this to something like: foo(1,2) : (x) { } or foo(1,2) (x) -> { } So the actual question is, what do you think looks best? [...] is somewhat wrist unfriendly. let x = [a,b] { } Ideas?

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  • Can't understand example using continuations

    - by Matt Fenwick
    I'm reading the r6rs Scheme report and am confused by the explanation of continuations (I find it to be too dense and lacking of examples for a beginner). What is this code doing and how does it evaluate to 4? Why does call/cc want an argument that's a function of one argument? How is call/cc's argument used? (+ 1 (call-with-current-continuation (lambda (escape) (+ 2 (escape 3))))) =? 4 This example is from section 1.11 - Continuations.

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  • What is the best way to marshal a char array function argument?

    - by Seh Hui 'Felix' Leong
    Let say that given the following signature in LegacyLib.dll: int Login(SysInst *inst, char username[8], char password[6]); The simple way to marshal this function in C# would be: [DllImport("LegacyLib.dll", CharSet=CharSet.Ansi)] public static extern int Login(ref SysInst inst, string username, string password); The problem of doing it in a such a naive way is that the managed string we passed into the username or password parameter could be longer than the array bounds and this could potentially cause a buffer overrun in LegacyLib.dll. Is there a better way which overcomes this problem? i.e. is there any quick [MarshalAs(…)] magic that I could use to counter that?

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  • How do I use a variable argument number in a bash script?

    - by Corbin Tarrant
    #!/bin/bash # Script to output the total size of requested filetype recursively # Error out if no file types were provided if [ $# -lt 1 ] then echo "Syntax Error, Please provide at least one type, ex: sizeofTypes {filetype1} {filetype2}" exit 0 fi #set first filetype types="-name *."$1 #loop through additional filetypes and append num=1 while [ $num -lt $# ] do (( num++ )) types=$types' -o -name *.'$$num done echo "TYPES="$types find . -name '*.'$1 | xargs du -ch *.$1 | grep total The problem I'm having is right here: #loop through additional filetypes and append num=1 while [ $num -lt $# ] do (( num++ )) types=$types' -o -name *.'>>$$num<< done I simply want to iterate over all the arguments not including the first one, should be easy enough, but I'm having a difficult time figuring out how to make this work

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  • Liskov principle: violation by type-hinting

    - by Elias Van Ootegem
    According to the Liskov principle, a construction like the one below is invalid, as it strengthens a pre-condition. I know the example is pointless/nonsense, but when I last asked a question like this, and used a more elaborate code sample, it seemed to distract people too much from the actual question. //Data models abstract class Argument { protected $value = null; public function getValue() { return $this->value; } abstract public function setValue($val); } class Numeric extends Argument { public function setValue($val) { $this->value = $val + 0;//coerce to number return $this; } } //used here: abstract class Output { public function printValue(Argument $arg) { echo $this->format($arg); return $this; } abstract public function format(Argument $arg); } class OutputNumeric extends Output { public function format(Numeric $arg)//<-- VIOLATION! { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } My question is this: Why would this kind of "violation" be considered harmful? So much so that some languages, like the one I used in this example (PHP), don't even allow this? I'm not allowed to strengthen the type-hint of an abstract method but, by overriding the printValue method, I am allowed to write: class OutputNumeric extends Output { final public function printValue(Numeric $arg) { echo $this->format($arg); } public function format(Argument $arg) { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } But this would imply repeating myself for each and every child of Output, and makes my objects harder to reuse. I understand why the Liskov principle exists, don't get me wrong, but I find it somewhat difficult to fathom why the signature of an abstract method in an abstract class has to be adhered to so much stricter than a non-abstract method. Could someone explain to me why I'm not allowed to hind at a child class, in a child class? The way I see it, the child class OutputNumeric is a specific use-case of Output, and thus might need a specific instance of Argument, namely Numeric. Is it really so wrong of me to write code like this?

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  • SQL efficiency argument, add a column or solvable by query?

    - by theTurk
    I am a recent college graduate and a new hire for software development. Things have been a little slow lately so I was given a db task. My db skills are limited to pet projects with Rails and Django. So, I was a little surprised with my latest task. I have been asked by my manager to subclass Person with a 'Parent' table and add a reference to their custodian in the Person table. This is to facilitate going from Parent to Form when the custodian, not the Parent, is the FormContact. Here is a simplified, mock structure of a sql-db I am working with. I would have drawn the relationship tables if I had access to Visio. We have a table 'Person' and we have a table 'Form'. There is a table, 'FormContact', that relates a Person to a Form, not all Persons are related to a Form. There is a relationship table for Person to Person relationships (Employer, Parent, etc.) I've asked, "Why this couldn't be handled by a query?" Response, Inefficient. (Really!?!) So, I ask, "Why not have a reference to the Form? That would be more efficient since you wouldn't be querying the FormContacts table with the reference from child/custodian." Response, this would essentially make the Parent is a FormContact. (Fair enough.) I went ahead an wrote a query to get from non-FormContact Parent to Form, and tested on the production server. The response time was instantaneous. *SOME_VALUE* is the Parent's fk ID. SELECT FormID FROM FormContact WHERE FormContact.ContactID IN (SELECT SourceContactID FROM ContactRelationship WHERE (ContactRelationship.RelatedContactID = *SOME_VALUE*) AND (ContactRelationship.Relationship = 'Parent')); If I am right, "This is an unnecessary change." What should I do, defend my position or should I concede to the managers request? If I am wrong. What is my error? Is there a better solution than the manager's?

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  • How can I pipe a large amount of data as a runtime argument?

    - by Zombies
    Running an executable JAR on a linux platform here. The program it self works on a somewhat large amount of data, basically a list of URLs... could be up to 2k. Currently I get this from a simple DB call. But I was thinking that instead of creating a new mode and writing SQL to get a new result set and having to redploy everytime, I could just make the program more robust by passing in the result set (the list of URLs) that need to be worked on... so, within a linux environment, is there a pain-free/simple way to get the result set and pass it in dynamically? I know file i/o is one, but it doesn't seem to be effecient because each file has to be named, as well more logic to handle grabbing the correct file, creating a file with a unique name, etc.

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  • How to create a closure and pass in variable length argument list?

    - by Jian Lin
    We can create a closure p by capturing the arguments in the scope in the following code: var p = function() { }; if (typeof(console) != 'undefined' && console.log) { p = function() { console.log(arguments); }; } but the arguments are passed like an array to console.log, instead of passed one by one as in console.log(arguments[0], arguments[1], arguments[2], ... Is there a way to expand the arguments and pass to console.log like the way above? Note that p = console.log; works well in Firefox and IE 8 but not on Chrome.

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  • Singular method name for single object argument, plural for a list?

    - by nasufara
    I'm having a problem with naming a method for a database application. In my Database instance, I have a method that can remove an Agreement object from the database. However, I want to be able to remove multiple Agreements at once, to be able to use transactions. The problem is that I also have an overload to remove a single Agreement object. Essentially, my structure is like this: public class Database { // ... public void RemoveAgreement(Agreement a) { // ... } public void RemoveAgreement(IEnumerable<Agreement> agreements) { // ... } } But this can be confusing, as the overload with the list of Agreements has a singular name, despite being inherently plural. My question is, how should I structure this? Should I have two overloads with the name RemoveAgreement(), or RemoveAgreements()? Or should I use two separate methods, instead of overloads? Thanks.

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  • Preferred lambda syntax?

    - by Roger Alsing
    I'm playing around a bit with my own C like DSL grammar and would like some oppinions. I've reserved the use of "(...)" for invocations. eg: foo(1,2); My grammar supports "trailing closures" , pretty much like Ruby's blocks that can be passed as the last argument of an invocation. Currently my grammar support trailing closures like this: foo(1,2) { //parameterless closure passed as the last argument to foo } or foo(1,2) [x] { //closure with one argument (x) passed as the last argument to foo print (x); } The reason why I use [args] instead of (args) is that (args) is ambigious: foo(1,2) (x) { } There is no way in this case to tell if foo expects 3 arguments (int,int,closure(x)) or if foo expects 2 arguments and returns a closure with one argument(int,int) - closure(x) So thats pretty much the reason why I use [] as for now. I could change this to something like: foo(1,2) : (x) { } or foo(1,2) (x) -> { } So the actual question is, what do you think looks best? [...] is somewhat wrist unfriendly. let x = [a,b] { } Ideas?

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