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  • C/C++: Passing a structure by value, with another structure as one of its members, changes values of

    - by jellyfisharepretty
    Sorry for the confusing title, but it basically says it all. Here's the structures I'm using (found in OpenCV) : struct CV_EXPORTS CvRTParams : public CvDTreeParams { bool calc_var_importance; int nactive_vars; CvTermCriteria term_crit; CvRTParams() : CvDTreeParams( 5, 10, 0, false, 10, 0, false, false, 0 ), calc_var_importance(false), nactive_vars(0) { term_crit = cvTermCriteria( CV_TERMCRIT_ITER+CV_TERMCRIT_EPS, 50, 0.1 ); } } and typedef struct CvTermCriteria { int type; int max_iter; double epsilon; } CvTermCriteria; CV_INLINE CvTermCriteria cvTermCriteria( int type, int max_iter, double epsilon ) { CvTermCriteria t; t.type = type; t.max_iter = max_iter; t.epsilon = (float)epsilon; return t; } Now, I initialize a CvRTParams structure and set values for its members : CvRTParams params; params.max_depth = 8; params.min_sample_count = 10; params.regression_accuracy = 0; params.use_surrogates = false; params.max_categories = 10; params.priors = priors; params.calc_var_importance = true; params.nactive_vars = 9; params.term_crit.max_iter = 33; params.term_crit.epsilon = 0.1; params.term_crit.type = 3; Then call a function of an object, taking params in as a parameter : CvRTrees* rt = new CvRTrees; rt->train(t, CV_ROW_SAMPLE, r, 0, 0, var_type, 0, params) What happens now ? Values of... params.term_crit.max_iter params.term_crit.epsilon params.term_crit.type have changed ! They are no longer 33, 0.1 and 3, but something along the lines of 3, 7.05541e-313 and 4, and this, for the whole duration of the CvRtrees::train() function...

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  • What happens to class members when malloc is used instead of new?

    - by Felix
    I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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  • How to make 2 incompatible types, but with the same members, interchangeable?

    - by Quigrim
    Yesterday 2 of the guys on our team came to me with an uncommon problem. We are using a third-party component in one of our winforms applications. All the code has already been written against it. They then wanted to incorporate another third-party component, by the same vender, into our application. To their delight they found that the second component had the exact same public members as the first. But to their dismay, the 2 components have completely separate inheritance hierarchies, and implement no common interfaces. Makes you wonder... Well, makes me wonder. An example of the problem: public class ThirdPartyClass1 { public string Name { get { return "ThirdPartyClass1"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass1 is doing its thing."); } } public class ThirdPartyClass2 { public string Name { get { return "ThirdPartyClass2"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass2 is doing its thing."); } } Gladly they felt copying and pasting the code they wrote for the first component was not the correct answer. So they were thinking of assigning the component instant into an object reference and then modifying the code to do conditional casts after checking what type it was. But that is arguably even uglier than the copy and paste approach. So they then asked me if I can write some reflection code to access the properties and call the methods off the two different object types since we know what they are, and they are exactly the same. But my first thought was that there goes the elegance. I figure there has to be a better, graceful solution to this problem.

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  • A ToDynamic() Extension Method For Fluent Reflection

    - by Dixin
    Recently I needed to demonstrate some code with reflection, but I felt it inconvenient and tedious. To simplify the reflection coding, I created a ToDynamic() extension method. The source code can be downloaded from here. Problem One example for complex reflection is in LINQ to SQL. The DataContext class has a property Privider, and this Provider has an Execute() method, which executes the query expression and returns the result. Assume this Execute() needs to be invoked to query SQL Server database, then the following code will be expected: using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // Executes the query. Here reflection is required, // because Provider, Execute(), and ReturnValue are not public members. IEnumerable<Product> results = database.Provider.Execute(query.Expression).ReturnValue; // Processes the results. foreach (Product product in results) { Console.WriteLine("{0}, {1}", product.ProductID, product.ProductName); } } Of course, this code cannot compile. And, no one wants to write code like this. Again, this is just an example of complex reflection. using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // database.Provider PropertyInfo providerProperty = database.GetType().GetProperty( "Provider", BindingFlags.NonPublic | BindingFlags.GetProperty | BindingFlags.Instance); object provider = providerProperty.GetValue(database, null); // database.Provider.Execute(query.Expression) // Here GetMethod() cannot be directly used, // because Execute() is a explicitly implemented interface method. Assembly assembly = Assembly.Load("System.Data.Linq"); Type providerType = assembly.GetTypes().SingleOrDefault( type => type.FullName == "System.Data.Linq.Provider.IProvider"); InterfaceMapping mapping = provider.GetType().GetInterfaceMap(providerType); MethodInfo executeMethod = mapping.InterfaceMethods.Single(method => method.Name == "Execute"); IExecuteResult executeResult = executeMethod.Invoke(provider, new object[] { query.Expression }) as IExecuteResult; // database.Provider.Execute(query.Expression).ReturnValue IEnumerable<Product> results = executeResult.ReturnValue as IEnumerable<Product>; // Processes the results. foreach (Product product in results) { Console.WriteLine("{0}, {1}", product.ProductID, product.ProductName); } } This may be not straight forward enough. So here a solution will implement fluent reflection with a ToDynamic() extension method: IEnumerable<Product> results = database.ToDynamic() // Starts fluent reflection. .Provider.Execute(query.Expression).ReturnValue; C# 4.0 dynamic In this kind of scenarios, it is easy to have dynamic in mind, which enables developer to write whatever code after a dot: using (NorthwindDataContext database = new NorthwindDataContext()) { // Constructs the query. IQueryable<Product> query = database.Products.Where(product => product.ProductID > 0) .OrderBy(product => product.ProductName) .Take(2); // database.Provider dynamic dynamicDatabase = database; dynamic results = dynamicDatabase.Provider.Execute(query).ReturnValue; } This throws a RuntimeBinderException at runtime: 'System.Data.Linq.DataContext.Provider' is inaccessible due to its protection level. Here dynamic is able find the specified member. So the next thing is just writing some custom code to access the found member. .NET 4.0 DynamicObject, and DynamicWrapper<T> Where to put the custom code for dynamic? The answer is DynamicObject’s derived class. I first heard of DynamicObject from Anders Hejlsberg's video in PDC2008. It is very powerful, providing useful virtual methods to be overridden, like: TryGetMember() TrySetMember() TryInvokeMember() etc.  (In 2008 they are called GetMember, SetMember, etc., with different signature.) For example, if dynamicDatabase is a DynamicObject, then the following code: dynamicDatabase.Provider will invoke dynamicDatabase.TryGetMember() to do the actual work, where custom code can be put into. Now create a type to inherit DynamicObject: public class DynamicWrapper<T> : DynamicObject { private readonly bool _isValueType; private readonly Type _type; private T _value; // Not readonly, for value type scenarios. public DynamicWrapper(ref T value) // Uses ref in case of value type. { if (value == null) { throw new ArgumentNullException("value"); } this._value = value; this._type = value.GetType(); this._isValueType = this._type.IsValueType; } public override bool TryGetMember(GetMemberBinder binder, out object result) { // Searches in current type's public and non-public properties. PropertyInfo property = this._type.GetTypeProperty(binder.Name); if (property != null) { result = property.GetValue(this._value, null).ToDynamic(); return true; } // Searches in explicitly implemented properties for interface. MethodInfo method = this._type.GetInterfaceMethod(string.Concat("get_", binder.Name), null); if (method != null) { result = method.Invoke(this._value, null).ToDynamic(); return true; } // Searches in current type's public and non-public fields. FieldInfo field = this._type.GetTypeField(binder.Name); if (field != null) { result = field.GetValue(this._value).ToDynamic(); return true; } // Searches in base type's public and non-public properties. property = this._type.GetBaseProperty(binder.Name); if (property != null) { result = property.GetValue(this._value, null).ToDynamic(); return true; } // Searches in base type's public and non-public fields. field = this._type.GetBaseField(binder.Name); if (field != null) { result = field.GetValue(this._value).ToDynamic(); return true; } // The specified member is not found. result = null; return false; } // Other overridden methods are not listed. } In the above code, GetTypeProperty(), GetInterfaceMethod(), GetTypeField(), GetBaseProperty(), and GetBaseField() are extension methods for Type class. For example: internal static class TypeExtensions { internal static FieldInfo GetBaseField(this Type type, string name) { Type @base = type.BaseType; if (@base == null) { return null; } return @base.GetTypeField(name) ?? @base.GetBaseField(name); } internal static PropertyInfo GetBaseProperty(this Type type, string name) { Type @base = type.BaseType; if (@base == null) { return null; } return @base.GetTypeProperty(name) ?? @base.GetBaseProperty(name); } internal static MethodInfo GetInterfaceMethod(this Type type, string name, params object[] args) { return type.GetInterfaces().Select(type.GetInterfaceMap).SelectMany(mapping => mapping.TargetMethods) .FirstOrDefault( method => method.Name.Split('.').Last().Equals(name, StringComparison.Ordinal) && method.GetParameters().Count() == args.Length && method.GetParameters().Select( (parameter, index) => parameter.ParameterType.IsAssignableFrom(args[index].GetType())).Aggregate( true, (a, b) => a && b)); } internal static FieldInfo GetTypeField(this Type type, string name) { return type.GetFields( BindingFlags.GetField | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic).FirstOrDefault( field => field.Name.Equals(name, StringComparison.Ordinal)); } internal static PropertyInfo GetTypeProperty(this Type type, string name) { return type.GetProperties( BindingFlags.GetProperty | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic).FirstOrDefault( property => property.Name.Equals(name, StringComparison.Ordinal)); } // Other extension methods are not listed. } So now, when invoked, TryGetMember() searches the specified member and invoke it. The code can be written like this: dynamic dynamicDatabase = new DynamicWrapper<NorthwindDataContext>(ref database); dynamic dynamicReturnValue = dynamicDatabase.Provider.Execute(query.Expression).ReturnValue; This greatly simplified reflection. ToDynamic() and fluent reflection To make it even more straight forward, A ToDynamic() method is provided: public static class DynamicWrapperExtensions { public static dynamic ToDynamic<T>(this T value) { return new DynamicWrapper<T>(ref value); } } and a ToStatic() method is provided to unwrap the value: public class DynamicWrapper<T> : DynamicObject { public T ToStatic() { return this._value; } } In the above TryGetMember() method, please notice it does not output the member’s value, but output a wrapped member value (that is, memberValue.ToDynamic()). This is very important to make the reflection fluent. Now the code becomes: IEnumerable<Product> results = database.ToDynamic() // Here starts fluent reflection. .Provider.Execute(query.Expression).ReturnValue .ToStatic(); // Unwraps to get the static value. With the help of TryConvert(): public class DynamicWrapper<T> : DynamicObject { public override bool TryConvert(ConvertBinder binder, out object result) { result = this._value; return true; } } ToStatic() can be omitted: IEnumerable<Product> results = database.ToDynamic() .Provider.Execute(query.Expression).ReturnValue; // Automatically converts to expected static value. Take a look at the reflection code at the beginning of this post again. Now it is much much simplified! Special scenarios In 90% of the scenarios ToDynamic() is enough. But there are some special scenarios. Access static members Using extension method ToDynamic() for accessing static members does not make sense. Instead, DynamicWrapper<T> has a parameterless constructor to handle these scenarios: public class DynamicWrapper<T> : DynamicObject { public DynamicWrapper() // For static. { this._type = typeof(T); this._isValueType = this._type.IsValueType; } } The reflection code should be like this: dynamic wrapper = new DynamicWrapper<StaticClass>(); int value = wrapper._value; int result = wrapper.PrivateMethod(); So accessing static member is also simple, and fluent of course. Change instances of value types Value type is much more complex. The main problem is, value type is copied when passing to a method as a parameter. This is why ref keyword is used for the constructor. That is, if a value type instance is passed to DynamicWrapper<T>, the instance itself will be stored in this._value of DynamicWrapper<T>. Without the ref keyword, when this._value is changed, the value type instance itself does not change. Consider FieldInfo.SetValue(). In the value type scenarios, invoking FieldInfo.SetValue(this._value, value) does not change this._value, because it changes the copy of this._value. I searched the Web and found a solution for setting the value of field: internal static class FieldInfoExtensions { internal static void SetValue<T>(this FieldInfo field, ref T obj, object value) { if (typeof(T).IsValueType) { field.SetValueDirect(__makeref(obj), value); // For value type. } else { field.SetValue(obj, value); // For reference type. } } } Here __makeref is a undocumented keyword of C#. But method invocation has problem. This is the source code of TryInvokeMember(): public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { if (binder == null) { throw new ArgumentNullException("binder"); } MethodInfo method = this._type.GetTypeMethod(binder.Name, args) ?? this._type.GetInterfaceMethod(binder.Name, args) ?? this._type.GetBaseMethod(binder.Name, args); if (method != null) { // Oops! // If the returnValue is a struct, it is copied to heap. object resultValue = method.Invoke(this._value, args); // And result is a wrapper of that copied struct. result = new DynamicWrapper<object>(ref resultValue); return true; } result = null; return false; } If the returned value is of value type, it will definitely copied, because MethodInfo.Invoke() does return object. If changing the value of the result, the copied struct is changed instead of the original struct. And so is the property and index accessing. They are both actually method invocation. For less confusion, setting property and index are not allowed on struct. Conclusions The DynamicWrapper<T> provides a simplified solution for reflection programming. It works for normal classes (reference types), accessing both instance and static members. In most of the scenarios, just remember to invoke ToDynamic() method, and access whatever you want: StaticType result = someValue.ToDynamic()._field.Method().Property[index]; In some special scenarios which requires changing the value of a struct (value type), this DynamicWrapper<T> does not work perfectly. Only changing struct’s field value is supported. The source code can be downloaded from here, including a few unit test code.

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  • Using static vs. member find method on a STL set?

    - by B Johnson
    I am using a set because, i want to use the quick look up property of a sorted container such as a set. I am wondering if I have to use the find member method to get the benefit of a sorted container, or can I also use the static find method in the STL algorithms? My hunch is that using the static version will use a linear search instead of a binary search like I want.

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  • Why attached property Set and Get static methods are not called in XAML?

    - by JD
    Hi, I have set break points on my attached properties SetXXX and GetXXX static methods. In Xaml, I have assigned values to the attached property. However, I was expecting the Set or Get static methods to be called but they are not. The attached property works as expected and if I call SetXXX and GetXXX methods in code, then it works are expected. Why are the methods not called when set from Xaml? JD.

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  • Is there any way static block is executed more than once? if so then how?

    - by learner
    My Understanding Static block is executed during class loading, If a class is already loaded then there is no way to load the class other than class reloading Doubt/Question 1) Is there any time JVM reloads the class? My Understanding In Class Loading JVM loads source of the Java file, so it can not keep all thousands files source is a memory, it should discard the rarely used code and reload again when it is necessary and during reload JVM is not initializing static variables and locks again(may be using some tracking mechanism) Doubt/Question 2) If my above understanding is incorrect then please correct me

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  • What does a static modifier on a constructor means?

    - by the_drow
    I saw this kind of code at work: class FooPlugin : IPlugin // IPlugin is a Microsoft CRM component, it has something special about it's execution { static FooPlugin() { SomeObject.StaticFunction(); // The guy who wrote it said it's meaningful to this question but he can't remember why. } } Any idea what does a static modifier on a constructor mean and why in this case it is required?

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  • SQL select statement from 2 tables

    - by Steven
    Hi, I have a small sql question. I have 2 tables Members and Managers Members has: memberID, Name, Address Managers has: memberID, EditRights, DeleteRights EditRights and DeleteRights are of type bit. Mangers have a relationship with Members, because they are members themselves. I want to select all members id's, name and adress and for the members that are managers show if they have editrights and/or deleterights. SO: Exmaple data Members: ID, Name, Address 1, tom, 2 flat 2, dan, 3 flat 3, ben, 4 flat 4, bob, 6 flat 5, sam, 9 flat Managers: ID, Editrights, deleterights 2, 0, 1 4, 1, 1 5, 0, 0 I would like to display a select like this: 1, tom, 2 flat, no rights 2, dan, 3 flat, Delete 3, ben, 4 flat, no rights 4, bob, 6 flat, Edit&Delete 5, sam, 9 flat, no rights Any help would be great

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  • Django many-to-many relationship to self with extra data, how do I select from a certain direction?

    - by Jake
    I have some hierarchical data where each Set can have many members and can belong to more than one Set(group) Here are the models: class Set(models.Model): ... groups = models.ManyToManyField('self', through='Membership', symmetrical=False) members = models.ManyToManyField('self', through='Membership', symmetrical=False) class Membership(models.Model): group = models.ForeignKey( Set, related_name='Members' ) member = models.ForeignKey( Set, related_name='Groups' ) order = models.IntegerField( default=-1 ) I want to know how to get all the members or all the groups for a Set instance. I think I can do it as follows, but it's not very logical, can anyone tell me what's going on and how I should be doing it? # This gives me a set of Sets # Which seems to be the groups this Set belongs to set_instance.set_set.all() # These give me a set of Memberships, not Sets set_instance.Members.all() set_instance.Groups.all() # These they both return a set of Sets # which seem to be the members of this one set_instance.members.all() set_instance.groups.all()

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  • Joining two select queries and ordering results

    - by user1
    Basically I'm just unsure as to why this query is failing to execute: (SELECT replies.reply_post, replies.reply_content, replies.reply_date AS d, members.username FROM (replies) AS a INNER JOIN members ON replies.reply_by = members.id) UNION (SELECT posts.post_id, posts.post_title, posts.post_date AS d, members.username FROM (posts) as b WHERE posts.post_set = 0 INNER JOIN members ON posts.post_by = members.id) ORDER BY d DESC LIMIT 5 I'm getting this error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'a INNER JOIN members ON replies.re' at line 2 All I'm trying to do is select the 5 most recent rows (dates) from these two tables. I've tried Join, union etc and I've seen numerous queries where people have put another query after the FROM statement and that just makes no logical sense to me as to how that works? Am I safe to say that you can join the same table from two different but joined queries? Or am I taking completely the wrong approach, because frankly I can't seem see how this query is failing despite reading the error message. (The two queries on there own work fine)

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  • Extended Logging with Caller Info Attributes

    - by João Angelo
    .NET 4.5 caller info attributes may be one of those features that do not get much airtime, but nonetheless are a great addition to the framework. These attributes will allow you to programmatically access information about the caller of a given method, more specifically, the code file full path, the member name of the caller and the line number at which the method was called. They are implemented by taking advantage of C# 4.0 optional parameters and are a compile time feature so as an added bonus the returned member name is not affected by obfuscation. The main usage scenario will be for tracing and debugging routines as will see right now. In this sample code I’ll be using NLog, but the example is also applicable to other logging frameworks like log4net. First an helper class, without any dependencies and that can be used anywhere to obtain caller information: using System; using System.IO; using System.Runtime.CompilerServices; public sealed class CallerInfo { private CallerInfo(string filePath, string memberName, int lineNumber) { this.FilePath = filePath; this.MemberName = memberName; this.LineNumber = lineNumber; } public static CallerInfo Create( [CallerFilePath] string filePath = "", [CallerMemberName] string memberName = "", [CallerLineNumber] int lineNumber = 0) { return new CallerInfo(filePath, memberName, lineNumber); } public string FilePath { get; private set; } public string FileName { get { return this.fileName ?? (this.fileName = Path.GetFileName(this.FilePath)); } } public string MemberName { get; private set; } public int LineNumber { get; private set; } public override string ToString() { return string.Concat(this.FilePath, "|", this.MemberName, "|", this.LineNumber); } private string fileName; } Then an extension class specific for NLog Logger: using System; using System.Runtime.CompilerServices; using NLog; public static class LoggerExtensions { public static void TraceMemberEntry( this Logger logger, [CallerFilePath] string filePath = "", [CallerMemberName] string memberName = "", [CallerLineNumber] int lineNumber = 0) { LogMemberEntry(logger, LogLevel.Trace, filePath, memberName, lineNumber); } public static void TraceMemberExit( this Logger logger, [CallerFilePath] string filePath = "", [CallerMemberName] string memberName = "", [CallerLineNumber] int lineNumber = 0) { LogMemberExit(logger, LogLevel.Trace, filePath, memberName, lineNumber); } public static void DebugMemberEntry( this Logger logger, [CallerFilePath] string filePath = "", [CallerMemberName] string memberName = "", [CallerLineNumber] int lineNumber = 0) { LogMemberEntry(logger, LogLevel.Debug, filePath, memberName, lineNumber); } public static void DebugMemberExit( this Logger logger, [CallerFilePath] string filePath = "", [CallerMemberName] string memberName = "", [CallerLineNumber] int lineNumber = 0) { LogMemberExit(logger, LogLevel.Debug, filePath, memberName, lineNumber); } public static void LogMemberEntry( this Logger logger, LogLevel logLevel, [CallerFilePath] string filePath = "", [CallerMemberName] string memberName = "", [CallerLineNumber] int lineNumber = 0) { const string MsgFormat = "Entering member {1} at line {2}"; InternalLog(logger, logLevel, MsgFormat, filePath, memberName, lineNumber); } public static void LogMemberExit( this Logger logger, LogLevel logLevel, [CallerFilePath] string filePath = "", [CallerMemberName] string memberName = "", [CallerLineNumber] int lineNumber = 0) { const string MsgFormat = "Exiting member {1} at line {2}"; InternalLog(logger, logLevel, MsgFormat, filePath, memberName, lineNumber); } private static void InternalLog( Logger logger, LogLevel logLevel, string format, string filePath, string memberName, int lineNumber) { if (logger == null) throw new ArgumentNullException("logger"); if (logLevel == null) throw new ArgumentNullException("logLevel"); logger.Log(logLevel, format, filePath, memberName, lineNumber); } } Finally an usage example: using NLog; internal static class Program { private static readonly Logger Logger = LogManager.GetCurrentClassLogger(); private static void Main(string[] args) { Logger.TraceMemberEntry(); // Compile time feature // Next three lines output the same except for line number Logger.Trace(CallerInfo.Create().ToString()); Logger.Trace(() => CallerInfo.Create().ToString()); Logger.Trace(delegate() { return CallerInfo.Create().ToString(); }); Logger.TraceMemberExit(); } } NOTE: Code for helper class and Logger extension also available here.

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  • Exception Handling Frequency/Log Detail

    - by Cyborgx37
    I am working on a fairly complex .NET application that interacts with another application. Many single-line statements are possible culprits for throwing an Exception and there is often nothing I can do to check the state before executing them to prevent these Exceptions. The question is, based on best practices and seasoned experience, how frequently should I lace my code with try/catch blocks? I've listed three examples below, but I'm open to any advice. I'm really hoping to get some pros/cons of various approaches. I can certainly come up with some of my own (greater log granularity for the O-C approach, better performance for the Monolithic approach), so I'm looking for experience over opinion. EDIT: I should add that this application is a batch program. The only "recovery" necessary in most cases is to log the error, clean up gracefully, and quit. So this could be seen to be as much a question of log granularity as exception handling. In my mind's eye I can imagine good reasons for both, so I'm looking for some general advice to help me find an appropriate balance. Monolitich Approach class Program{ public static void Main(){ try{ Step1(); Step2(); Step3(); } catch (Exception e) { Log(e); } finally { CleanUp(); } } public static void Step1(){ ExternalApp.Dangerous1(); ExternalApp.Dangerous2(); } public static void Step2(){ ExternalApp.Dangerous3(); ExternalApp.Dangerous4(); } public static void Step3(){ ExternalApp.Dangerous5(); ExternalApp.Dangerous6(); } } Delegated Approach class Program{ public static void Main(){ try{ Step1(); Step2(); Step3(); } finally { CleanUp(); } } public static void Step1(){ try{ ExternalApp.Dangerous1(); ExternalApp.Dangerous2(); } catch (Exception e) { Log(e); throw; } } public static void Step2(){ try{ ExternalApp.Dangerous3(); ExternalApp.Dangerous4(); } catch (Exception e) { Log(e); throw; } } public static void Step3(){ try{ ExternalApp.Dangerous5(); ExternalApp.Dangerous6(); } catch (Exception e) { Log(e); throw; } } } Obsessive-Compulsive Approach class Program{ public static void Main(){ try{ Step1(); Step2(); Step3(); } finally { CleanUp(); } } public static void Step1(){ try{ ExternalApp.Dangerous1(); } catch (Exception e) { Log(e); throw; } try{ ExternalApp.Dangerous2(); } catch (Exception e) { Log(e); throw; } } public static void Step2(){ try{ ExternalApp.Dangerous3(); } catch (Exception e) { Log(e); throw; } try{ ExternalApp.Dangerous4(); } catch (Exception e) { Log(e); throw; } } public static void Step3(){ try{ ExternalApp.Dangerous5(); } catch (Exception e) { Log(e); throw; } try{ ExternalApp.Dangerous6(); } catch (Exception e) { Log(e); throw; } } } Other approaches welcomed and encouraged. Above are examples only.

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  • How can I prevent static when PC is plugged into an amplified speaker system?

    - by Kyle
    I've plugged a computer into an amp, using a 1/8 inch male extension cord, into a female adapter, that adapts into a male microphone 1/4 end. That being said, the amp sits at about half volume all the time because there are other things that play on it. (This issue is not flexible, nor is changing the amp) The problem is that now, even when I mute out the computer, you hear some static in the background. I was wondering some about some solutions (preferably multiple).

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  • Log Blog

    - by PointsToShare
    © 2011 By: Dov Trietsch. All rights reserved Logging – A log blog In a another blog (Missing Fields and Defaults) I spoke about not doing a blog about log files, but then I looked at it again and realized that this is a nice opportunity to show a simple yet powerful tool and also deal with static variables and functions in C#. My log had to be able to answer a few simple logging rules:   To log or not to log? That is the question – Always log! That is the answer  Do we share a log? Even when a file is opened with a minimal lock, it does not share well and performance greatly suffers. So sharing a log is not a good idea. Also, when sharing, it is harder to find your particular entries and you have to establish rules about retention. My recommendation – Do Not Share!  How verbose? Your log can be very verbose – a good thing when testing, very terse – a good thing in day-to-day runs, or somewhere in between. You must be the judge. In my Blog, I elect to always report a run with start and end times, and always report errors. I normally use 5 levels of logging: 4 – write all, 3 – write more, 2 – write some, 1 – write errors and timing, 0 – write none. The code sample below is more general than that. It uses the config file to set the max log level and each call to the log assigns a level to the call itself. If the level is above the .config highest level, the line will not be written. Programmers decide which log belongs to which level and thus we can set the .config differently for production and testing.  Where do I keep the log? If your career is important to you, discuss this with the boss and with the system admin. We keep logs in the L: drive of our server and make sure that we have a directory for each app that needs a log. When adding a new app, add a new directory. The default location for the log is also found in the .config file Print One or Many? There are two options here:   1.     Print many, Open but once once – you start the stream and close it only when the program ends. This is what you can do when you perform in “batch” mode like in a console app or a stsadm extension.The advantage to this is that starting a closing a stream is expensive and time consuming and because we use a unique file, keeping it open for a long time does not cause contention problems. 2.     Print one entry at a time or Open many – every time you write a line, you start the stream, write to it and close it. This work for event receivers, feature receivers, and web parts. Here scalability requires us to create objects on the fly and get rid of them as soon as possible.  A default value of the onceOrMany resides in the .config.  All of the above applies to any windows or web application, not just SharePoint.  So as usual, here is a routine that does it all, and a few simple functions that call it for a variety of purposes.   So without further ado, here is app.config  <?xml version="1.0" encoding="utf-8" ?> <configuration>     <configSections>         <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=2.0.0.0, Culture=neutral, ublicKeyToken=b77a5c561934e089" >         <section name="statics.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />         </sectionGroup>     </configSections>     <applicationSettings>         <statics.Properties.Settings>             <setting name="oneOrMany" serializeAs="String">                 <value>False</value>             </setting>             <setting name="logURI" serializeAs="String">                 <value>C:\staticLog.txt</value>             </setting>             <setting name="highestLevel" serializeAs="String">                 <value>2</value>             </setting>         </statics.Properties.Settings>     </applicationSettings> </configuration>   And now the code:  In order to persist the variables between calls and also to be able to persist (or not to persist) the log file itself, I created an EventLog class with static variables and functions. Static functions do not need an instance of the class in order to work. If you ever wondered why our Main function is static, the answer is that something needs to run before instantiation so that other objects may be instantiated, and this is what the “static” Main does. The various logging functions and variables are created as static because they do not need instantiation and as a fringe benefit they remain un-destroyed between calls. The Main function here is just used for testing. Note that it does not instantiate anything, just uses the log functions. This is possible because the functions are static. Also note that the function calls are of the form: Class.Function.  using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.IO; namespace statics {       class Program     {         static void Main(string[] args)         {             //write a single line             EventLog.LogEvents("ha ha", 3, "C:\\hahafile.txt", 4, true, false);             //this single line will not be written because the msgLevel is too high             EventLog.LogEvents("baba", 3, "C:\\babafile.txt", 2, true, false);             //The next 4 lines will be written in succession - no closing             EventLog.LogLine("blah blah", 1);             EventLog.LogLine("da da", 1);             EventLog.LogLine("ma ma", 1);             EventLog.LogLine("lah lah", 1);             EventLog.CloseLog(); // log will close             //now with specific functions             EventLog.LogSingleLine("one line", 1);             //this is just a test, the log is already closed             EventLog.CloseLog();         }     }     public class EventLog     {         public static string logURI = Properties.Settings.Default.logURI;         public static bool isOneLine = Properties.Settings.Default.oneOrMany;         public static bool isOpen = false;         public static int highestLevel = Properties.Settings.Default.highestLevel;         public static StreamWriter sw;         /// <summary>         /// the program will "print" the msg into the log         /// unless msgLevel is > msgLimit         /// onceOrMany is true when once - the program will open the log         /// print the msg and close the log. False when many the program will         /// keep the log open until close = true         /// normally all the arguments will come from the app.config         /// called by many overloads of logLine         /// </summary>         /// <param name="msg"></param>         /// <param name="msgLevel"></param>         /// <param name="logFileName"></param>         /// <param name="msgLimit"></param>         /// <param name="onceOrMany"></param>         /// <param name="close"></param>         public static void LogEvents(string msg, int msgLevel, string logFileName, int msgLimit, bool oneOrMany, bool close)         {             //to print or not to print             if (msgLevel <= msgLimit)             {                 //open the file. from the argument (logFileName) or from the config (logURI)                 if (!isOpen)                 {                     string logFile = logFileName;                     if (logFileName == "")                     {                         logFile = logURI;                     }                     sw = new StreamWriter(logFile, true);                     sw.WriteLine("Started At: " + DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"));                     isOpen = true;                 }                 //print                 sw.WriteLine(msg);             }             //close when instructed             if (close || oneOrMany)             {                 if (isOpen)                 {                     sw.WriteLine("Ended At: " + DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"));                     sw.Close();                     isOpen = false;                 }             }         }           /// <summary>         /// The simplest, just msg and level         /// </summary>         /// <param name="msg"></param>         /// <param name="msgLevel"></param>         public static void LogLine(string msg, int msgLevel)         {             //use the given msg and msgLevel and all others are defaults             LogEvents(msg, msgLevel, "", highestLevel, isOneLine, false);         }                 /// <summary>         /// one line at a time - open print close         /// </summary>         /// <param name="msg"></param>         /// <param name="msgLevel"></param>         public static void LogSingleLine(string msg, int msgLevel)         {             LogEvents(msg, msgLevel, "", highestLevel, true, true);         }           /// <summary>         /// used to close. high level, low limit, once and close are set         /// </summary>         /// <param name="close"></param>         public static void CloseLog()         {             LogEvents("", 15, "", 1, true, true);         }           }     }   }   That’s all folks!

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  • Help needed setting up nginx to serve static files.

    - by Catalina
    Hi Guys, I'm trying to setup nginx to serve static files. Basically all I need is to have http://mydomain.com/site_media/ point to /var/django/myproject/site_media. I have tried so many configurations and when I test it I always get a 404 error for static files. Can anyone please tell me what I'm doing wrong or how I should be setting this up? This is my current nginx configuration file. user www-data; worker_processes 1; #error_log /usr/local/nginx/logs/error.log; #pid /usr/local/nginx/logs/nginx.pid; events { worker_connections 1024; use epoll; } http { # Enumerate all the Tornado servers here upstream frontends { server 127.0.0.1:8000; server 127.0.0.1:8001; server 127.0.0.1:8002; server 127.0.0.1:8003; } include mime.types; default_type application/octet-stream; #access_log /usr/local/nginx/logs/access.log; keepalive_timeout 65; proxy_read_timeout 200; sendfile on; tcp_nopush on; tcp_nodelay on; gzip on; gzip_min_length 1000; gzip_proxied any; gzip_types text/plain text/html text/css text/xml application/x-javascript application/xml application/atom+xml text/javascript; proxy_next_upstream error; server { listen 80; # Allow file uploads client_max_body_size 50M; location ^~ /site_media/ { root /var/django/myproject/site_media; if ($query_string) { expires max; } } location = /favicon.ico { rewrite (.*) /site_media/favicon.ico; } location = /robots.txt { rewrite (.*) /site_media/robots.txt; } location / { proxy_pass_header Server; proxy_set_header Host $http_host; proxy_redirect off; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Scheme $scheme; proxy_pass http://frontends; } } #include /usr/local/nginx/sites-enabled/*; } Thanks, Cata

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