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• Does it ever make sense to make a fundamental (non-pointer) parameter const?

  - by Scott Smith

  I recently had an exchange with another C++ developer about the following use of const: void Foo(const int bar); He felt that using const in this way was good practice. I argued that it does nothing for the caller of the function (since a copy of the argument was going to be passed, there is no additional guarantee of safety with regard to overwrite). In addition, doing this prevents the implementer of Foo from modifying their private copy of the argument. So, it both mandates and advertises an implementation detail. Not the end of the world, but certainly not something to be recommended as good practice. I'm curious as to what others think on this issue. Edit: OK, I didn't realize that const-ness of the arguments didn't factor into the signature of the function. So, it is possible to mark the arguments as const in the implementation (.cpp), and not in the header (.h) - and the compiler is fine with that. That being the case, I guess the policy should be the same for making local variables const. One could make the argument that having different looking signatures in the header and source file would confuse others (as it would have confused me). While I try to follow the Principle of Least Astonishment with whatever I write, I guess it's reasonable to expect developers to recognize this as legal and useful.

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• Extending the method pool of a concrete class which is derived by an interface

  - by CelGene

  Hello, I had created an interface to abstract a part of the source for a later extension. But what if I want to extend the derived classes with some special methods? So I have the interface here: class virtualFoo { public: virtual ~virtualFoo() { } virtual void create() = 0; virtual void initialize() = 0; }; and one derived class with an extra method: class concreteFoo : public virtualFoo { public: concreteFoo() { } ~concreteFoo() { } virtual void create() { } virtual void initialize() { } void ownMethod() { } }; So I try to create an Instance of concreteFoo and try to call ownMethod like this: void main() { virtualFoo* ptr = new concreteFoo(); concreteFoo* ptr2 = dynamic_cast(ptr); if(NULL != ptr2) ptr2->ownMethod(); } It works but is not really the elegant way. If I would try to use ptr-ownMethod(); directly the compiler complains that this method is not part of virtualFoo. Is there a chance to do this without using dynamic_cast? Thanks in advance!

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• User defined literal arguments are not constexpr?

  - by Pubby

  I'm testing out user defined literals. I want to make _fac return the factorial of the number. Having it call a constexpr function works, however it doesn't let me do it with templates as the compiler complains that the arguments are not and cannot be constexpr. I'm confused by this - aren't literals constant expressions? The 5 in 5_fac is always a literal that can be evaluated during compile time, so why can't I use it as such? First method: constexpr int factorial_function(int x) { return (x > 0) ? x * factorial_function(x - 1) : 1; } constexpr int operator "" _fac(unsigned long long x) { return factorial_function(x); // this works } Second method: template <int N> struct factorial { static const unsigned int value = N * factorial<N - 1>::value; }; template <> struct factorial<0> { static const unsigned int value = 1; }; constexpr int operator "" _fac(unsigned long long x) { return factorial_template<x>::value; // doesn't work - x is not a constexpr }

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• How do I implement configurations and settings?

  - by Malvolio

  I'm writing a system that is deployed in several places and each site needs its own configurations and settings. A "configuration" is a named value that is necessary to a particular site (e.g., the database URL, S3 bucket name); every configuration is necessary, there is not usually a default, and it's typically string-valued. A setting is a named value but it just tweaks the behavior of the system; it's often numeric or Boolean, and there's usually some default. So far, I've been using property files or thing like them, but it's a terrible solution. Several times, a developer has added a requirement for a configuration but not added the value to file for the live configuration, so the new release passed all the tests, then failed when released to live. Better, of course, for every file to be compiled — so if there's a missing configuration, or one of the wrong type, it won't get past the compiler — and inject the site-specific class into the build for each site. As a bones, a Scala file can easy model more complex values, especially lists, but also maps and tuples. The downside is, the files are sometimes maintained by people who aren't developers, so it has to be pretty self-explanatory, which was the advantage of property files. (Someone explain XML configurations to me: all the complexity of a compilable file but the run-time risk of a property file.) What I'm looking for is an easy pattern for defining a group required names and allowable values. Any suggestions?

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• Native Endians and Auto Conversion

  - by KnickerKicker

  so the following converts big endians to little ones uint32_t ntoh32(uint32_t v) { return (v << 24) | ((v & 0x0000ff00) << 8) | ((v & 0x00ff0000) >> 8) | (v >> 24); } works. like a charm. I read 4 bytes from a big endian file into char v[4] and pass it into the above function as ntoh32 (* reinterpret_cast<uint32_t *> (v)) that doesn't work - because my compiler (VS 2005) automatically converts the big endian char[4] into a little endian uint32_t when I do the cast. AFAIK, this automatic conversion will not be portable, so I use uint32_t ntoh_4b(char v[]) { uint32_t a = 0; a |= (unsigned char)v[0]; a <<= 8; a |= (unsigned char)v[1]; a <<= 8; a |= (unsigned char)v[2]; a <<= 8; a |= (unsigned char)v[3]; return a; } yes the (unsigned char) is necessary. yes it is dog slow. there must be a better way. anyone ?

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• Resources and techniques/methods for SCJP preparation ?

  - by BenoitParis

  I am passing the SCJP 6 exam in a month. I have the "SCJP Sun Certified Programmer for Java 6 Exam 310-065" book. It seems great for the exam. But I want your advice on this. Getting the closest possible to 100% would be great. I have found a site that answered some of the questions you ask yourself when you go trough the book. Here is it : http://www.janeg.ca/java2.html As you can see it was written for Java 2 :/ I have written another specific question here on StackOverflow about the usefulness of JVM specification and Java compiler code for the SCJP. Will Update the results here. Here it is. Please share the resources you used in preparing the exam. Please also specify any resources that you think might help. Any type of resource is welcome: books, code, specs, sites, wikies, papers, online tests, grandmas... Please also share on any method/technique that helped you prepare the exam. Please also comment on the return you got from the resource and the method (for the learning process and for points in the exam) I'll begin: Book : "SCJP Sun Certified Programmer for Java 6 Exam 310-065". Seems like the official book for the preparation. Technique : Writing code in a text editor and compiling it with javac to test a question. NO IDEs! It helps you get a a straight answer to a question you have. It helps you pay attention to every word in the code (and this is very important in the SCJP) EDIT: Added dimension: Are there good, up-to-date online tests?

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• Can C++ do something like an ML case expression?

  - by Nathan Andrew Mullenax

  So, I've run into this sort of thing a few times in C++ where I'd really like to write something like case (a,b,c,d) of (true, true, _, _ ) => expr | (false, true, _, false) => expr | ... But in C++, I invariably end up with something like this: bool c11 = color1.count(e.first)>0; bool c21 = color2.count(e.first)>0; bool c12 = color1.count(e.second)>0; bool c22 = color2.count(e.second)>0; // no vertex in this edge is colored // requeue if( !(c11||c21||c12||c22) ) { edges.push(e); } // endpoints already same color // failure condition else if( (c11&&c12)||(c21&&c22) ) { results.push_back("NOT BICOLORABLE."); return true; } // nothing to do: nodes are already // colored and different from one another else if( (c11&&c22)||(c21&&c12) ) { } // first is c1, second is not set else if( c11 && !(c12||c22) ) { color2.insert( e.second ); } // first is c2, second is not set else if( c21 && !(c12||c22) ) { color1.insert( e.second ); } // first is not set, second is c1 else if( !(c11||c21) && c12 ) { color2.insert( e.first ); } // first is not set, second is c2 else if( !(c11||c21) && c22 ) { color1.insert( e.first ); } else { std::cout << "Something went wrong.\n"; } I'm wondering if there's any way to clean all of those if's and else's up, as it seems especially error prone. It would be even better if it were possible to get the compiler complain like SML does when a case expression (or statement in C++) isn't exhaustive. I realize this question is a bit vague. Maybe, in sum, how would one represent an exhaustive truth table with an arbitrary number of variables in C++ succinctly? Thanks in advance.

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• Delphi: How to avoid EIntOverflow underflow when subtracting?

  - by Ian Boyd

  Microsoft already says, in the documentation for GetTickCount, that you could never compare tick counts to check if an interval has passed. e.g.: Incorrect (pseudo-code): DWORD endTime = GetTickCount + 10000; //10 s from now ... if (GetTickCount > endTime) break; The above code is bad because it is suceptable to rollover of the tick counter. For example, assume that the clock is near the end of it's range: endTime = 0xfffffe00 + 10000 = 0x00002510; //9,488 decimal Then you perform your check: if (GetTickCount > endTime) Which is satisfied immediatly, since GetTickCount is larger than endTime: if (0xfffffe01 > 0x00002510) The solution Instead you should always subtract the two time intervals: DWORD startTime = GetTickCount; ... if (GetTickCount - startTime) > 10000 //if it's been 10 seconds break; Looking at the same math: if (GetTickCount - startTime) > 10000 if (0xfffffe01 - 0xfffffe00) > 10000 if (1 > 10000) Which is all well and good in C/C++, where the compiler behaves a certain way. But what about Delphi? But when i perform the same math in Delphi, with overflow checking on ({Q+}, {$OVERFLOWCHECKS ON}), the subtraction of the two tick counts generates an EIntOverflow exception when the TickCount rolls over: if (0x00000100 - 0xffffff00) > 10000 0x00000100 - 0xffffff00 = 0x00000200 What is the intended solution for this problem? Edit: i've tried to temporarily turn off OVERFLOWCHECKS: {$OVERFLOWCHECKS OFF}] delta = GetTickCount - startTime; {$OVERFLOWCHECKS ON} But the subtraction still throws an EIntOverflow exception. Is there a better solution, involving casts and larger intermediate variable types?

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• Foreign key relationships in Entity Framework

  - by Anders Svensson

  I'm trying to add an object created from Entity Data Model classes. I have a table called Users, which has turned into a User EDM class. And I also have a table Pages, which has become a Page EDM class. These tables have a foreign key relationship, so that each page is associated with many users. Now I want to be able to add a page, but I can't get how to do it. I get a nullreference exception on Users below. I'm still rather confused by all this, so I'm sure it's a simple error, but I just can't see how to do it. Also, by the way, the compiler requires that I set PageID in the object initializer, even though this field is set to be an automatic id in the table. Am I doing it right just setting it to 0, expecting it to be updated automatically in the table when saved, or how should I do that? Any help appreciated! The method in question: private Page GetPage(User currentUser) { string url = _request.ServerVariables["url"].ToLower(); var userPages = from p in _context.PageSet where p.Users.UserID == currentUser.UserID select p; var existingPage = userPages.FirstOrDefault(e => e.Url == url); //Could be combined with above, but hard to read? if (existingPage != null) return existingPage; Page page = new Page() { Count = 0, Url = _request.ServerVariables["url"].ToLower(), PageID = 0, //Only initial value, changed later? }; _context.AddToPageSet(page); page.Users.UserID = currentUser.UserID; //Here's the problem... return page; }

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• How are two-dimensional arrays formatted in memory?

  - by Chris Cooper

  In C, I know I can dynamically allocate a two-dimensional array on the heap using the following code: int** someNumbers = malloc(arrayRows*sizeof(int*)); for (i = 0; i < arrayRows; i++) { someNumbers[i] = malloc(arrayColumns*sizeof(int)); } Clearly, this actually creates a one-dimensional array of pointers to a bunch of separate one-dimensional arrays of integers, and "The System" can figure you what I mean when I ask for: someNumbers[4][2]; But when I statically declare a 2D array, as in the following line...: int someNumbers[ARRAY_ROWS][ARRAY_COLUMNS]; ...does a similar structure get created on the stack, or is it of another form completely? (i.e. is it a 1D array of pointers? If not, what is it, and how do references to it get figured out?) Also, when I said, "The System," what is actually responsible for figuring that out? The kernel? Or does the C compiler sort it out while compiling?

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• Using child visitor in C#

  - by Thomas Matthews

  I am setting up a testing component and trying to keep it generic. I want to use a generic Visitor class, but not sure about using descendant classes. Example: public interface Interface_Test_Case { void execute(); void accept(Interface_Test_Visitor v); } public interface Interface_Test_Visitor { void visit(Interface_Test_Case tc); } public interface Interface_Read_Test_Case : Interface_Test_Case { uint read_value(); } public class USB_Read_Test : Interface_Read_Test_Case { void execute() { Console.WriteLine("Executing USB Read Test Case."); } void accept(Interface_Test_Visitor v) { Console.WriteLine("Accepting visitor."); } uint read_value() { Console.WriteLine("Reading value from USB"); return 0; } } public class USB_Read_Visitor : Interface_Test_Visitor { void visit(Interface_Test_Case tc) { Console.WriteLine("Not supported Test Case."); } void visit(Interface_Read_Test_Case rtc) { Console.WriteLine("Not supported Read Test Case."); } void visit(USB_Read_Test urt) { Console.WriteLine("Yay, visiting USB Read Test case."); } } // Code fragment USB_Read_Test test_case; USB_Read_Visitor visitor; test_case.accept(visitor); What are the rules the C# compiler uses to determine which of the methods in USB_Read_Visitor will be executed by the code fragment? I'm trying to factor out dependencies of my testing component. Unfortunately, my current Visitor class contains visit methods for classes not related to the testing component. Am I trying to achieve the impossible?

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• C++ Implicit Conversion Operators

  - by Imbue

  I'm trying to find a nice inheritance solution in C++. I have a Rectangle class and a Square class. The Square class can't publicly inherit from Rectangle, because it cannot completely fulfill the rectangle's requirements. For example, a Rectangle can have it's width and height each set separately, and this of course is impossible with a Square. So, my dilemma. Square obviously will share a lot of code with Rectangle; they are quite similar. For examlpe, if I have a function like: bool IsPointInRectangle(const Rectangle& rect); it should work for a square too. In fact, I have a ton of such functions. So in making my Square class, I figured I would use private inheritance with a publicly accessible Rectangle conversion operator. So my square class looks like: class Square : private Rectangle { public: operator const Rectangle&() const; }; However, when I try to pass a Square to the IsPointInRectangle function, my compiler just complains that "Rectangle is an inaccessible base" in that context. I expect it to notice the Rectangle operator and use that instead. Is what I'm trying to do even possible? If this can't work I'm probably going to refactor part of Rectangle into MutableRectangle class. Thanks.

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• How do I access Dictionary items?

  - by salvationishere

  I am developing a C# VS2008 / SQL Server website app and am new to the Dictionary class. Can you please advise on best method of accomplishing this? Here is a code snippet: SqlConnection conn2 = new SqlConnection(connString); SqlCommand cmd = conn2.CreateCommand(); cmd.CommandText = "dbo.AppendDataCT"; cmd.CommandType = CommandType.StoredProcedure; cmd.Connection = conn2; SqlParameter p1, p2, p3; foreach (string s in dt.Rows[1].ItemArray) { DataRow dr = dt.Rows[1]; // second row p1 = cmd.Parameters.AddWithValue((string)dic[0], (string)dr[0]); p1.SqlDbType = SqlDbType.VarChar; p2 = cmd.Parameters.AddWithValue((string)dic[1], (string)dr[1]); p2.SqlDbType = SqlDbType.VarChar; p3 = cmd.Parameters.AddWithValue((string)dic[2], (string)dr[2]); p3.SqlDbType = SqlDbType.VarChar; } but this is giving me compiler error: The best overloaded method match for 'System.Collections.Generic.Dictionary<string,string>.this[string]' has some invalid arguments I just want to access each value from "dic" and load into these SQL parameters. How do I do this? Do I have to enter the key? The keys are named "col1", "col2", etc., so not the most user-friendly. Any other tips? Thanks!

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• Alternatives to static methods on interfaces for enforcing consistency

  - by jayshao

  In Java, I'd like to be able to define marker interfaces, that forced implementations to provide static methods. For example, for simple text-serialization/deserialization I'd like to be able to define an interface that looked something like this: public interface TextTransformable<T>{ public static T fromText(String text); public String toText(); Since interfaces in Java can't contain static methods though (as noted in a number of other posts/threads: here, here, and here this code doesn't work. What I'm looking for however is some reasonable paradigm to express the same intent, namely symmetric methods, one of which is static, and enforced by the compiler. Right now the best we can come up with is some kind of static factory object or generic factory, neither of which is really satisfactory. Note: in our case our primary use-case is we have many, many "value-object" types - enums, or other objects that have a limited number of values, typically carry no state beyond their value, and which we parse/de-parse thousands of time a second, so actually do care about reusing instances (like Float, Integer, etc.) and its impact on memory consumption/g.c. Any thoughts?

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• ojspc always returns 0 on errors

  - by Matt McCormick

  In my Ant build.xml file, I am trying to compile JSPs using ojspc. The files are being compiled, however, the build process is still running to completion when the JSP compilation has errors. This is part of my build.xml: <java fork="true" jar="${env.ORACLE_HOME}\j2ee\home\ojspc.jar" resultproperty="result"> <jvmarg value="-Djava.compiler=NONE"/> <arg value="-extend"/> <arg value="com.orionserver.http.OrionHttpJspPage"/> <arg value="-batchMask"/> <arg value="*.jsp"/> <arg value="${target-directory}/build/target/ear/${module-dir-name}-jsp.war"/> </java> <echo level="info">Result Property: ${result}</echo> I have tried setting the property failonerror="true" but that does not change anything. I receive the following output: [java] Detected archive, now processing contents of ../build/target/ear/web-module-jsp.war... [java] Setting up temp area... [java] Expanding archive in temp area... [java] C:\DOCUME~1\MMCCOR~1\LOCALS~1\Temp\tmp12940\_web_2d_inf\_jsp\_password.java:60: cannot resolve symbol [java] symbol : variable reqvst [java] location: class _web_2d_inf._jsp._password [java] out.print(reqvst.getAttribute("test")); [java] ^ [java] 1 error [java] Creating D:\eclipse-workspace\jdw\build\..\build\target\ear\web-module-jsp.war ... [java] Removing temp area... [echo] Result Property: 0 ...(more commands) BUILD SUCCESSFUL In the password.jsp file, I intentionally introduced an error to test. How can I get the build to fail on an error? At the Ant Java page, I am confused by: By default the return code of a is ignored. Alternatively, you can set resultproperty to the name of a property and have it assigned to the result code (barring immutability, of course). When you set failonerror="true", the only possible value for resultproperty is 0. Any non-zero response is treated as an error and would mean the build exits.

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• Putting all methods in class definition

  - by Amnon

  When I use the pimpl idiom, is it a good idea to put all the methods definitions inside the class definition? For example: // in A.h class A { class impl; boost::scoped_ptr<impl> pimpl; public: A(); int foo(); } // in A.cpp class A::impl { // method defined in class int foo() { return 42; } // as opposed to only declaring the method, and defining elsewhere: float bar(); }; A::A() : pimpl(new impl) { } int A::foo() { return pimpl->foo(); } As far as I know, the only problems with putting a method definition inside a class definition is that (1) the implementation is visible in files that include the class definition, and (2) the compiler may make the method inline. These are not problems in this case since the class is defined in a private file, and inlining has no effect since the methods are called in only one place. The advantage of putting the definition inside the class is that you don't have to repeat the method signature. So, is this OK? Are there any other issues to be aware of?

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• C++ Constructor initialization list strangeness

  - by Andy

  I have always been a good boy when writing my classes, prefixing all member variables with m_: class Test { int m_int1; int m_int2; public: Test(int int1, int int2) : m_int1(int int1), m_int2(int int2) {} }; void main() { Test t(10, 20); // Just an example } However, recently I forgot to do that and ended up writing: class Test { int int1; int int2; public: // Very questionable, but of course I meant to assign ::int1 to this->int1! Test(int int1, int int2) : int1(int1), int2(int2) {} }; Believe it or not, the code compiled with no errors/warnings and the assignments took place correctly! It was only when doing the final check before checking in my code when I realised what I had done. My question is: why did my code compile? Is something like that allowed in the C++ standard, or is it simply a case of the compiler being clever? In case you were wondering, I was using Visual Studio 2008 Thank you.

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• how to filter files from the root "classes" and "test-classes" folders in Eclipse?

  - by Kidburla

  I am using ClearCase in my application which generates a whole load of ".copyarea.db" files (one in every folder). These cause conflicts when publishing to Tomcat as Eclipse will bundle the "classes" and "test-classes" folders into one JAR (not sure why it does this - as there is no need to have test classes available on the application server). Any folders with the same names will have a separate .copyarea.db in the classes and test-classes branches. I managed to get around this problem in general by adding ".copyarea.db" to the Filtered resources on the Java->Compiler->Building->Output Folder preference page. This stops the file appearing in source output (package/class folders), the vast majority of cases. However there remains the problem of the root folder, i.e. "target/classes/.copyarea.db" and "target/test-classes/.copyarea.db". These files are not filtered as they are not part of the compile task. Just deleting the files manually doesn't help either, as Eclipse expects to find them and doesn't. How can I exclude these ".copyarea.db" files from the root "classes" and "test-classes" folders?

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• Trying to make a plugin system in C++

  - by Pirate for Profit

  I'm making a task-based program that needs to have plugins. Tasks need to have properties which can be easily edited, I think this can be done with Qt's Meta-Object Compiler reflection capabilities (I could be wrong, but I should be able to stick this in a QtPropertyBrowser?) So here's the base: class Task : public QObject { Q_OBJECT public: explicit Task(QObject *parent = 0) : QObject(parent){} virtual void run() = 0; signals: void taskFinished(bool success = true); } Then a plugin might have this task: class PrinterTask : public Task { Q_OBJECT public: explicit PrinterTask(QObject *parent = 0) : Task(parent) {} void run() { Printer::getInstance()->Print(this->getData()); // fictional emit taskFinished(true); } inline const QString &getData() const; inline void setData(QString data); Q_PROPERTY(QString data READ getData WRITE setData) // for reflection } In a nutshell, here's what I want to do: // load plugin // find all the Tasks interface implementations in it // have user able to choose a Task and edit its specific Q_PROPERTY's // run the TASK It's important that one .dll has multiple tasks, because I want them to be associated by their module. For instance, "FileTasks.dll" could have tasks for deleting files, making files, etc. The only problem with Qt's plugin setup is I want to store X amount of Tasks in one .dll module. As far as I can tell, you can only load one interface per plugin (I could be wrong?). If so, the only possible way to do accomplish what I want is to create a FactoryInterface with string based keys which return the objects (as in Qt's Plug-And-Paint example), which is a terrible boilerplate that I would like to avoid. Anyone know a cleaner C++ plugin architecture than Qt's to do what I want? Also, am I safely assuming Qt's reflection capabilities will do what I want (i.e. able to edit an unknown dynamically loaded tasks' properties with the QtPropertyBrowser before dispatching)?

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• different thread accessing MemoryStream

  - by Wayne

  There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately. This code works purposes 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem is that the memory.Position property suddenly returns zero instead of the appropriate value. However, code was added that checks for the 0 and throws an exception which include log of the MemoryStream properties like Position and Length in a separate method. Those return the correct value. Further addition shows that when this rare condition occurs, the memory.Position only has zero inside this particular method. Okay. Obviously, this must be a threading issue. But this code is well locked. However, the nature of this software is that it's organized by "tasks" with a scheduler and so any one of several actual O/S thread may run this code at any give time--but never more than one at a time. So it's my guess that ordinarily it so happens that the same thread keeps getting used for this method and then on a rare occasion a different thread get used. Then due to compiler optimizations, the different thread never gets the correct value. It gets a "stale" value. Ordinarily in a situation like this I would apply a "volatile" keyword to the variable in question. But that (those) variables are inside the MemoryStream object. Does anyone have any other idea? Or does this mean we have to implement our own MemoryStream object? (Just like we end up having to do with practically every collection in .NET?) It's a shame to have such an awesome platform as .NET and have virtually the entire system useless as-is for seriously parallelized applications. If I'm wrong or you have other ideas, please advise. Sincerely, Wayne

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• Why do .NET developers offer 32-bit/64-bit versions of .NET assemblies?

  - by Tyler

  Evey now and then I see both x86 and x64 versions of a .NET assembly. Consider the following web part for SharePoint. Why wouldn't the developer just offer a single version and have let the JIT compiler sort out the rest? When I see these kinds offering is it just that the developer decided to create a native image using a tool like ngen in order to avoid a JIT? Someone please help me out here, I feel like I'm missing something of note. Updated From what I got below, both x86 and x64 builds are offered because one or more of the following reasons: The developer wanted to avoid JITing and created a native image of his code, targeting a given architecture using a tool like ngen.exe. The assembly contains platform specific COM calls and so it makes no point to build it as AnyCPU. In these cases builds that target different platforms may contain different code. The assembly may contain Win32 calls using pinvoke which won't get remapped by a JIT and so the build should target the platform it is bound to.

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• C#: Need one of my classes to trigger an event in another class to update a text box

  - by Matt

  Total n00b to C# and events although I have been programming for a while. I have a class containing a text box. This class creates an instance of a communication manager class that is receiving frames from the Serial Port. I have this all working fine. Every time a frame is received and its data extracted, I want a method to run in my class with the text box in order to append this frame data to the text box. So, without posting all of my code I have my form class... public partial class Form1 : Form { CommManager comm; public Form1() { InitializeComponent(); comm = new CommManager(); } private void updateTextBox() { //get new values and update textbox } . . . and I have my CommManager class class CommManager { //here we manage the comms, recieve the data and parse the frame } SO... essentially, when I parse that frame, I need the updateTextBox method from the form class to run. I'm guessing this is possible with events but I can't seem to get it to work. I tried adding an event handler in the form class after creating the instance of CommManager as below... comm = new CommManager(); comm.framePopulated += new EventHandler(updateTextBox); ...but I must be doing this wrong as the compiler doesn't like it... Any ideas?!

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• display multiple errors via bool flag c++

  - by igor

  Been a long night, but stuck on this and now am getting "segmentation fault" in my compiler.. Basically I'm trying to display all the errors (the cout) needed. If there is more than one error, I am to display all of them. bool validMove(const Square board[BOARD_SIZE][BOARD_SIZE], int x, int y, int value) { int index; bool moveError = true; const int row_conflict(0), column_conflict(1), grid_conflict(2); int v_subgrid=x/3; int h_subgrid=y/3; getCoords(x,y); for(index=0;index<9;index++) if(board[x][index].number==value){ cout<<"That value is in conflict in this row\n"; moveError=false; } for(index=0;index<9;index++) if(board[index][y].number==value){ cout<<"That value is in conflict in this column\n"; moveError=false; } for(int i=v_subgrid*3;i<(v_subgrid*3 +3);i++){ for(int j=h_subgrid*3;j<(h_subgrid*3+3);j++){ if(board[i][j].number==value){ cout<<"That value is in conflict in this subgrid\n"; moveError=false; } } } return true; }

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• Problems with variadic function

  - by morpheous

  I have the following function from some legacy code that I am maintaining. long getMaxStart(long start, long count, const myStruct *s1, ...) { long i1, maxstart; myStruct *s2; va_list marker; maxstart = start; /*BUGFIX: 003 */ /*(va_start(marker, count);*/ va_start(marker, s1); for (i1 = 1; i1 <= count; i1++) { s2 = va_arg(marker, myStruct *); /* <- s2 is assigned null here */ maxstart = MAX(maxstart, s2->firstvalid); /* <- SEGV here */ } va_end(marker); return (maxstart); } When the function is called with only one myStruct argument, it causes a SEGV. The code compiled and run without crashing on Windows XP when I compiled it using VS2005. I have now moved the code to Ubuntu Karmic and I am having problems with the stricter compiler on Linux. Is anyone able to spot what is causing the parameter not to be read correctly in the var_arg() statement? I am compiling using gcc version 4.4.1 Edit The statement that causes the SEGV is this one: start = getMaxStart(start, 1, ms1); The variables 'start' and 'ms1' have valid values when the code execution first reaches this line.

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• Preprocessor "macro function" vs. function pointer - best practice?

  - by Dustin

  I recently started a small personal project (RGB value to BGR value conversion program) in C, and I realised that a function that converts from RGB to BGR can not only perform the conversion but also the inversion. Obviously that means I don't really need two functions rgb2bgr and bgr2rgb. However, does it matter whether I use a function pointer instead of a macro? For example: int rgb2bgr (const int rgb); /* * Should I do this because it allows the compiler to issue * appropriate error messages using the proper function name, * not to mention possible debugging benefits? */ int (*bgr2rgb) (const int bgr) = rgb2bgr; /* * Or should I do this since it is merely a convenience * and they're really the same function anyway? */ #define bgr2rgb(bgr) (rgb2bgr (bgr)) I'm not necessarily looking for a change in execution efficiency as it's more of a subjective question out of curiosity. I am well aware of the fact that type safety is neither lost nor gained using either method. Would the function pointer merely be a convenience or are there more practical benefits to be gained of which I am unaware?

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