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  • Function pointers to member functions

    - by Jacob
    There are several duplicates of this but nobody explains why I can use a member variable to store the pointer (in FOO) but when I try it with a local variable (in the commented portion of BAR), it's illegal. Could anybody explain this? #include <iostream> using namespace std; class FOO { public: int (FOO::*fptr)(int a, int b); int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { fptr = &FOO::add_stuff; cout<<(this->*fptr)(a,b)<<endl; } }; class BAR { public: int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { //int (BAR::*fptr)(int a, int b); //fptr = &BAR::add_stuff; //cout<<(*fptr)(a,b)<<endl; } }; int main() { FOO test; test.call_adder(10,20); return 0; }

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  • c++ function overloading, making fwrite/fread act like PHP versions

    - by Newbie
    I'm used to the PHP fwrite/fread parameter orders, and i want to make them the same in C++ too. I want it to work with char and string types, and also any data type i put in it (only if length is defined). I am total noob on c++, this is what i made so far: size_t fwrite(FILE *fp, const std::string buf, const size_t len = SIZE_MAX){ if(len == SIZE_MAX){ return fwrite(buf.c_str(), 1, buf.length(), fp); }else{ return fwrite(buf.c_str(), 1, len, fp); } } size_t fwrite(FILE *fp, const void *buf, const size_t len = SIZE_MAX){ if(len == SIZE_MAX){ return fwrite((const char *)buf, 1, strlen((const char *)buf), fp); }else{ return fwrite(buf, 1, len, fp); } } Should this work just fine? And how should this be done if i wanted to do it the absolutely best possible way?

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  • Cryptic C++ "thing" (function pointer)

    - by m00st
    What is this syntax for in C++? Can someone point me to the technical term so I can see if I find anything in my text? At first I thought it was a prototype but then the = and (*fn) threw me off... Here is my example: void (*fn) (int&,int&) = x;

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  • C++ compilation error when passing a function into remove_if

    - by garsh0p
    So here's a snippet of my code. void RoutingProtocolImpl::removeAllInfinity() { dv.erase(std::remove_if(dv.begin(), dv.end(), hasInfCost), dv.end()); } bool RoutingProtocolImpl::hasInfCost(RoutingProtocolImpl::dv_entry *entry) { if (entry-link_cost == INFINITY_COST) { free(entry); return true; } else { return false; } } I'm getting the following error when compiling: RoutingProtocolImpl.cc:368: error: argument of type bool (RoutingProtocolImpl::)(RoutingProtocolImpl::dv_entry*)' does not matchbool (RoutingProtocolImpl::*)(RoutingProtocolImpl::dv_entry*)' Sorry, I'm kind of a C++ newb.

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  • Assigning function within function object without invoking the function itself.

    - by webzide
    Dear experts, I am trying to assign an function within an function object property without actually invoking then function itself. for instance, I have the following function object class definition function objectOne(name, value, id){ this.name=name; this.value=value; this.id=id; this.methodOne=methodFunction(this); } the last line this.methodOne=methodFunction(this); I want to pass the current object to the function but at the same time i don't want to execute the function right now. But if I do it this way without the bracket this.methodOne=methodFunction then the argument of this object would not be passed as a parameter to the function. Is there a way to work through this. Thank you in advance

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  • And now for a complete change of direction from C++ function pointers

    - by David
    I am building a part of a simulator. We are building off of a legacy simulator, but going in different direction, incorporating live bits along side of the simulated bits. The piece I am working on has to, effectively route commands from the central controller to the various bits. In the legacy code, there is a const array populated with an enumerated type. A command comes in, it is looked up in the table, then shipped off to a switch statement keyed by the enumerated type. The type enumeration has a choice VALID_BUT_NOT_SIMULATED, which is effectively a no-op from the point of the sim. I need to turn those no-ops into commands to actual other things [new simulated bits| live bits]. The new stuff and the live stuff have different interfaces than the old stuff [which makes me laugh about the shill job that it took to make it all happen, but that is a topic for a different discussion]. I like the array because it is a very apt description of the live thing this chunk is simulating [latching circuits by row and column]. I thought that I would try to replace the enumerated types in the array with pointers to functions and call them directly. This would be in lieu of the lookup+switch.

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  • Xpath help function

    - by NA
    Hi i have a document from which i am trying to extract a date. But the problem is within the node along with the date their is some text too. Something like <div class="postHeader"> Posted on July 20, 2009 9:22 PM PDT </div> From this tag i just want the date item not the Posted on text. something like ./xhtml:div[@class = 'postHeader'] is getting everything. and to be precise, the document i have is basically a nodelist of this elements for eg i will get 10 nodes of these elements with different date values but to be worse the problem is sometime inside these tags some random other tags also pops us like anchors etc. Can i write a universal expath which will just get the date out of the div tag?

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  • Function pointers uasage

    - by chaitanyavarma
    Hi All, Why these two codes give the same output, Case - 1: #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (x[0])(5,2); (x[1])(5,2); (x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10 Case -2 : #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (*x[0])(5,2); (*x[1])(5,2); (*x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10

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  • Function pointers usage

    - by chaitanyavarma
    Hi All, Why these two codes give the same output, Case 1: #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (x[0])(5,2); (x[1])(5,2); (x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10 Case 2 : #include <stdio.h> typedef void (*mycall) (int a ,int b); void addme(int a,int b); void mulme(int a,int b); void subme(int a,int b); main() { mycall x[10]; x[0] = &addme; x[1] = &subme; x[2] = &mulme; (*x[0])(5,2); (*x[1])(5,2); (*x[2])(5,2); } void addme(int a, int b) { printf("the value is %d\n",(a+b)); } void mulme(int a, int b) { printf("the value is %d\n",(a*b)); } void subme(int a, int b) { printf("the value is %d\n",(a-b)); } Output: the value is 7 the value is 3 the value is 10

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  • Recursive Syntax in Oslo

    - by Kevin Lawrence
    I'm writing my first DSL with Oslo and I am having a problem with a recursive syntax definition. The input has sections which can contain questions or other sections recursively (composite pattern) like this: Section: A Question: 1 Question: 2 Section: B Question: 1 End End My definition for a Section looks like this syntax Section = "Section:" id:Text body:(SectionBody)* "End Section"; Which works (but doesn't handle recursive sections) if I define SectionBody like this syntax SectionBody = (Question); but doesn't work with a recursive definition like this syntax SectionBody = (Question | Section); What am I missing?

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  • C# Function Inheritance--Use Child Class Vars with Base Class Function

    - by Sean O'Connor
    Good day, I have a fairly simple question to experienced C# programmers. Basically, I would like to have an abstract base class that contains a function that relies on the values of child classes. I have tried code similar to the following, but the compiler complains that SomeVariable is null when SomeFunction() attempts to use it. Base class: public abstract class BaseClass { protected virtual SomeType SomeVariable; public BaseClass() { this.SomeFunction(); } protected void SomeFunction() { //DO SOMETHING WITH SomeVariable } } A child class: public class ChildClass:BaseClass { protected override SomeType SomeVariable=SomeValue; } Now I would expect that when I do: ChildClass CC=new ChildClass(); A new instance of ChildClass should be made and CC would run its inherited SomeFunction using SomeValue. However, this is not what happens. The compiler complains that SomeVariable is null in BaseClass. Is what I want to do even possible in C#? I have used other managed languages that allow me to do such things, so I certain I am just making a simple mistake here. Any help is greatly appreciated, thank you.

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  • How do I create a partial function with generics in scala?

    - by Matteo Caprari
    Hello. I'm trying to write a performance measurements library for Scala. My idea is to transparently 'mark' sections so that the execution time can be collected. Unfortunately I wasn't able to bend the compiler to my will. An admittedly contrived example of what I have in mind: // generate a timing function val myTimer = mkTimer('myTimer) // see how the timing function returns the right type depending on the // type of the function it is passed to it val act = actor { loop { receive { case 'Int => val calc = myTimer { (1 to 100000).sum } val result = calc + 10 // calc must be Int self reply (result) case 'String => val calc = myTimer { (1 to 100000).mkString } val result = calc + " String" // calc must be String self reply (result) } Now, this is the farthest I got: trait Timing { def time[T <: Any](name: Symbol)(op: => T) :T = { val start = System.nanoTime val result = op val elapsed = System.nanoTime - start println(name + ": " + elapsed) result } def mkTimer[T <: Any](name: Symbol) : (() => T) => () => T = { type c = () => T time(name)(_ : c) } } Using the time function directly works and the compiler correctly uses the return type of the anonymous function to type the 'time' function: val bigString = time('timerBigString) { (1 to 100000).mkString("-") } println (bigString) Great as it seems, this pattern has a number of shortcomings: forces the user to reuse the same symbol at each invocation makes it more difficult to do more advanced stuff like predefined project-level timers does not allow the library to initialize once a data structure for 'timerBigString So here it comes mkTimer, that would allow me to partially apply the time function and reuse it. I use mkTimer like this: val myTimer = mkTimer('aTimer) val myString= myTimer { (1 to 100000).mkString("-") } println (myString) But I get a compiler error: error: type mismatch; found : String required: () => Nothing (1 to 100000).mkString("-") I get the same error if I inline the currying: val timerBigString = time('timerBigString) _ val bigString = timerBigString { (1 to 100000).mkString("-") } println (bigString) This works if I do val timerBigString = time('timerBigString) (_: String), but this is not what I want. I'd like to defer typing of the partially applied function until application. I conclude that the compiler is deciding the return type of the partial function when I first create it, chosing "Nothing" because it can't make a better informed choice. So I guess what I'm looking for is a sort of late-binding of the partially applied function. Is there any way to do this? Or maybe is there a completely different path I could follow? Well, thanks for reading this far -teo

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  • How to call a prototyped function from within the prototyped "class"?

    - by Jorge
    function FakeClass(){}; FakeClass.prototype.someMethod = function(){}; FakeClass.prototype.otherMethod = function(){ //need to call someMethod() here. } I need to call someMethod from otherMethod, but apparently it doesn't work. If i build it as a single function (not prototyped), i can call it, but calling a prototyped does not work. How can i do it as if i was treating the function just like a class method?

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  • Function inside .profile results in no log-in

    - by bioShark
    I've created a custom function in my .profile, and I've added right at the bottom, after my custom aliases : # custom functions function eclipse-gtk { cd ~/development/eclipse-juno ./eclipse_wb.sh & cd - } The function starts a custom version of my eclipse. After I've added it, because I didn't wanted to log-out/log-in, I've reloaded my profile with the command: . ~/.profile and then I've tested my function by calling eclipse-gtk and it worked without any issue. Today when I booted, I couldn't log in. After providing my password, in a few seconds I was back at the log-in screen. Dropping to command line using CTR + ALT + F1, I've commented out the function in my .profile and the log-in was possible without any issue. My question is, what did I do wrong when I wrote the function? And if there is something wrong, why did it work yesterday after reloading the profile. Thanks in advance. Using: Ubuntu 12.04

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  • wget recursive limited within subdomain

    - by Paul Seangwongree
    I want to download the following subdomain with the recursive option using wget: www.example.com/A/B So if that URL has links to www.example.com/A/B/C and www.example.com/A/B/D, these two should also be downloaded. But I don't want anything outside the www.example.com/A/B subdomain to be downloaded. For example, if www.example.com/A/B/C has a link back to www.example.com, the page www.example.com should not be downloaded. What wget command should I use?

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  • How to get SQL Function run a different query and return value from either query?

    - by RoguePlanetoid
    I need a function, but cannot seem to get it quite right, I have looked at examples here and elsewhere and cannot seem to get this just right, I need an optional item to be included in my query, I have this query (which works): SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR (1000),Description)) AS LenDesc FROM tblItem WHERE Title = @Title AND Manufacturer = @Manufacturer ORDER BY LenDesc DESC This works within a Function, however the Manufacturer is Optional for this search - which is to find the description of a similar item, if none is present, the other query is: SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR (1000),Description)) AS LenDesc FROM tblItem WHERE Title = @Title ORDER BY LenDesc DESC Which is missing the Manufacturer, how to I get my function to use either query based on the Manufacturer Value being present or not. The reason is I will have a function which first checks an SKU for a Description, if it is not present - it uses this method to get a Description from a Similar Product, then updates the product being added with the similar product's description. Here is the function so far: ALTER FUNCTION [dbo].[GetDescriptionByTitleManufacturer] ( @Title varchar(400), @Manufacturer varchar(160) ) RETURNS TABLE AS RETURN ( SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR (1000),Description)) AS LenDesc FROM tblItem WHERE Title = @Title AND Manufacturer = @Manufacturer ORDER BY LenDesc DESC ) I've tried adding BEGINs and IF...ELSEs but get errors or syntax problems each way I try it, I want to be able to do something like this pseudo-function (which does not work): ALTER FUNCTION [dbo].[GetDescriptionByTitleManufacturer] ( @Title varchar(400), @Manufacturer varchar(160) ) RETURNS TABLE AS BEGIN IF (@Manufacturer = Null) RETURN ( SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR (1000),Description)) AS LenDesc FROM tblItem WHERE Title = @Title ORDER BY LenDesc DESC ) ELSE RETURN ( SELECT TOP 100 PERCENT SKU, Description, LEN(CONVERT(VARCHAR (1000),Description)) AS LenDesc FROM tblItem WHERE Title = @Title AND Manufacturer = @Manufacturer ORDER BY LenDesc DESC ) END

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  • SQL SERVER – Introduction to PERCENTILE_DISC() – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    SQL Server 2012 introduces new analytical function PERCENTILE_DISC(). The book online gives following definition of this function: Computes a specific percentile for sorted values in an entire rowset or within distinct partitions of a rowset in Microsoft SQL Server 2012 Release Candidate 0 (RC 0). For a given percentile value P, PERCENTILE_DISC sorts the values of the expression in the ORDER BY clause and returns the value with the smallest CUME_DIST value (with respect to the same sort specification) that is greater than or equal to P. If you are clear with understanding of the function – no need to read further. If you got lost here is the same in simple words – find value of the column which is equal or more than CUME_DIST. Before you continue reading this blog I strongly suggest you read about CUME_DIST function over here Introduction to CUME_DIST – Analytic Functions Introduced in SQL Server 2012. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, CUME_DIST() OVER(PARTITION BY SalesOrderID ORDER BY ProductID ) AS CDist, PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS PercentileDisc FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: You can see that I have used PERCENTILE_DISC(0.5) in query, which is similar to finding median but not exactly. PERCENTILE_DISC() function takes a percentile as a passing parameters. It returns the value as answer which value is equal or great to the percentile value which is passed into the example. For example in above example we are passing 0.5 into the PERCENTILE_DISC() function. It will go through the resultset and identify which rows has values which are equal to or great than 0.5. In first example it found two rows which are equal to 0.5 and the value of ProductID of that row is the answer of PERCENTILE_DISC(). In some third windowed resultset there is only single row with the CUME_DIST() value as 1 and that is for sure higher than 0.5 making it as a answer. To make sure that we are clear with this example properly. Here is one more example where I am passing 0.6 as a percentile. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, CUME_DIST() OVER(PARTITION BY SalesOrderID ORDER BY ProductID ) AS CDist, PERCENTILE_DISC(0.6) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS PercentileDisc FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: The result of the PERCENTILE_DISC(0.6) is ProductID of which CUME_DIST() is more than 0.6. This means for SalesOrderID 43670 has row with CUME_DIST() 0.75 is the qualified row, resulting answer 773 for ProductID. I hope this explanation makes it further clear. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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