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  • What are function pointers good for ?

    - by gramm
    Hi, I have trouble seing the utility of the function pointers. I guess it may be useful in some case (it exists, after all), but I can't think of a case where it's better or unavoidable to use a function pointer. Could you give some example of good use of function pointers (in C or C++)? Many thanks :)

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  • Python function correctly/incorrectly?

    - by Anthony Kernan
    I'm just starting too use python, learning experience. I know the basics logic of programming. I have a function in python that is running everytime, even when it's not supposed to. I use an if statement in the beginning of the function. I don't know why this if statement is not working, confused. I have another function that is similar and works correctly. Am I missing something simple? Here's the function that is not working... def check_artist_art(): if os.path.exists("/tmp/artistinfo") and open("/tmp/artistinfo").read() != title: #if artist == "": if os.path.exists(home + "/.artist"): os.remove(home + "/.artist") if os.path.exists("/tmp/artistinfo"): os.remove("/tmp/artistinfo") print artist return False else: os.path.exists("/tmp/artistinfo") and open("/tmp/artistinfo").read() == artist return False return True And this is the similar function that is working correctly.. def check_album(): if os.path.exists("/tmp/albuminfo") and open("/tmp/albuminfo").read() != album: if os.path.exists(home + "/.album"): os.remove(home + "/.album") if os.path.exists("/tmp/albuminfo"): os.remove("/tmp/albuminfo") return False elif os.path.exists("/tmp/trackinfo") and open("/tmp/trackinfo").read() == artist + album: return False return True Any help is greatly appreciated.

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  • I need help understanding how this jQuery filter function works, line-by-line, if possible

    - by user717236
    Here is the HTML: <div> <h3>text</h3> </div> <div> <h3>moretext</h3> </div> <div> <h3>123</h3> </div>?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? Here is the JS: var rv1_wlength = $("div").filter(function() { return $(this).find("h3").filter(function () { return $(this).text() != "123"; }).length; }); var rv1_wolength = $("div").filter(function() { return $(this).find("h3").filter(function () { return $(this).text() != "123"; }); }); var rv2 = $("div").find("h3").filter(function() { return $(this).text() != "123"; }); alert(rv1_wlength.text()); // text // moretext alert(rv1_wolength.text()); // text // moretext // 123 alert(rv2.text());? // textmoretext I don't understand why the first two methods print the elements on each line, whereas the second method concatenates them. "rv2" is a jQuery object. Then, what are the first two (rv1_wlength and rv1_wolength)? Furthermore, I don't understand why the inclusion of the length property makes all the difference in filtering the elements. The second method does nothing, since it returns all the elements. The first method, with the only change being the addition of the length property, correctly filters the elements. I would very much like a line-by-line explanation. I would sincerely appreciate any feedback. Thank you.

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  • C++ inheritance and member function pointers

    - by smh
    In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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  • pointer to const member function typedef

    - by oldcig
    I know it's possible to separate to create a pointer to member function like this struct K { void func() {} }; typedef void FuncType(); typedef FuncType K::* MemFuncType; MemFuncType pF = &K::func; Is there similar way to construct a pointer to a const function? I've tried adding const in various places with no success. I've played around with gcc some and if you do template deduction on something like template <typename Sig, typename Klass> void deduce(Sig Klass::*); It will show Sig with as a function signature with const just tacked on the end. If to do this in code it will complain that you can't have qualifiers on a function type. Seems like it should be possible somehow because the deduction works.

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  • removing dependancy of a private function inside a public function using Rhino Mocks

    - by L G
    Hi All, I am new to mocking, and have started with Rhino Mocks. My scenario is like this..in my class library i have a public function and inside it i have a private function call, which gets output from a service.I want to remove the private function dependency. public class Employee { public virtual string GetFullName(string firstName, string lastName) { string middleName = GetMiddleName(); return string.Format("{0} {2} {1}", firstName, lastName,middleName ); } private virtual string GetMiddleName() { // Some call to Service return "George"; } } This is not my real scenario though, i just wanted to know how to remove dependency of GetMiddleName() function and i need to return some default value while unit testing. Note : I won't be able to change the private function here..or include Interface..Keeping the functions as such, is there any way to mock this.Thank

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  • Passing a pointer to a function that doesn't match the requirements of the formal parameter

    - by Andreas Grech
    int valid (int x, int y) { return x + y; } int invalid (int x) { return x; } int func (int *f (int, int), int x, int y) { //f is a pointer to a function taking 2 ints and returning an int return f(x, y); } int main () { int val = func(valid, 1, 2), inval = func(invalid, 1, 2); // <- 'invalid' does not match the contract printf("Valid: %d\n", val); printf("Invalid: %d\n", inval); /* Output: * Valid: 3 * Invalid: 1 */ } At the line inval = func(invalid, 1, 2);, why am I not getting a compiler error? If func expects a pointer to a function taking 2 ints and I pass a pointer to a function that takes a single int, why isn't the compiler complaining? Also, since this is happening, what happens to the second parameter y in the invalid function?

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  • Giving my function access to outside variable

    - by brett
    I have an array outside: $myArr = array(); I would like to give my function access to the array outside it so it can add values to it function someFuntion(){ $myVal = //some processing here to determine value of $myVal $myArr[] = $myVal; } How do I give the function the right scoping to the variable?

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  • How to catch unintentional function interpositioning?

    - by SiegeX
    Reading through my book Expert C Programming, I came across the chapter on function interpositioning and how it can lead to some serious hard to find bugs if done unintentionally. The example given in the book is the following: my_source.c mktemp() { ... } main() { mktemp(); getwd(); } libc mktemp(){ ... } getwd(){ ...; mktemp(); ... } According to the book, what happens in main() is that mktemp() (a standard C library function) is interposed by the implementation in my_source.c. Although having main() call my implementation of mktemp() is intended behavior, having getwd() (another C library function) also call my implementation of mktemp() is not. Apparently, this example was a real life bug that existed in SunOS 4.0.3's version of lpr. The book goes on to explain the fix was to add the keyword static to the definition of mktemp() in my_source.c; although changing the name altogether should have fixed this problem as well. This chapter leaves me with some unresolved questions that I hope you guys could answer: Does GCC have a way to warn about function interposition? We certainly don't ever intend on this happening and I'd like to know about it if it does. Should our software group adopt the practice of putting the keyword static in front of all functions that we don't want to be exposed? Can interposition happen with functions introduced by static libraries? Thanks for the help. EDIT I should note that my question is not just aimed at interposing over standard C library functions, but also functions contained in other libraries, perhaps 3rd party, perhaps ones created in-house. Essentially, I want to catch any instance of interpositioning regardless of where the interposed function resides.

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  • Function name inside a variable

    - by John Doe
    Hello. I have a simple question (i guess). I'm getting the name of the function inside a variable from database. After that, i want to run the specific function. How can i echo the function's name inside the php file? The code is something like this: $variable= get_specific_option; //execute function $variable_somesuffix(); The "somesuffix" will be a simple text. I tried all the things i had in mind but nothing worked.

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  • calling function in radiobutton group

    - by vijisai
    thank you very much. with your help, i am now able to call the function for each radio button. however, i get a error message Reference to non-existent field 'ics_si' ics_si is my function, which has the following code, i do not know where i am making a mistake i have created the edit box for user to input the values for bore and stroke. and vdisp is calculated and the result is displayed in the third edit box. function ics_si_Callback(hObject, eventdata, handles) b = str2double(get(handles.bore,'String')); s = str2double(get(handles.stroke,'String')); vdisp = (pi * b * b * s*10^(-3))/4; set(handles.vdisp,'String',vdisp); this code must be called when i press the first or second radio button. i.e. when the radio button is pressed, it should call the function ics_si, calculate it and display the result. how to get this.

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  • Pass variable name to a function in r

    - by Misha
    Is it possible to pass just a variable name in a function call and have it utilised as such within the function?? pseudocode: q<-function(A){ b<-(w%in%A.2|w%in%A.7) factor(b,levels=c(F,T),labels=c("non-"A,A))} w<-c(0:10) e.2<-c(1,2) e.7<-c(6,7) what I´d like to do is q(e) and have returned non-e,e,e,non-e,non-e,e,e,non-e,non-e //M q<-function(A) { a2<-get(paste(a,".2",sep="")) a7<-get(paste(a,".7",sep="")) b<-(w%in%a2|%in%a7) factor(b,levels=c(F,T),labels=c(paste("non-",a,sep=""),a)) } q("e") Thx, M

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  • How to pass function reference into arguments

    - by Ockonal
    Hi, I'm using boost::function for making function-references: typedef boost::function<void (SomeClass &handle)> Ref; someFunc(Ref &pointer) {/*...*/} void Foo(SomeClass &handle) {/*...*/} What is the best way to pass Foo into the someFunc? I tried something like: someFunc(Ref(Foo));

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  • Constructing a function call in C

    - by 0x6adb015
    Given that I have a pointer to a function (provided by dlsym() for example) and a linked list of typed arguments, how can I construct a C function call with those arguments? Example: struct param { enum type { INT32, INT64, STRING, BOOL } type; union { int i32; long long i64; char *str; bool b; } value; struct param *next; }; int call_this(int (*function)(), struct param *args) { int result; /* magic here that calls function(), which has a prototype of f(int, long long, char *, bool); , when args consist of a linked list of INT32, INT64, STRING, BOOL types. */ return result; } The OS is Linux. I would like the solution to be portable across MIPS, PPC and x86 (all 32 bits) architecture, using GCC as the compiler. Thanks!

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  • How to store a function in a member of class? (Using function as callback)

    - by Dane
    I want to store a function as a class member and call it inside the class? Pretty much like a callback function. My class draw a document but every document must drawn differently. So I want to assign a function (written outside of the class) into one of the members of the class and then call it when I want to draw the document. This function mostly is responsible for transforming objects according to each specific document. Here is my class: class CDocument { public: CDocument(); ~CDocument(); void *TransFunc(); } void Transform() { } int main() CDocument* Doc = new CDocument(); Doc->TransFunc = Transform(); } I know that this is probably simple question, but I couldn't find the answer by googling or searching SO.

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  • What is the point of function pointers?

    - by gramm
    Hi, I have trouble seing the utility of the function pointers. I guess it may be useful in some cases (they exist, after all), but I can't think of a case where it's better or unavoidable to use a function pointer. Could you give some example of good use of function pointers (in C or C++)? Many thanks :)

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  • Syncronizing indices of function pointer table to table contents

    - by Thomas Matthews
    In the embedded system I'm working on, we are using a table of function pointers to support proprietary Dynamic Libraries. We have a header file that uses named constants (#define) for the function pointer indices. These values are used in calculating the location in the table of the function's address. Example: *(export_table.c)* // Assume each function in the table has an associated declaration typedef void (*Function_Ptr)(void); Function_Ptr Export_Function_Table[] = { 0, Print, Read, Write, Process, }; Here is the header file: *export_table.h* #define ID_PRINT_FUNCTION 1 #define ID_READ_FUNCTION 2 #define ID_WRITE_FUNCTION 3 #define ID_PROCESS_FUNCTION 4 I'm looking for a scheme to define the named constants in terms of their location in the array so that when the order of the functions changes, the constants will also change. (Also, I would like the compiler or preprocessor to calculate the indices to avoid human mistakes like typeo's.)

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  • Hashing a python function to regenerate output when the function is modified

    - by Seth Johnson
    I have a python function that has a deterministic result. It takes a long time to run and generates a large output: def time_consuming_function(): # lots_of_computing_time to come up with the_result return the_result I modify time_consuming_function from time to time, but I would like to avoid having it run again while it's unchanged. [time_consuming_function only depends on functions that are immutable for the purposes considered here; i.e. it might have functions from Python libraries but not from other pieces of my code that I'd change.] The solution that suggests itself to me is to cache the output and also cache some "hash" of the function. If the hash changes, the function will have been modified, and we have to re-generate the output. Is this possible or ridiculous? Updated: based on the answers, it looks like what I want to do is to "memoize" time_consuming_function, except instead of (or in addition to) arguments passed into an invariant function, I want to account for a function that itself will change.

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  • Set the output of a function equal to a variable

    - by ryno
    How would i set the output of a custom php function to a variable? The function is: function getRandomColor1() { global $cols; $num_cols = count($cols); $rand = array_rand($cols); $rand_col = $cols[$rand]; echo $rand_col; unset($cols[$rand]); } How would i set getRandomColor1 equal to $RandomColor1? I need it to be a variable so I can use it in css like: #boxone1 { height: 150px; width: 150px; background: <?=$RandomColor1?>; float: left; } If its not possible to set it as a variable, how else could i put the output of the function into css?

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  • Query with UDF works in Access but gives Undefined function in expression (Err 3085) in Excel

    - by ronwest
    I have an Access table with a date/time field. I wanted to make a composite Key field out of the date/time field and 3 other text fields in the same format as the matching Key field in another database. So I concatenated the 3 text fields and wrote a User-Defined-Function in a Module to output the date field as a string in the format "YYYYMMDD". Public Function YYYYMMDD(dteDate As Date) As String YYYYMMDD = Format(dteDate, "YYYYMMDD") End Function I can then successfully run my queries in Access and it all works fine. But when I set up some DAO code in Excel and try to run the query that works fine within Access... db.Execute "qryMake_tblValsDailyAccount" ...Excel gives me the "Undefined function in expression. (Error 3085)" error. To me this is a bug in Excel and/or Access, because the (Excel) client shouldn't need to know anything about the internal calculations that normally take place perfectly in the (Access) server when in isolation. Excel should send the querydef (name with no parameters) to the server, let the server do its work then receive the answers. Why does it need to get involved with a function internal to the server? Does anyone know a way around this?

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  • C++: How do I pass a function(without knowing its parameters) to another function?

    - by Ninja
    Hi all. I'm trying to create a function that will store and repeat another function given as a parameter for a specific amount of time or repeats given. But when you want to pass a function as a parameter you have to know all of its parameters before hand. How would I do if I wanted to pass the function as one parameter, and the parameters as another? void AddTimer(float time, int repeats, void (*func), params); // I know params has no type and that (*func) is missing parameters but it is just to show you what I mean Thanks in advance

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