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  • How can I declare a pointer with filled information in C++?

    - by chacham15
    typedef struct Pair_s { char *first; char *second; } Pair; Pair pairs[] = { {"foo", "bar"}, //this is fine {"bar", "baz"} }; typedef struct PairOfPairs_s { Pair *first; Pair *second; } PairOfPairs; PairOfPairs pops[] = { {{"foo", "bar"}, {"bar", "baz"}}, //How can i create an equivalent of this NEATLY {&pairs[0], &pairs[1]} //this is not considered neat (imagine trying to read a list of 30 of these) }; How can I achieve the above style declaration semantics?

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  • How can I double-enhance a class with cglib?

    - by artemb
    Hi there! Here's the code: Patient patient = factory.createPatient(); Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(patient.getClass()); enhancer.setCallback(new DefaultMethodInterceptor(patient)); patient = (Patient) enhancer.create(); assertThat(patient.getFirstName()).isNotNull(); Enhancer enhancer2 = new Enhancer(); enhancer2.setSuperclass(patient.getClass()); enhancer2.setCallback(new DefaultMethodInterceptor(patient)); patient = (Patient) enhancer2.create(); assertThat(patient.getFirstName()).isNotNull(); It fails on the last assert with net.sf.cglib.core.CodeGenerationException: java.lang.reflect.InvocationTargetException-->null ... Caused by: java.lang.reflect.InvocationTargetException ... Caused by: java.lang.ClassFormatError: Duplicate method name&signature in class file my/package/entity/Patient$$EnhancerByCGLIB$$ca1e6685$$EnhancerByCGLIB$$f52743be I ask this because I want to enhance Hibernate's entities, but sometimes it returns already enhanced ones by itself and my second enhancement fails. How can I avoid this?

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  • How to use GPS data like the double value returned by getLatitude()?

    - by Dan
    I have been searching quite a bit for an answer, but maybe I'm just not using the correct terminology. I am creating an app that will access a database to return a list of other users that are within a certain distance of the users location. I've never worked with this type of data, and I don't really know what the values mean. I'd like to do all the calculations on the backend with either MySQL or PHP. Currently, I am storing the latitude and longitude as doubles within the database. I can access them and store them, but I have no idea how I might be able to sort them based on distance. Perhaps I should be using a different type or some technique that is common in this area. TIA.

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  • Assigning a pointer variable to a const int in C++?

    - by John
    I'm wondering if anyone can explain the following to me: If I write int i = 0; float* pf = i; I get a compile error (gcc 4.2.1): error: invalid conversion from ‘int’ to ‘float*’ Makes sense - they are obviously two completely different types. But if instead I write const int i = 0; float* pf = i; It compiles without error. Why should the 'const' make a difference on the right hand side of the assignment? Isn't part of the idea of the 'const' keyword to be able to enforce type constraints for constant values? Any explanation I have been able to come up with feels kind of bogus. And none of my explanations also explain the fact that const int i = 1; float* pf = i; fails to compile. Can anyone offer an explanation?

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  • how to specify a pointer to an overloaded function?

    - by davka
    I want to pass an overloaded function to the std::for_each() algorithm. e.g.: void f(char c); void f(int i); std::string s("example"); std::for_each(s.begin(), s.end(), f); I'd expect the compiler to resolve f() by the iterator type. Apparently, it (gcc 4.1.2) doesn't do it. So, how can I specify which f() I want? thanks a lot

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  • Double right click to Show a PopUpMenu with A TListView !!

    - by djiga4me
    Hi, I have a TListView and TPopupMenu, and I want to show a context menu when I right click on a TListItem. I tried the "AutoPopup" by assigning the component, but on a right click the PopupMenu is shown only and the wanted element is not selected. So i tried to use the "OnMouseDown", but we need to click and click again to show the menu on the wanted item. The first click is to select the item and the second shows the menu. But I want just a one click to do the two things. Do you have and idea about the problem? Thank you.

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  • Null pointer to struct which has zero size (empty)... It is a good practice?

    - by ProgramWriter
    Hi2All.. I have some null struct, for example: struct null_type { NullType& someNonVirtualMethod() { return *this; } }; And in some function i need to pass reference to this type. Reason: template <typename T1 = null_type, typename T2 = null_type, ... > class LooksLikeATupleButItsNotATuple { public: LooksLikeATupleButItsNotATuple(T1& ref1 = defParamHere, T2& ref2 = andHere..) : _ref1(ref1), _ref2(ref2), ... { } void someCompositeFunctionHere() { _ref1.someNonVirtualMethod(); _ref2.someNonVirtualMethod(); ... } private: T1& _ref1; T2& _ref2; ...; }; It is a good practice to use null reference as a default parameter?: *static_cast<NullType*>(0) It works on MSVC, but i have some doubts...

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  • Should I pointer-cast from a private derived class to its base class?

    - by skydoor
    I found this from C++FAQ Generally, No. From a member function or friend of a privately derived class, the relationship to the base class is known, and the upward conversion from PrivatelyDer* to Base* (or PrivatelyDer& to Base&) is safe; no cast is needed or recommended. However users of PrivatelyDer should avoid this unsafe conversion, since it is based on a private decision of PrivatelyDer, and is subject to change without notice. How to understand the above words? I don't think the explanation is correct or accurate. I have a code like this class A{ }; class B: private A{ }; int main(){ B *b = new B(); A *a = new A(); a = b; //wrong a = (A*)b; //right }

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  • Writting a getter for a pointer to a function .

    - by nomemory
    I have the following problem: "list.c" struct nmlist_element_s { void *data; struct nmlist_element_s *next; }; struct nmlist_s { nmlist_element *head; nmlist_element *tail; unsigned int size; void (*destructor)(void *data); int (*match)(const void *e1, const void *e2); }; /*** Other code ***/ What will be the signature for a function that returns 'destructor' ?

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  • Incorrect data when passing pointer a list of pointers to a function. (C++)

    - by Phil Elm
    I'm writing code for combining data received over multiple sources. When the objects received (I'll call them MyPacket for now), they are stored in a standard list. However, whenever I reference the payload size of a partial MyPacket, the value shows up as 1 instead of the intended size. Here's the function code: MyPacket* CombinePackets(std::list<MyPacket*>* packets, uint8* current_packet){ uint32 total_payload_size = 0; if(packets->size() <= 0) return NULL; //For now. std::list<MyPacket*>::iterator it = packets->begin(); //Some minor code here, not relevant to the problem. for(uint8 index = 0; index < packets->size(); index++){ //(*it)->GetPayloadSize() returns 1 when it should show 1024. I've tried directly accessing the variable and more, but I just can't get it to work. total_payload_size += (*it)->GetPayloadSize(); cout << "Adding to total payload size value: " << (*it)->GetPayloadSize() << endl; std::advance(it,1); } MyPacket* packet = new MyPacket(); //Byte is just a typedef'd unsigned char. packet->payload = (byte) calloc(total_payload_size, sizeof(byte)); packet->payload_size = total_payload_size; it = packets->begin(); //Go back to the beginning again. uint32 big_payload_index = 0; for(uint8 index = 0; index < packets->size(); index++){ if(current_packet != NULL) *current_packet = index; for(uint32 payload_index = 0; payload_index < (*it)->GetPayloadSize(); payload_index++){ packet->payload[big_payload_index] = (*it)->payload[payload_index]; big_payload_index++; } std::advance(it,1); } return packet; } //Calling code std::list<MyPacket*> received = std::list<MyPacket*>(); //The code that fills it is here. std::list<MyPacket*>::iterator it = received.begin(); cout << (*it)->GetPayloadSize() << endl; // Outputs 1024 correctly! MyPacket* final = CombinePackets(&received,NULL); cout << final->GetPayloadSize() << endl; //Outputs 181, which happens to be the number of elements in the received list. So, as you can see above, when I reference (*it)-GetPayloadSize(), it returns 1 instead of the intended 1024. Can anyone see the problem and if so, do you have an idea on how to fix this? I've spent 4 hours searching and trying new solutions, but they all keep returning 1... EDIT:

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  • MIPS return address in main

    - by Alexander
    I am confused why in the code below I need to decrement the stack pointer and store the return address again. If I don't do that... then PCSpim keeps on looping.. Why is that? ######################################################################################################################## ### main ######################################################################################################################## .text .globl main main: addi $sp, $sp, -4 # Make space on stack sw $ra, 0($sp) # Save return address # Start test 1 ############################################################ la $a0, asize1 # 1st parameter: address of asize1[0] la $a1, frame1 # 2nd parameter: address of frame1[0] la $a2, window1 # 3rd parameter: address of window1[0] jal vbsme # call function # Printing $v0 add $a0, $v0, $zero # Load $v0 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Printing $v1 add $a0, $v1, $zero # Load $v1 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall ############################################################ # End of test 1 lw $ra, 0($sp) # Restore return address addi $sp, $sp, 4 # Restore stack pointer jr $ra # Return ######################################################################################################################## ### vbsme ######################################################################################################################## #.text .globl vbsme vbsme: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address exit: add $v1, $t5, $zero # (v1) x coordinate of the block in the frame with the minimum SAD add $v0, $t4, $zero # (v0) y coordinate of the block in the frame with the minimum SAD lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer jr $ra # return If I delete: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address and lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer on vbsme: PCSpim keeps on running... Why??? I shouldn't have to increment/decrement the stack pointer on vbsme and then do the jr again right? The jal in main is supposed to handle that

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  • Using YQL multi-query & XPath to parse HTML, how to escape nested quotes?

    - by Tivac
    The title is more complicated than it has to be, here's the problem query. SELECT * FROM query.multi WHERE queries=" SELECT * FROM html WHERE url='http://www.stumbleupon.com/url/http://www.guildwars2.com' AND xpath='//li[@class=\"listLi\"]/div[@class=\"views\"]/a/span'; SELECT * FROM xml WHERE url='http://services.digg.com/1.0/endpoint?method=story.getAll&link=http://www.guildwars2.com'; SELECT * FROM json WHERE url='http://api.tweetmeme.com/url_info.json?url=http://www.guildwars2.com'; SELECT * FROM xml WHERE url='http://api.facebook.com/restserver.php?method=links.getStats&urls=http://www.guildwars2.com'; SELECT * FROM json WHERE url='http://www.reddit.com/button_info.json?url=http://www.guildwars2.com'" Specifically this line, xpath='//li[@class=\"listLi\"]/div[@class=\"views\"]/a/span' It's problematic because of the quoting, I have to nest them three levels deep and I've run out of quote characters to use. I've tried the following variations without success: //no attribute quoting xpath='//li[@class=listLi]/div[@class=views]/a/span' //try to quote attribute w/ backslash & single quote xpath='//li[@class=\'listLi\']/div[@class=\'views\']/a/span' //try to quote attribute w/ backslash & double quote xpath='//li[@class=\"listLi\"]/div[@class=\"views\"]/a/span' //try to quote attribute with double single quotes, like SQL xpath='//li[@class=''listLi'']/div[@class=''views'']/a/span' //try to quote attribute with double double quotes, like SQL xpath='//li[@class=""listLi""]/div[@class=""views""]/a/span' //try to quote attribute with quote entities xpath='//li[@class=&quot;listLi&quot;]/div[@class=&quot;views&quot;]/a/span' //try to surround XPath with backslash & double quote xpath=\"//li[@class='listLi']/div[@class='views']/a/span\" //try to surround XPath with double double quote xpath=""//li[@class='listLi']/div[@class='views']/a/span"" All without success. I don't see much out there about escaping XPath strings but everything I've found seems to be variations on using concat (which won't help because neither ' nor " are available) or html entities. Not using quotes for the attributes doesn't throw an error but fails because it's not the actual XPath string I need. I don't see anything in the YQL docs about how to handle escaping. I'm aware of how edge-casey this is but was hoping they'd have some sort of escaping guide.

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  • Function approximation with Maclaurin series

    - by marines
    I need to approx (1-x)^0.25 with given accuracy (0.0001 e.g.). I'm using expansion found on Wikipedia for (1+x)^0.25. I need to stop approximating when current expression is less than the accuracy. long double s(long double x, long double d) { long double w = 1; long double n = 1; // nth expression in series long double tmp = 1; // sum while last expression is greater than accuracy while (fabsl(tmp) >= d) { tmp *= (1.25 / n - 1) * (-x); // the next expression w += tmp; // is added to approximation n++; } return w; } Don't mind long double n. :P This works well when I'm not checking value of current expression but when I'm computing 1000 or more expressions. Domain of the function is <-1;1 and s() calculates approximation well for x in <-1;~0.6. The bigger the argument is the bigger is the error of calculation. From 0.6 it exceeds the accuracy. I'm not sure if the problem is clear enough because I don't know English math language well. The thing is what's the matter with while condition and why the function s() doesn't approximate correctly.

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  • Code Explanation (MPICH)

    - by user243680
    #include "mpi.h" #include <stdio.h> #include <math.h> double f(double a) { return (4.0 / (1.0 + a*a)); } void main(int argc, char *argv[]) { int done = 0, n, myid, numprocs,i; double PI25DT = 3.141592653589793238462643; double mypi, pi, h, sum, x; double startwtime, endwtime; int namelen; char processor_name[MPI_MAX_PROCESSOR_NAME]; MPI_Init(&argc,&argv); MPI_Comm_size(MPI_COMM_WORLD,&numprocs); MPI_Comm_rank(MPI_COMM_WORLD,&myid); MPI_Get_processor_name(processor_name,&namelen); fprintf(stderr,"Process %d on %s\n", myid, processor_name); fflush(stderr); n = 0; while (!done) { if (myid == 0) { printf("Enter the number of intervals: (0 quits) ");fflush(stdout); scanf("%d",&n); startwtime = MPI_Wtime(); } MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD); if (n == 0) done = 1; else { h = 1.0 / (double) n; sum = 0.0; for (i = myid + 1; i <= n; i += numprocs) { x = h * ((double)i - 0.5); sum += f(x); } mypi = h * sum; MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD); if (myid == 0) { printf("pi is approximately %.16f, Error is %.16f\n", pi, fabs(pi - PI25DT)); endwtime = MPI_Wtime(); printf("wall clock time = %f\n", endwtime-startwtime); } } } MPI_Finalize(); } Can anyone explain me the above code what it does??I am in lab and my miss has asked me to explain and i dont know what it is.please help

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  • how to rotate the Circle in DrawRect?

    - by senthilmuthu
    HI, i want to draw a circle in DrawRect through context like pie chart(took from tutorial) thorugh UITouch? i have given the code as follows,how can i rotate ? any help please? define PI 3.14159265358979323846 define snapshot_start 360 define snapshot_finish 360 static inline float radians(double degrees) { return degrees * PI / 180; } - (void)drawRect:(CGRect)rect { // Drawing code CGRect parentViewBounds = self.bounds; CGFloat x = CGRectGetWidth(parentViewBounds)/2; CGFloat y = CGRectGetHeight(parentViewBounds)*0.55; // Get the graphics context and clear it CGContextRef ctx = UIGraphicsGetCurrentContext(); CGContextClearRect(ctx, rect); // define stroke color CGContextSetRGBStrokeColor(ctx, 1, 1, 1, 1.0); // define line width CGContextSetLineWidth(ctx, 4.0); // need some values to draw pie charts double snapshotCapacity =20; double rawCapacity = 100; double systemCapacity = 1; int offset = 5; double pie1_start = 315.0; double pie1_finish = snapshotCapacity *360.0/rawCapacity; double system_finish = systemCapacity*360.0/rawCapacity; CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor greenColor] CGColor])); CGContextMoveToPoint(ctx, x+2*offset, y); CGContextAddArc(ctx, x+2*offset, y, 100, radians(snapshot_start), radians(snapshot_start+snapshot_finish), 0); CGContextClosePath(ctx); CGContextFillPath(ctx); // system capacity CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor colorWithRed:15 green:165/255 blue:0 alpha:1 ] CGColor])); CGContextMoveToPoint(ctx, x+offset,y); CGContextAddArc(ctx, x+offset, y, 100, radians(snapshot_start+snapshot_finish+offset), radians(snapshot_start+snapshot_finish+system_finish), 0); CGContextClosePath(ctx); CGContextFillPath(ctx); /* data capacity */ CGContextSetFillColor(ctx, CGColorGetComponents( [[UIColor colorWithRed:99/255 green:184/255 blue:255/255 alpha:1 ] CGColor])); CGContextMoveToPoint(ctx, x, y); CGContextAddArc(ctx, x, y, 100, radians(snapshot_start+snapshot_finish+system_finish+offset), radians(snapshot_start), 0); CGContextClosePath(ctx); CGContextFillPath(ctx); }

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  • Is it valid to use unsafe struct * as an opaque type instead of IntPtr in .NET Platform Invoke?

    - by David Jeske
    .NET Platform Invoke advocates declaring pointer types as IntPtr. For example, the following [DllImport("user32.dll")] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, Int32 lParam); However, I find when interfacing with interesting native interfaces, that have many pointer types, flattening everything into IntPtr makes the code very hard to read and removes the typical typechecking that a compiler can do. I've been using a pattern where I declare an unsafe struct to be an opaque pointer type. I can store this pointer type in a managed object, and the compiler can typecheck it form me. For example: class Foo { unsafe struct FOO {}; // opaque type unsafe FOO *my_foo; class if { [DllImport("mydll")] extern static unsafe FOO* get_foo(); [DllImport("mydll")] extern static unsafe void do_something_foo(FOO *foo); } public unsafe Foo() { this.my_foo = if.get_foo(); } public unsafe do_something_foo() { if.do_something_foo(this.my_foo); } While this example may not seem different than using IntPtr, when there are several pointer types moving between managed and native code, using these opaque pointer types for typechecking is a godsend. I have not run into any trouble using this technique in practice. However, I also have not seen an examples of anyone using this technique, and I wonder why. Is there any reason that the above code is invalid in the eyes of the .NET runtime? My main question is about how the .NET GC system treats "unsafe FOO *my_foo". Is this pointer something the GC system is going to try to trace, or is it simply going to ignore it? My hope is that because the underlying type is a struct, and it's declared unsafe, that the GC would ignore it. However, I don't know for sure. Thoughts?

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