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  • Default template arguments for function templates

    - by Arman
    Why are default template arguments only allowed on class templates? Why can't we define a default type in a member function template? For example: struct mycclass { template<class T=int> void mymember(T* vec) { // ... } }; Instead, C++ forces that default template arguments are only allowed on a class template.

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  • How to display variables in Taglist window in vim

    - by Yogesh Arora
    I am using Taglist plugin in vim. In the taglist window i can see tags like namespaces, classes, struct, function but not variables. I saw a screenshot(attached below) on Taglist website which had this info. I am using Vim 7 and Exuberant Ctags 5.8, and i have generated my ctags using this command ctags --c++-kinds=+p --fields=+iaS --extra=+q --language-force=C++

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  • Getting syntax errors when building with python 3.1 and not with python 2.6

    - by mathan
    Hi All, Using Mac os X 10.6, python 3.1 and gcc 4.0 trying to build pyfsevent implemented in python2.6 by converting it to python 3.1. Wondering when getting the following errors while building in python 3.1 alone. Why not when building with python 2.6? error: syntax error before ‘CFFileDescriptorRef’ warning: no semicolon at end of struct or union error: syntax error before ‘}’ token warning: data definition has no type or storage clas

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  • How to start new browser window in cpecified location whith cpecified size

    - by Pritorian
    Hi all! I create a new instance and trying to resize new instance of browser like this: [System.Runtime.InteropServices.DllImport("user32.dll")] private static extern bool GetWindowInfo(IntPtr hwnd, ref tagWINDOWINFO pwi); [System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)] public struct tagRECT { /// LONG->int public int left; /// LONG->int public int top; /// LONG->int public int right; /// LONG->int public int bottom; } [System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)] public struct tagWINDOWINFO { /// DWORD->unsigned int public uint cbSize; /// RECT->tagRECT public tagRECT rcWindow; /// RECT->tagRECT public tagRECT rcClient; /// DWORD->unsigned int public uint dwStyle; /// DWORD->unsigned int public uint dwExStyle; /// DWORD->unsigned int public uint dwWindowStatus; /// UINT->unsigned int public uint cxWindowBorders; /// UINT->unsigned int public uint cyWindowBorders; /// ATOM->WORD->unsigned short public ushort atomWindowType; /// WORD->unsigned short public ushort wCreatorVersion; } [System.Runtime.InteropServices.DllImport("user32.dll")] private static extern bool MoveWindow(IntPtr hWnd, int X, int Y, int nWidth, int nHeight, bool bRepaint); [System.Runtime.InteropServices.DllImport("user32.dll")] private static extern bool UpdateWindow(IntPtr hWnd); private void button2_Click(object sender, EventArgs e) { using (System.Diagnostics.Process browserProc = new System.Diagnostics.Process()) { browserProc.StartInfo.FileName = webBrowser1.Url.ToString(); browserProc.StartInfo.WindowStyle = System.Diagnostics.ProcessWindowStyle.Minimized; int i= browserProc.Id; tagWINDOWINFO info = new tagWINDOWINFO(); info.cbSize = (uint)System.Runtime.InteropServices.Marshal.SizeOf(info); browserProc.Start(); GetWindowInfo(browserProc.MainWindowHandle, ref info); browserProc.WaitForInputIdle(); string str = browserProc.MainWindowTitle; MoveWindow(browserProc.MainWindowHandle, 100, 100, 100, 100, true); UpdateWindow(browserProc.MainWindowHandle); } } But I get an "No process is associated with this object". Could anyone help? Or mb other ideas how to run new browser window whith specified size and location?

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  • Compilation errors for a c api

    - by sam
    What would be the reason for the following errors though the syntax was right and I have included the coreservices framework in which some data type and constants are declared. " c.c:22: error: syntax error before ‘CFFileDescriptorRef’ c.c:22: warning: no semicolon at end of struct or union c.c:24: error: syntax error before ‘}’ token c.c:24: warning: data definition has no type or storage class lipo: can't figure out the architecture type of: /var/folders/fF/fFgga6+-E48RL+iXKLFmAE+++TI/-Tmp-//ccFzQIAj.out "

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  • Efficiency of data structures in C99 (possibly affected by endianness)

    - by Ninefingers
    Hi All, I have a couple of questions that are all inter-related. Basically, in the algorithm I am implementing a word w is defined as four bytes, so it can be contained whole in a uint32_t. However, during the operation of the algorithm I often need to access the various parts of the word. Now, I can do this in two ways: uint32_t w = 0x11223344; uint8_t a = (w & 0xff000000) >> 24; uint8_t b = (w & 0x00ff0000) >> 16; uint8_t b = (w & 0x0000ff00) >> 8; uint8_t d = (w & 0x000000ff); However, part of me thinks that isn't particularly efficient. I thought a better way would be to use union representation like so: typedef union { struct { uint8_t d; uint8_t c; uint8_t b; uint8_t a; }; uint32_t n; } word32; Using this method I can assign word32 w = 0x11223344; then I can access the various parts as I require (w.a=11 in little endian). However, at this stage I come up against endianness issues, namely, in big endian systems my struct is defined incorrectly so I need to re-order the word prior to it being passed in. This I can do without too much difficulty. My question is, then, is the first part (various bitwise ands and shifts) efficient compared to the implementation using a union? Is there any difference between the two generally? Which way should I go on a modern, x86_64 processor? Is endianness just a red herring here? I could inspect the assembly output of course, but my knowledge of compilers is not brilliant. I would have thought a union would be more efficient as it would essentially convert to memory offsets, like so: mov eax, [r9+8] Would a compiler realise that is what happening in the bit-shift case above? If it matters, I'm using C99, specifically my compiler is clang (llvm). Thanks in advance.

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  • ANSI C blackjack assignment, linux GCC compiler, i'm stuck...

    - by Bill Adams
    Here's what i have so far... I have yet to figure out how i'm going to handle the 11 / 1 situation with an ace, and when the player chooses an option for hit/stand, i get segfault. HELP!!! #include <stdio.h> #include <string.h> #include <stdlib.h> #include <time.h> #define DECKSIZE 52 #define VALUE 9 #define FACE 4 #define HANDSIZE 26 typedef struct { int value; char* suit; char* name; }Card; typedef struct { int value; char* suit; char* name; }dealerHand; typedef struct { int value; char* suit; char* name; }playerHand; Card cards[DECKSIZE]; dealerHand deal[HANDSIZE]; playerHand dealt[HANDSIZE]; char *faceName[]={"two","three", "four","five","six", "seven","eight","nine", "ten", "jack","queen", "king","ace"}; char *suitName[]={"spades","diamonds","clubs","hearts"}; void printDeck(){ int i; for(i=0;i<DECKSIZE;i++){ printf("%s of %s value = %d\n ",cards[i].name,cards[i].suit,cards[i].value); if((i+1)%13==0 && i!=0) printf("-------------------\n\n"); } } void shuffleDeck(){ srand(time(NULL)); int this; int that; Card temp; int c; for(c=0;c<10000;c++){ //c is the index for number of individual card shuffles should be set to c<10000 or more this=rand()%DECKSIZE; that=rand()%DECKSIZE; temp=cards[this]; cards[this]=cards[that]; cards[that]=temp; } } /*void hitStand(i,y){ // I dumped this because of a segfault i couldn't figure out. int k; printf(" Press 1 to HIT or press 2 to STAND:"); scanf("%d",k); if(k=1){ dealt[y].suit=cards[i].suit; dealt[y].name=cards[i].name; dealt[y].value=cards[i].value; y++; i++; } } */ int main(){ int suitCount=0; int faceCount=0; int i; int x; int y; int d; int p; int k; for(i=0;i<DECKSIZE;i++){ //this for statement builds the deck if(faceCount<9){ cards[i].value=faceCount+2; }else{ //assigns face cards as value 10 cards[i].value=10; } cards[i].suit=suitName[suitCount]; cards[i].name=faceName[faceCount++]; if(faceCount==13){ //this if loop increments suit count once cards[i].value=11; //all faces have been assigned, and also suitCount++; //assigns the ace as 11 faceCount=0; } //end building deck } /*printDeck(); //prints the deck in order shuffleDeck(); //shuffles the deck printDeck(); //prints the deck as shuffled This was used in testing, commented out to keep the deck hidden!*/ shuffleDeck(); x=0; y=0; for(i=0;i<4;i++){ //this for loop deals the first 4 cards, dealt[y].suit=cards[i].suit; //first card to player, second to dealer, dealt[y].name=cards[i].name; //as per standard dealing practice. dealt[y].value=cards[i].value; i++; y++; deal[x].suit=cards[i].suit; deal[x].name=cards[i].name; deal[x].value=cards[i].value; x++; } printf(" Dealer's hand is: %s of %s and XXXX of XXXX. (Second card is hidden!)\n",deal[0].name,deal[0].suit,deal[1].name,deal[1].suit); printf(" Player's hand is: %s of %s and %s of %s.\n",dealt[0].name,dealt[0].suit,dealt[1].name,dealt[1].suit); printf(" the current value of the index i=%d\n",i); //this line gave me the value of i for testing d=deal[0].value+deal[1].value; p=dealt[0].value+dealt[1].value; if(d==21){ printf(" The Dealer has Blackjack! House win!\n"); }else{ if(d>21){ printf(" The dealer is Bust! You win!\n"); }else{ if(d>17){ printf(" Press 1 to HIT or 2 to STAND"); scanf("%d",k); if(k==1){ dealt[y].suit=cards[i].suit; dealt[y].name=cards[i].name; dealt[y].value=cards[i].value; y++; i++; } }else{ if(d<17){ printf(" Dealer Hits!"); deal[x].suit=cards[i].suit; deal[x].name=cards[i].name; deal[x].value=cards[i].value; x++; i++; } } } } return 0; }

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  • POD global object initialization

    - by paercebal
    I've got bitten today by a bug. The following source can be copy/pasted (and then compiled) into a main.cpp file #include <iostream> // The point of SomeGlobalObject is for its // constructor to be launched before the main // ... struct SomeGlobalObject { SomeGlobalObject() ; } ; // ... // Which explains the global object SomeGlobalObject oSomeGlobalObject ; // A POD... I was hoping it would be constructed at // compile time when using an argument list struct MyPod { short m_short ; const char * const m_string ; } ; // declaration/Initialization of a MyPod array MyPod myArrayOfPod[] = { { 1, "Hello" }, { 2, "World" }, { 3, " !" } } ; // declaration/Initialization of an array of array of void * void * myArrayOfVoid[][2] = { { (void *)1, "Hello" }, { (void *)2, "World" }, { (void *)3, " !" } } ; // constructor of the global object... Launched BEFORE main SomeGlobalObject::SomeGlobalObject() { std::cout << "myArrayOfPod[0].m_short : " << myArrayOfPod[0].m_short << std::endl ; std::cout << "myArrayOfVoid[0][0] : " << myArrayOfVoid[0][0] << std::endl ; } // main... What else ? int main(int argc, char* argv[]) { return 0 ; } MyPod being a POD, I believed there would be no constructors. Only initialization at compile time. Thus, the global object SomeGlobalObject would have no problem to use the global array of PODs upon its construction. The problem is that in real life, nothing is so simple. On Visual C++ 2008 (I did not test on other compilers), upon execution myArrayOfPodis not initialized, even ifmyArrayOfVoid` is initialized. So my questions is: Are C++ compilers not supposed to initialize global PODs (including POD structures) at compilation time ? Note that I know global variable are evil, and I know that one can't be sure of the order of creation of global variables declared in different compilation units. The problem here is really the POD C-like initialization which seems to call a constructor (the default, compiler-generated one?). And to make everyone happy: This is on debug. On release, the global array of PODs is correctly initialized.

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  • Pointless 'MIDL_INTERFACE' Macro in winapi?

    - by nebukadnezzar
    After browsing some old code, I noticed that some classes are defined in this manner: MIDL_INTERFACE("XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX") Classname: public IUnknown { /* classmembers ... */ }; However, the macro MIDL_INTERFACE is defined as: #define MIDL_INTERFACE(x) struct in C:/MinGW/include/rpcndr.h (somewhere around line 17). The macro itself is rather obviously entirely pointless, so what's the true purpose of this macro?

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  • Uses of a C++ Arithmetic Promotion Header

    - by OlduvaiHand
    I've been playing around with a set of templates for determining the correct promotion type given two primitive types in C++. The idea is that if you define a custom numeric template, you could use these to determine the return type of, say, the operator+ function based on the class passed to the templates. For example: // Custom numeric class template <class T> struct Complex { Complex(T real, T imag) : r(real), i(imag) {} T r, i; // Other implementation stuff }; // Generic arithmetic promotion template template <class T, class U> struct ArithmeticPromotion { typedef typename X type; // I realize this is incorrect, but the point is it would // figure out what X would be via trait testing, etc }; // Specialization of arithmetic promotion template template <> class ArithmeticPromotion<long long, unsigned long> { typedef typename unsigned long long type; } // Arithmetic promotion template actually being used template <class T, class U> Complex<typename ArithmeticPromotion<T, U>::type> operator+ (Complex<T>& lhs, Complex<U>& rhs) { return Complex<typename ArithmeticPromotion<T, U>::type>(lhs.r + rhs.r, lhs.i + rhs.i); } If you use these promotion templates, you can more or less treat your user defined types as if they're primitives with the same promotion rules being applied to them. So, I guess the question I have is would this be something that could be useful? And if so, what sorts of common tasks would you want templated out for ease of use? I'm working on the assumption that just having the promotion templates alone would be insufficient for practical adoption. Incidentally, Boost has something similar in its math/tools/promotion header, but it's really more for getting values ready to be passed to the standard C math functions (that expect either 2 ints or 2 doubles) and bypasses all of the integral types. Is something that simple preferable to having complete control over how your objects are being converted? TL;DR: What sorts of helper templates would you expect to find in an arithmetic promotion header beyond the machinery that does the promotion itself?

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  • other way to add item do List<>

    - by netmajor
    In my other ask You can see code of my arr structure and PriorityQueue collection. I normally add items to this collection like that: arr.PriorityQueue.Add(new element((value(item, endPoint) + value(startPoint, item)),item)); I am curious that is other way to do this (add element(which is struct) object to List) ? In lambda way for example ? I just eager for knowledge :)

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  • Overload dereference operator

    - by zilgo
    I'm trying to overload the dereference operator, but compiling the following code results in the error 'initializing' : cannot convert from 'X' to 'int': struct X { void f() {} int operator*() const { return 5; } }; int main() { X* x = new X; int t = *x; delete x; return -898; } What am I doing wrong?

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  • Why doesn't ADL find function templates?

    - by Huw Giddens
    What part of the C++ specification restricts argument dependent lookup from finding function templates in the set of associated namespaces? In other words, why won't the following compile? namespace ns { struct foo {}; template<int i> void frob(foo const&) {} } int main() { ns::foo f; frob<0>(f); }

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  • How to read direct3d texture pixels

    - by Mr Bell
    So I have a x8r8g8b8 formatted IDirect3DSurface9 that contains the contents of the back buffer. When I call LockRect on it I get access to a struct containing pBits, a pointer to the pixels I assume, and and integer Pitch (which I am very unclear about its purpose). How to read the individual pixels? Visual Studio 2008 C++

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  • conversion of DNA to Protein - c structure issue

    - by sam
    I am working on conversion of DNA sequence to Protein sequence. I had completed all program only one error I found there is of structure. dna_codon is a structure and I am iterating over it.In first iteration it shows proper values of structure but from next iteration, it dont show the proper value stored in structure. Its a small error so do not think that I havnt done anything and downvote. I am stucked here because I am new in c for structures. CODE : #include <stdio.h> #include<string.h> void main() { int i, len; char short_codons[20]; char short_slc[1000]; char sequence[1000]; struct codons { char amino_acid[20], slc[20], dna_codon[40]; }; struct codons c1 [20]= { {"Isoleucine", "I", "ATT, ATC, ATA"}, {"Leucine", "L", "CTT, CTC, CTA, CTG, TTA, TTG"}, {"Valine", "V", "GTT, GTC, GTA, GTG"}, {"Phenylalanine", "F", "TTT, TTC"}, {"Methionine", "M", "ATG"}, {"Cysteine", "C", "TGT, TGC"}, {"Alanine", "A", "GCT, GCC, GCA, GCG"}, {"Proline", "P", "CCT, CCC, CCA,CCG "}, {"Threonine", "T", "ACT, ACC, ACA, ACG"}, {"Serine", "S", "TCT, TCC, TCA, TCG, AGT, AGC"}, {"Tyrosine", "Y", "TAT, TAC"}, {"Tryptophan", "W", "TGG"}, {"Glutamine", "Q", "CAA, CAG"}, {"Aspargine","N" "AAT, AAC"}, {"Histidine", "H", "CAT, CAC"}, {"Glutamic acid", "E", "GAA, GAG"}, {"Aspartic acid", "D", "GAT, GAC"}, {"Lysine", "K", "AAA, AAG"}, {"Arginine", "R", "CGT, CGC, CGA, CGG, AGA, AGG"}, {"Stop codons", "Stop", "AA, TAG, TGA"} }; int count = 0; printf("Enter the sequence: "); gets(sequence); char *input_string = sequence; char *tmp_str = input_string; int k; char *pch; while (*input_string != '\0') { char string_3l[4] = {'\0'}; strncpy(string_3l, input_string, 3); printf("\n-----------%s & %s----------", string_3l, tmp_str ); for(k=0;k<20;k++) { //printf("@REAL - %s", c1[0].dna_codon); printf("@ %s", c1[k].dna_codon); int x; x = c1[k].dna_codon; pch = strtok(x, ","); while (pch != NULL) { printf("\n%d : %s with %s", k, string_3l, pch); count=strcmp(string_3l, pch); if(count==0) { strcat(short_slc, c1[k].slc); printf("\n==>%s", short_slc); } pch = strtok (NULL, " ,.-"); } } input_string = input_string+3; } printf("\nProtien sequence is : %s\n", short_slc); } INPUT : TAGTAG OUTPUT : If you see output of printf("\n-----------%s & %s----------", string_3l, tmp_str ); in both iterations, we found that values defined in structure are reduced. I want to know why structure reduces it or its my mistake? because I am stucked here

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  • Problem getting correct parameters for C# P/Invoke call to C++ dll

    - by Jim Jones
    Trying to Interop a functionality from the Outside In API from Oracle. Have the following function: SCCERR EXOpenExport {VTHDOC hDoc, VTDWORD dwOutputId, VTDWORD dwSpecType, VTLPVOID pSpec, VTDWORD dwFlags, VTSYSPARAM dwReserved, VTLPVOID pCallbackFunc, VTSYSPARAM dwCallbackData, VTLPHEXPORT phExport); From the header files I reduced the parameters to: typedef VTSYSPARAM VTHDOC, VTLPHDOC * typedef DWORD_PTR VTSYSPARAM typedef unsigned long DWORD_PTR typedef unsigned long VTDWORD typedef VTVOID* VTLPVOID #define VTVOID void typedef VTHDOC VTHEXPORT, *VTLPEXPORT These are for 32 bit windows Going through the header files, the example programs, and the documentation I found: 1. That pSpec could be a pointer to a buffer or NULL, so I set it to a IntPtr.Zero (documentation). 2. That dwFlags and dwReserved according to the documentation "Must be set by the developer to 0". 3. That pCallbackFunc can be set to NULL if I don't want to handle callbacks. 4. That the last two are based on structs that I wrote C# wrappers for using the [StructLayout(LayoutKind.Sequential)]. Then instatiated an instance and generated the parameters by first creating a IntPtr with Marshal.AllocHGlobal(Marshal.SizeOf(instance)), then getting the address value which is passed as a uint for dwCallbackData and a IntPtr for phExport. The final parameter list is as follows: 1. phDoc as a IntPtr which was loaded with an address by the DAOpenDocument function called before. 2. dwOutputId as uint set to 1535 which represents FI_JPEGFIF 3. dwSpecType as int set to 2 which represents IOTYPE_ANSIPATH 4. pSpec as an IntPtr.Zero where the output will be written 5. dwFlags as uint set to 0 as directed 6. dwReserved as uint set to 0 as directed 7. pCallbackFunc as IntPtr set to NULL as I will handle results 8. dwCallBackDate as uint the address of a buffer for a struct 9. phExport as IntPtr to another struct buffer still get an undefined error from the API. Meaning that the call returns a 961 which is not defined in any of the header files. In the past I have gotten this when my choice of parameter types are incorrect. I started out using Interop Assistant which was helpful in learning how many of the parameter types get translated. It is however limited by how well I am able to glean the correct native type from the header files. For example the hDoc parameter used in the preceding function was defined as a non-filesytem handle, so attempted to use Marshal to create a handle, then used an IntPtr, and finally it turned out to be an int (actually it was &phDoc used here). So is there a more scientific way of doing this, other than trial and error? Jim

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  • epoll_wait: maxevents

    - by someguy
    int epoll_wait(int epfd, struct epoll_event *events, int maxevents, int timeout); I'm a little confused about the maxevents parameter. Let's say I want to write a server that can handle up to 10k connections. Would I define maxevents as 10000 then, or should it be be lower for some reason?

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  • other way to add item to List<>

    - by netmajor
    In my other question You can see code of my arr structure and PriorityQueue collection. I normally add items to this collection like that: arr.PriorityQueue.Add(new element((value(item, endPoint) + value(startPoint, item)),item)); I am curious that is other way to do this (add element(which is struct) object to List) ? In lambda way for example ? I just eager for knowledge :)

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  • what is pagecache page

    - by kumar
    /* * Each physical page in the system has a struct page associated with * it to keep track of whatever it is we are using the page for at the * moment. Note that we have no way to track which tasks are using * a page, though if it is a pagecache page, rmap structures can tell us * who is mapping it. */ include/linux/mm_types.h Here Please lemme know what is "pagecache page" means? Thanks!

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  • C++ Unlocking a std::mutex before calling std::unique_lock wait

    - by Sant Kadog
    I have a multithreaded application (using std::thread) with a manager (class Tree) that executes some piece of code on different subtrees (embedded struct SubTree) in parallel. The basic idea is that each instance of SubTree has a deque that store objects. If the deque is empty, the thread waits until a new element is inserted in the deque or the termination criteria is reached. One subtree can generate objects and push them in the deque of another subtree. For convenience, all my std::mutex, std::locks and std::variable_condition are stored in a struct called "locks". The class Tree creates some threads that run the following method (first attempt) : void Tree::launch(SubTree & st, Locks & locks ) { /* some code */ std::lock_guard<std::mutex> deque_lock(locks.deque_mutex_[st.id_]) ; // lock the access to the deque of subtree st if (st.deque_.empty()) // check that the deque is still empty { // some threads are still running, wait for them to terminate std::unique_lock<std::mutex> wait_lock(locks.restart_mutex_[st.id_]) ; locks.restart_condition_[st.id_].wait(wait_lock) ; } /* some code */ } The problem is that "deque_lock" is still locked while the thread is waiting. Hence no object can be added in the deque of the current thread by a concurrent one. So I turned the lock_guard into a unique_lock and managed the lock/unlock manually : void launch(SubTree & st, Locks & locks ) { /* some code */ std::unique_lock<std::mutex> deque_lock(locks.deque_mutex_[st.id_]) ; // lock the access to the deque of subtree st if (st.deque_.empty()) // check that the deque is still empty { deque_lock.unlock() ; // unlock the access to the deque to enable the other threads to add objects // DATA RACE : nothing must happen to the unprotected deque here !!!!!! // some threads are still running, wait for them to terminate std::unique_lock<std::mutex> wait_lock(locks.restart_mutex_[st.id_]) ; locks.restart_condition_[st.id_].wait(wait_lock) ; } /* some code */ } The problem now, is that there is a data race, and I would like to make sure that the "wait" instruction is performed directly after the "deque_lock.unlock()" one. Would anyone know a way to create such a critical instruction sequence with the standard library ? Thanks in advance.

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  • Qt under Visual C++ 2010 Express

    - by Evil Spork
    I'm trying to build a basic Qt hello world inside visual studio. I got the moc step to work (i think), but I am at a loss as to how to pass this linker error.. 1>moc_mainwindow.obj : error LNK2001: unresolved external symbol "public: static struct QMetaObject const QMainWindow::staticMetaObject" (?staticMetaObject@QMainWindow@@2UQMetaObject@@B) I've pleanty of googling but I am really at a loss.

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  • how to bind a link local address to an ipv6 socket

    - by Haiyuan Zhang
    This thread can be treated as a sister thread of this. It's will be very tedious that when you want to bind a link local adress to a ipv6 socket you need to the set sin6_scope_id field of sockaddr_in6 struct as well. I'm wondering if someone can provide a good practise like solution here for me or anyone who interested in this topic to learn from.

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  • Inserting Records in Ascending Order function- C homework assignment

    - by Aaron McRuer
    Good day, Stack Overflow. I have a homework assignment that I'm working on this weekend that I'm having a bit of a problem with. We have a struct "Record" (which contains information about cars for a dealership) that gets placed in a particular spot in a linked list according to 1) its make and 2) according to its model year. This is done when initially building the list, when a "int insertRecordInAscendingOrder" function is called in Main. In "insertRecordInAscendingOrder", a third function, "createRecord" is called, where the linked list is created. The function then goes to the function "compareCars" to determine what elements get put where. Depending on the value returned by this function, insertRecordInAscendingOrder then places the record where it belongs. The list is then printed out. There's more to the assignment, but I'll cross that bridge when I come to it. Ideally, and for the assignment to be considered correct, the linked list must be ordered as: Chevrolet 2012 25 Chevrolet 2013 10 Ford 2010 5 Ford 2011 3 Ford 2012 15 Honda 2011 9 Honda 2012 3 Honda 2013 12 Toyota 2009 2 Toyota 2011 7 Toyota 2013 20 from the a text file that has the data ordered the following way: Ford 2012 15 Ford 2011 3 Ford 2010 5 Toyota 2011 7 Toyota 2012 20 Toyota 2009 2 Honda 2011 9 Honda 2012 3 Honda 2013 12 Chevrolet 2013 10 Chevrolet 2012 25 Notice that the alphabetical order of the "make" field takes precedence, then, the model year is arranged from oldest to newest. However, the program produces this as the final list: Chevrolet 2012 25 Chevrolet 2013 10 Honda 2011 9 Honda 2012 3 Honda 2013 12 Toyota 2009 2 Toyota 2011 7 Toyota 2012 20 Ford 2010 5 Ford 2011 3 Ford 2012 15 I sat down with a grad student and tried to work out all of this yesterday, but we just couldn't figure out why it was kicking the Ford nodes down to the end of the list. Here's the code. As you'll notice, I included a printList call at each instance of the insertion of a node. This way, you can see just what is happening when the nodes are being put in "order". It is in ANSI C99. All function calls must be made as they are specified, so unfortunately, there's no real way of getting around this problem by creating a more efficient algorithm. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LINE 50 #define MAX_MAKE 20 typedef struct record { char *make; int year; int stock; struct record *next; } Record; int compareCars(Record *car1, Record *car2); void printList(Record *head); Record* createRecord(char *make, int year, int stock); int insertRecordInAscendingOrder(Record **head, char *make, int year, int stock); int main(int argc, char **argv) { FILE *inFile = NULL; char line[MAX_LINE + 1]; char *make, *yearStr, *stockStr; int year, stock, len; Record* headRecord = NULL; /*Input and file diagnostics*/ if (argc!=2) { printf ("Filename not provided.\n"); return 1; } if((inFile=fopen(argv[1], "r"))==NULL) { printf("Can't open the file\n"); return 2; } /*obtain values for linked list*/ while (fgets(line, MAX_LINE, inFile)) { make = strtok(line, " "); yearStr = strtok(NULL, " "); stockStr = strtok(NULL, " "); year = atoi(yearStr); stock = atoi(stockStr); insertRecordInAscendingOrder(&headRecord,make, year, stock); } printf("The original list in ascending order: \n"); printList(headRecord); } /*use strcmp to compare two makes*/ int compareCars(Record *car1, Record *car2) { int compStrResult; compStrResult = strcmp(car1->make, car2->make); int compYearResult = 0; if(car1->year > car2->year) { compYearResult = 1; } else if(car1->year == car2->year) { compYearResult = 0; } else { compYearResult = -1; } if(compStrResult == 0 ) { if(compYearResult == 1) { return 1; } else if(compYearResult == -1) { return -1; } else { return compStrResult; } } else if(compStrResult == 1) { return 1; } else { return -1; } } int insertRecordInAscendingOrder(Record **head, char *make, int year, int stock) { Record *previous = *head; Record *newRecord = createRecord(make, year, stock); Record *current = *head; int compResult; if(*head == NULL) { *head = newRecord; printf("Head is null, list was empty\n"); printList(*head); return 1; } else if ( compareCars(newRecord, *head)==-1) { *head = newRecord; (*head)->next = current; printf("New record was less than the head, replacing\n"); printList(*head); return 1; } else { printf("standard case, searching and inserting\n"); previous = *head; while ( current != NULL &&(compareCars(newRecord, current)==1)) { printList(*head); previous = current; current = current->next; } printList(*head); previous->next = newRecord; previous->next->next = current; } return 1; } /*creates records from info passed in from main via insertRecordInAscendingOrder.*/ Record* createRecord(char *make, int year, int stock) { printf("CreateRecord\n"); Record *theRecord; int len; if(!make) { return NULL; } theRecord = malloc(sizeof(Record)); if(!theRecord) { printf("Unable to allocate memory for the structure.\n"); return NULL; } theRecord->year = year; theRecord->stock = stock; len = strlen(make); theRecord->make = malloc(len + 1); strncpy(theRecord->make, make, len); theRecord->make[len] = '\0'; theRecord->next=NULL; return theRecord; } /*prints list. lists print.*/ void printList(Record *head) { int i; int j = 50; Record *aRecord; aRecord = head; for(i = 0; i < j; i++) { printf("-"); } printf("\n"); printf("%20s%20s%10s\n", "Make", "Year", "Stock"); for(i = 0; i < j; i++) { printf("-"); } printf("\n"); while(aRecord != NULL) { printf("%20s%20d%10d\n", aRecord->make, aRecord->year, aRecord->stock); aRecord = aRecord->next; } printf("\n"); } The text file you'll need for a command line argument can be saved under any name you like; here are the contents you'll need: Ford 2012 15 Ford 2011 3 Ford 2010 5 Toyota 2011 7 Toyota 2012 20 Toyota 2009 2 Honda 2011 9 Honda 2012 3 Honda 2013 12 Chevrolet 2013 10 Chevrolet 2012 25 Thanks in advance for your help. I shall continue to plow away at it myself.

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