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• FOX toolkit, file concatentation

  - by Robb

  I'm using the FOX Toolkit and C++ to develop a GUI. I'm Having an issue with the FXFile::concat(...) command. The method looks like: FXFile::concat(const FXString & srcfile1, const FXString & srcfile2, const FXString & dstfile, FXbool overwrite = false And when I call it with the srcfile1 and dstfile being the same thing (because I need to simply add to srcfile1), the method does not work. dstfile is empty. Anyone have experience with FOX and this concatentation problem? I'm open to other suggestions as well, including boost.

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• C++ porting templates to Red hat enterprise linux version 5

  - by mkal

  #include <sys/stat.h> #include <sys/types.h> #include <unistd.h> template <class OutType> bool getVAL(OutType &value_out, const std::string &key) { return false; } int main (int argc, char*argv[]) { mode_t a; getVAL(a, "abc"); } test.cpp:6: error: ISO C++ forbids declaration of ‘parameter’ with no type test.cpp: In function ‘int main(int, char**)’: test.cpp:13: error: no matching function for call to ‘getVAL(mode_t&, const char [4])’

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• Accessing structure elements using pointers

  - by Arun Nadesh

  Hi Everybody, Greetings! I got surprised when the following program did not crash. typedef struct _x{ int a; char b; int c; }x; main() { x *ptr=0; char *d=&ptr->b; } As per my understanding the -> operator has higher precedence over & operator. So I expected the program to crash at the below statement when we try to dereference the NULL pointer tr. char *d=&ptr->b; But the statement &ptr->b evaluates to a valid address. Could somebody please explain where I'm wrong? Thanks & Regards, Arun

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• Hex to Decimal conversion in C

  - by darkie15

  Hi All, Here is my code which is doing the conversion from hex to decimal. The hex values are stored in a unsigned char array: int liIndex ; long hexToDec ; unsigned char length[4]; for (liIndex = 0; liIndex < 4 ; liIndex++) { length[liIndex]= (unsigned char) *content; printf("\n Hex value is %.2x", length[liIndex]); content++; } hexToDec = strtol(length, NULL, 16); Each array element contains 1 byte of information and I have read 4 bytes. When I execute it, here is the output that I get : Hex value is 00 Hex value is 00 Hex value is 00 Hex value is 01 Chunk length is 0 Can any one please help me understand the error here. Th decimal value should have come out as 1 instead of 0. Regards, darkie

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• Using an array in embedded x86 assembly??

  - by Mark V.

  Hey all I have a method (C++) that returns a character and takes an array of characters as its parameters. I'm messing with assembly for the first time and just trying to return the first character of the array in the dl register. Here's what I have so far: char returnFirstChar(char arrayOfLetters[]) { char max; __asm { push eax push ebx push ecx push edx mov dl, 0 mov eax, arrayOfLetters[0] xor edx, edx mov dl, al mov max, dl pop edx pop ecx pop ebx pop eax } return max; } For some reason this method returns a ? Any idea whats going on? Thanks

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• How to pass the structure to a function in C++ defined in another class?

  - by Dany

  I have a class Con as this:- class Con { public: struct MachineList { BSTR AccountId; BSTR MachineId; BSTR Make; char* Make1; BSTR Model; char* Model1; BSTR SerialNumber; BSTR IpAddress; char* IpAddress1; BSTR Port; int Port1; BSTR LocationCode; } machinelist[100] ; int w; } ; i created an object of Con class as Con m_con; I have another class Test class Test { public: void fun();//i want to pass the object of the structure that i created in Con //what arguments should i pass in fun function? };

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• C++ 'mutable' keyword

  - by Rob

  A while ago I came across some code that marked a member variable of a class with the 'mutable' keyword. As far as I can see it simply allows you to modify a variable in a 'const' method: class Foo { private: mutable bool done_; public: void doSomething() const { ...; done_ = true; } }; Is this the only use of this keyword or is there more to it than meets the eye? I have since used this technique in a class, marking a boost::mutex as mutable allowing const functions to lock it for thread-safety reasons, but, to be honest, it feels like a bit of a hack.

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• Embedding binary blobs using gcc mingw

  - by myforwik

  I am trying to embed binary blobs into an exe file. I am using mingw gcc. I make the object file like this: ld -r -b binary -o binary.o input.txt I then look objdump output to get the symbols: objdump -x binary.o And it gives symbols named: _binary_input_txt_start _binary_input_txt_end _binary_input_txt_size I then try and access them in my C program: #include <stdlib.h> #include <stdio.h> extern char _binary_input_txt_start[]; int main (int argc, char *argv[]) { char *p; p = _binary_input_txt_start; return 0; } Then I compile like this: gcc -o test.exe test.c binary.o But I always get: undefined reference to _binary_input_txt_start Does anyone know what I am doing wrong?

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• inserting std::strings in to a std::map

  - by PaulH

  I have a program that reads data from a file line-by-line. I would like to copy some substring of that line in to a map as below: std::map< DWORD, std::string > my_map; DWORD index; // populated with some data char buffer[ 1024 ]; // populated with some data char* element_begin; // points to some location in buffer char* element_end; // points to some location in buffer > element_begin my_map.insert( std::make_pair( index, std::string( element_begin, element_end ) ) ); This std::map<>::insert() operation takes a long time (It doubles the file parsing time). Is there a way to make this a less expensive operation? Thanks, PaulH

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• Converting from ANSI to Unicode

  - by Rayne

  Hi all, I'm using Visual Studio .NET 2003, and I'm trying to convert a program written in purely ANSI characters to be independent of Unicode/Multi-byte characters. The program has a callback function of pcap_loop, called "got_packet". It's defined as void got_packet(u_char *user, const struct pcap_pkthdr *header, const u_char *cpacket) { USES_CONVERSION; _TUCHAR *packet; packet = A2T(cpacket); ... } However, I get the error message error C2440: 'type cast': cannot convert from 'const u_char *' to 'ATL::CA2WEX<>' How do fix this? Thank you. Regards, Rayne

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• realloc()ing memory for a buffer used in recv()

  - by Hristo

  I need to recv() data from a socket and store it into a buffer, but I need to make sure get all of the data so I have things in a loop. So to makes sure I don't run out of room in my buffer, I'm trying to use realloc to resize the memory allocated to the buffer. So far I have: // receive response int i = 0; int amntRecvd = 0; char *pageContentBuffer = (char*) malloc(4096 * sizeof(char)); while ((amntRecvd = recv(proxySocketFD, pageContentBuffer + i, 4096, 0)) > 0) { i += amntRecvd; realloc(pageContentBuffer, 4096 + sizeof(pageContentBuffer)); } However, this doesn't seem to be working properly since Valgrind is complaining "valgrind: the 'impossible' happened:". Any advice as to how this should be done properly? Thanks, Hristo

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• Does printf have side effects?

  - by martani_net

  I have an array of the following strcuture struct T_info { char capitale[255]; char pays[255]; char commentaire[255]; }; struct T_info *tableau; Then when I populate the array and call printf allone on each element it works fine strcpy(tab[line].capitale, buffer); strcpy(tab[line].pays, buffer); strcpy(tab[line].commentaire, buffer); printf("%s\n", tab[line].capitale); printf("%s\n", tab[line].pays); printf("%s\n", tab[line].commentaire); but if I call, printf("%s, %s, %s", tab[line].capitale, tab[line].pays, tab[line].commentaires) I get wrong resutts, is printf changing its parameters or what is going on?

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• anagram!! problem with this code

  - by danielDhobbs

  hello people!! i have a problem with this code can you fix it for me? int anagram(char* word, int cur, int len){ int i, b = cur+1; char temp=0; char arrA[len]; printf("//%d**%d//", b, cur); for (i = 0 ; i < len ; i++) { arrA[i] = word[i]; } for (i = cur ; i < len ; i++) { if (b < len) { printf("%s\n", arrA); temp = arrA[cur]; arrA[cur] = arrA[b]; arrA[b] = temp; b++; } else if (b == len) anagram(arrA, b, len); } return 0; }

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• How to convert a unicode charactor array back to unicode sequence in C++

  - by eddyxd

  My problem is how to convert a c/c++ string/chractor array to another string contain the unicode(UTF-16) escape sequence of original one for example, I want to find a function F(char *ch) could do following function. char a[10] = "\u5f53"; printf("a = %s\n",a); char b[10]; b = F(a); //<- F is the function I wanted printf("b = %s\n",b); -------- console will show ------- a = ? b = \u5f53 Anyone has any Idea@@?~ thanks!! ps: I tried to guess \u5f35 means the value store in a, but it is not indeed the value of a[0] = -79 , a[1] = 105 ... So I don't know how to convert it back to the sequence of unicode.... Please give me a hane~ : )

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• Why isn't wchar_t widely used in code for Linux / related platforms?

  - by Ninefingers

  This intrigues me, so I'm going to ask - for what reason is wchar_t not used so widely on Linux/Linux-like systems as it is on Windows? Specifically, the Windows API uses wchar_t internally whereas I believe Linux does not and this is reflected in a number of open source packages using char types. My understanding is that given a character c which requires multiple bytes to represent it, then in a char[] form c is split over several parts of char* whereas it forms a single unit in wchar_t[]. Is it not easier, then, to use wchar_t always? Have I missed a technical reason that negates this difference? Or is it just an adoption problem?

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• Function Pointer from base class

  - by camelord

  Hi there, i need a Function Pointer from a base class. Here is the code: class CActionObjectBase { ... void AddResultStateErrorMessage( const char* pcMessage , ULONG iResultStateCode); ... } CActionObjectCalibration( ): CActionObjectBase() { ... m_Calibration = new CCalibration(&CActionObjectBase::AddResultStateErrorMessage); } class CCalibration { ... CCalibration(void (CActionObjectBase::* AddErrorMessage)(const char*, ULONG )); ... void (CActionObjectBase::* m_AddErrorMessage)(const char*, ULONG ); } Inside CCalibration in a Function occurs the Error. I try to call the Function Pointer like this: if(m_AddErrorMessage) { ... m_AddErrorMessage("bla bla", RSC_FILE_ERROR); } The Problem is, that I cannot compile. The Error Message says something like: error C2064: Expression is no Function, that takes two Arguments. What is wrong? regards camelord

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• Copy constructor demo (crashing... case 2)

  - by AKN

  Please have a glance at this program: class CopyCon { public: char *name; CopyCon() { name = new char[20]; name = "Hai";//_tcscpy(name,"Hai"); } CopyCon(const CopyCon &objCopyCon) { name = new char[_tcslen(objCopyCon.name)+1]; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete[] name; name = NULL; } } }; int main() { CopyCon obj1; CopyCon obj2(obj1); cout<<obj1.name<<endl; cout<<obj2.name<<endl; } This program crashes on execution. Error: "Expression: _BLOCK_TYPE_IS_VALID(pHead-nBlockUse)" If I assign "Hai" to name using aasignment operator, its crashing. Where as when I use string func _tcscpy to assign "Hai" to name, its working perfectly. Can some one explain why so?

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• A question for retrieve minix os version

  - by majnun

  Hi guys i'm having a project for the university in which (above others ) i have to get the minix os version from kernell call.I'm not a very experienced programmer so this is what i have come to (with some help ) int main (int argc, char *argv[] ) { char M3ca1[23]; message ml; m.m_u.m_m1.m3ca1= OS_VERSION; char temp=_syscall(MM,69,&m); printf("the os version is %c\n",temp); return 0; } and i get multiple errors.IF you have any ideas it would be greatly appreciated.

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• C++ overloading operator comma for variadic arguments

  - by uray

  is it possible to construct variadic arguments for function by overloading operator comma of the argument? i want to see an example how to do so.., maybe something like this: template <typename T> class ArgList { public: ArgList(const T& a); ArgList<T>& operator,(const T& a,const T& b); } //declaration void myFunction(ArgList<int> list); //in use: myFunction(1,2,3,4); //or maybe: myFunction(ArgList<int>(1),2,3,4);

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• Trying to understand strtok

  - by Karthick

  Consider the following snippet that uses strtok to split the string madddy. char* str = (char*) malloc(sizeof("Madddy")); strcpy(str,"Madddy"); char* tmp = strtok(str,"d"); std::cout<<tmp; do { std::cout<<tmp; tmp=strtok(NULL, "dddy"); }while(tmp!=NULL); It works fine, the output is Ma. But by modifying the strtok to the following, tmp=strtok(NULL, "ay"); The output becomes Madd. So how does strtok exactly work? I have this question because I expected strtok to take each and every character that is in the delimiter string to be taken as a delimiter. But in certain cases it is doing that way but in few cases, it is giving unexpected results. Could anyone help me understand this?

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• Question regarding inheritance in wxWidgets.

  - by celestialorb

  Currently I'm attempting to write my own wxObject, and I would like for the class to be based off of the wxTextCtrl class. Currently this is what I have: class CommandTextCtrl : public wxTextCtrl { public: void OnKey(wxKeyEvent& event); private: DECLARE_EVENT_TABLE() }; Then later on I have this line of code, which is doesn't like: CommandTextCtrl *ctrl = new CommandTextCtrl(panel, wxID_ANY, *placeholder, *origin, *size); ...and when I attempt to compile the program I receive this error: error: no matching function for call to ‘CommandTextCtrl::CommandTextCtrl(wxPanel*&, <anonymous enum>, const wxString&, const wxPoint&, const wxSize&)’ It seems that it doesn't inherit the constructor method with wxTextCtrl. Does anyone happen to know why it doesn't inherit the constructor? Thanks in advance for any help!

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• DB2 ZOS String Comparison Problem

  - by John

  I am comparing some CHAR data in a where clause in my sql like this, where PRI_CODE < PriCode The problem I am having is when the CHAR values are of different lengths. So if PRI_CODE = '0800' and PriCode = '20' it is returning true instead of false. It looks like it is comparing it like this '08' < '20' instead of like '0800' < '20' Does a CHAR comparison start from the Left until one or the other values end? If so how do I fix this? My values can have letters in it so convering to numeric is not an option.

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• Why is this default template parameter not allowed?

  - by Matt Joiner

  I have the following class: template <typename Type = void> class AlignedMemory { public: AlignedMemory(size_t alignment, size_t size) : memptr_(0) { int iret(posix_memalign((void **)&memptr_, alignment, size)); if (iret) throw system_error("posix_memalign"); } virtual ~AlignedMemory() { free(memptr_); } operator Type *() const { return memptr_; } Type *operator->() const { return memptr_; } //operator Type &() { return *memptr_; } //Type &operator[](size_t index) const; private: Type *memptr_; }; And attempt to instantiate an automatic variable like this: AlignedMemory blah(512, 512); This gives the following error: src/cpfs/entry.cpp:438: error: missing template arguments before ‘buf’ What am I doing wrong? Is void not an allowed default parameter?

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• Can a CWinApp be placed in a DLL?

  - by jmucchiello

  I'm updating some legacy apps to Visual Studio 10 and am in linker hell. All of these DLLs derive classes from CWinApp and use AfxGetApp() to get access to the object. When I link the DLLs I get unresolved externals that look like global static objects that would get pulled in by a normal app's main(): Shell.lib(SHELL.obj) : error LNK2001: unresolved external symbol "public: static struct CRuntimeClass const CException::classCException" (?classCException@CException@@2UCRuntimeClass@@B) Shell.lib(SHELL.obj) : error LNK2001: unresolved external symbol "public: static struct CRuntimeClass const CFrameWnd::classCFrameWnd" (?classCFrameWnd@CFrameWnd@@2UCRuntimeClass@@B) Shell.lib(SHELL.obj) : error LNK2001: unresolved external symbol "public: static class CRect const CFrameWnd::rectDefault" (?rectDefault@CFrameWnd@@2VCRect@@B) My current combination of ignore default libraries and additional libraries (the method you can easily google to find the answer to linker hell) is: msvcprtd.lib,mfc100d.lib,mfcs100d.lib,libcmtd.lib When I add nafxcwd.lib (the mfc library), these three external symbols resolve but I end up with a bunch of other duplicate symbols (requiring the use of /FORCE:MULTIPLE) and in end __argc and __argv become unresolved. So the basic question is: Can you link a DLL containing a CWinApp in VS10? How do you setup the linker to do it?

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• What does the '&' operator do in C++?

  - by rascher

  n00b question. I am a C guy and I'm trying to understand some C++ code. I have the following function declaration: int foo(const string &myname) { cout << "called foo for: " << myname << endl; return 0; } How does the function signature differ from the equivalent C: int foo(const char *myname) Is there a difference between using string *myname vs string &myname? What is the difference between & in C++ and * in C to indicate pointers? Similarly: const string &GetMethodName() { ... } What is the & doing here? Is there some website that explains how & is used differently in C vs C++?

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