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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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• 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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• 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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• 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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• 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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• 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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• Variadic functions and arguments assignment in C/C++

  - by Rizo

  I was wondering if in C/C++ language it is possible to pass arguments to function in key-value form. For example in python you can do: def some_function(arg0 = "default_value", arg1): # (...) value1 = "passed_value" some_function(arg1 = value1) So the alternative code in C could look like this: void some_function(char *arg0 = "default_value", char *arg1) { ; } int main() { char *value1 = "passed_value"; some_function(arg1 = value1); return(0); } So the arguments to use in some_function would be: arg0 = "default_value" arg1 = "passed_value" Any ideas?

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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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• 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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• 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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• Loading an OverlayView from XIB -vs- programmatically for use with UIImagePickerController

  - by PLG

  I am currently making a camera app for iPhone and I have a strange phenomenon that I can't figure out. I would appreciate some help understanding. When recreating an overlay view for passing to UIImagePickerController, I have been successfully been able to create the view programmatically. What I haven't been able to do is create the view with/without controller in IB, load it and pass it to the overlay pointer successfully. If I do it via IB, the view is not opaque and obscures the view of the camera completely. I can not figure out why. I was thinking that the normal view pointer might be assigned when loading from XIB and therefore overwrite the camera's view, but I have an example programmatically where view and overlayView are set equal in the controller class. Perhaps the load order is overwriting a pointer? Help would be appreciated... kind regards.

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• Why does this code read all ' ' for the anything after the 4th character?

  - by djs22

  #define fileSize 100000 int main(int argc, char *argv[]){ char *name=argv[1]; char ret[fileSize]; FILE *fl = fopen(name, "rb"); fseek(fl, 0, SEEK_END); long len = fileSize; fseek(fl, 0, SEEK_SET); //fread(ret, 1, len, fl); int i; *(ret+fileSize) = '\0'; for (i=0; i<fileSize; i++){ *(ret+i)=fgetc(fl); printf("byte : %s \n", ret); } fclose(fl); } In the above code, when I feed the name of a jpeg file, it reads anything after the 4th character as ' '...any ideas? Thanks!

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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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• C#: What is the preferred way to handle this error?

  - by Ash

  I have a class 'Hand' that consists of two playing cards as below: public class Card { public char r, s; public Card(char rank, char suit) { r = rank; s = suit; } } public class Hand { public Card c1, c2; public Hand(Card one, Card two) { c1 = one; c2 = two; } } In a 52 card deck we can't have two identical cards. How should I deal with an error where I accidentally instance a class with two identical cards, e.g (Ah, Ah)? Thanks, Ash

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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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• how to read character from console in c++?

  - by tsubasa

  I'm struggling with reading characters from console in c++. Here is what I tried to do: char x; char y; char z; cout<<"Please enter your string: "; string s; getline(cin,s); istringstream is(s); is>> x >> y >> z; The problem is if the user enter something like this "1 20 100": x will get 1 y will get 2 z will get 0 What I want to get is x = 1; y = 20; z = 100; Anybody has suggestions?

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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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• Unresolved symbol when inheriting interface

  - by LeopardSkinPillBoxHat

  It's late at night here and I'm going crazy trying to solve a linker error. If I have the following abstract interface: class IArpPacketBuilder { public: IArpPacketBuilder(const DslPortId& aPortId); virtual ~IArpPacketBuilder(); // Other abstract (pure virtual methods) here... }; and I instantiate it like this: class DummyArpPacketBuilder : public IArpPacketBuilder { public: DummyArpPacketBuilder(const DslPortId& aPortId) : IArpPacketBuilder(aPortId) {} ~DummyArpPacketBuilder() {} }; why am I getting the following error when linking? Unresolved symbol references: IArpPacketBuilder::IArpPacketBuilder(DslPortId const&): ppc603_vxworks/_arpPacketQueue.o IArpPacketBuilder::~IArpPacketBuilder(): ppc603_vxworks/_arpPacketQueue.o typeinfo for IArpPacketBuilder: ppc603_vxworks/_arpPacketQueue.o *** Error code 1 IArpPacketBuilder is an abstract interface, so as long as I define the constructors and destructions in the concrete (derived) interface, I should be fine, no? Well it appears not.

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• Default values on arguments in C functions and function overloading in C

  - by inquam

  Converting a C++ lib to ANSI C and it seems like though ANSI C doesn't support default values for function variables or am I mistaken? What I want is something like int funcName(int foo, bar* = NULL); Also, is function overloading possible in ANSI C? Would need const char* foo_property(foo_t* /* this */, int /* property_number*/); const char* foo_property(foo_t* /* this */, const char* /* key */, int /* iter */); Could of course just name them differently but being used to C++ I kinda used to function overloading.

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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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• string manipulation without alloc mem in c

  - by Mike

  I'm wondering if there is another way of getting a sub string without allocating memory. To be more specific, I have a string as: const char *str = "9|0\" 940 Hello"; Currently I'm getting the 940, which is the sub-string I want as, char *a = strstr(str,"9|0\" "); char *b = substr(a+5, 0, 3); // gives me the 940 Where substr is my sub string procedure. The thing is that I don't want to allocate memory for this by calling the sub string procedure. Is there a much easier way?, perhaps by doing some string manipulation and not alloc mem. I'll appreciate any feedback.

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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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• What causes my borderless C++/CLI app to crash when overriding WndProc?

  - by Ste

  I use a form with border NONE. I need to override WndProc for resize and move form. However, using this code, my app crashes! static const int WM_NCHITTEST = 0x0084; static const int HTCLIENT = 1; static const int HTCAPTION = 2; protected: virtual void Form1::WndProc(System::Windows::Forms::Message %m) override { switch (m.Msg) { case WM_NCHITTEST: if (m.Result == IntPtr(HTCLIENT)) { m.Result = IntPtr(HTCAPTION); } break; } Form1::WndProc(m); } virtual System::Windows::Forms::CreateParams^ get() override { System::Windows::Forms::CreateParams^ cp = __super::CreateParams; cp->Style |= 0x40000; return cp; } How can I fix my code not to crash but still allow my form to be moved and resized?

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• Data Types and Structs

  - by dubya

  I'm reviewing for a test, and I am stumped by this question. Consider the following declarations: enum CategoryType {HUMANITIES, SOCIALSCIENCE, NATURALSCIENCE}; const int NUMCOURSES = 100; struct CourseRec { string courseName; int courseNum; CategoryType courseCategory; }; typedef CourseRec CourseList [NUMCOURSES]; CourseList courses; int index1, index2; What is the data type of the expression courses[index1] .courseName[index2] ? (a) CourseList (b) CourseRec (c) string (d) char (e) none; the expression is syntactically invalid I thought that the answer would be string, since courseName is a string, or maybe even CourseRec, since it is in the struct, but the answer is (d)char. Why is this a char data type? Any help is greatly appreciated.

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• gdb: SIGTRAP on std::string::c_str() call

  - by sheepsimulator

  So I've been trying to use gdb to return the value of a string I have by calling > print <member variable name>.c_str() But everytime I do so, I get this: Program received signal SIGTRAP, Trace/breakpoint trap. <some address> in std::string::c_str() from /usr/lib/libstdc++.so.6 GDB remains in the frame where the signal was received. To change this behavior use "set unwindonsignal on" Evaluation of the expression containing the function (std::string::c_str() const) will be abandoned. Two questions: Why/how is the standard library throwing SIGTRAP? I checked basic_string.h and c_str() is defined as: const _CharT* c_str() const { return _M_data(); } I don't see any SIGTRAP-throwing here... is there a way to get around this SIGTRAP? How can I read the text value of the std::string out (without getting some crazy extension library) in gdb?

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