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Search found 59 results on 3 pages for 'lvalue'.

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• pointer, malloc and char in C

  - by user2534078

  im trying to copy a const char array to some place in the memory and point to it . lets say im defining this var under the main prog : char *p = NULL; and sending it to a function with a string : myFunc(&p, "Hello"); now i want that at the end of this function the pointer will point to the letter H but if i puts() it, it will print Hello . here is what i tried to do : void myFunc(char** ptr , const char strng[] ) { *ptr=(char *) malloc(sizeof(strng)); char * tmp=*ptr; int i=0; while (1) { *ptr[i]=strng[i]; if (strng[i]=='\0') break; i++; } *ptr=tmp; } i know its a rubbish now, but i would like to understand how to do it right, my idea was to allocate the needed memory, copy a char and move forward with the pointer, etc.. also i tried to make the ptr argument byreferenec (like &ptr) but with no success due to a problem with the lvalue and rvalue . the only thing is changeable for me is the function, and i would like not to use strings, but chars as this is and exercise . thanks for any help in advance.

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• I can't compile this code

  - by heshim

  #include <stdio.h> #define IN 1 /* inside a word */ #define OUT 0 /* outside a word */ /* count lines, words, and characters in input */ main() { int c, nl, nw, nc, state; state = OUT; nl = nw = nc = 0; while ((c = getchar()) != EOF) { ++nc; if (c == '\n') ++nl; if (c == ' ' || c == '\n' || c = '\t') state = OUT; else if (state == OUT) { state = IN; ++nw; } } printf("%d %d %d\n", nl, nw, nc); } I got K&R book but there are some codes that don't compile ! it gives me - 19 C:\Users\Nom\Desktop\Untitled1.c invalid lvalue in assignment edit: now it works, thanks guys, but now it does nothing ! the printf statement doesn't work. It opens the dos console, I type anything and it just return a new line. I'm using Dev-C++ 4.9.9.2 I put the printf statement inside the while loop and it works now. thanks

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• Yesterday's broken codebase hunt me back

  - by sandun dhammika

  I need a fun oky. I just love this openmoko hardware and hacking into it. Please could somebody help me to compile qemu.I 'm so sad and I want to compile qemu and it required the GCC3.x and then I downloaded gcc 3.2 but when I configure it and build it, it gives a very sad error message. G_FOR_TARGET=" "SHELL=/bin/sh" "EXPECT=expect" "RUNTEST=runtest" "RUNTESTFLAGS=" "exec_prefix=/gcc-3.2" "infodir=/gcc-3.2/info" "libdir=/gcc-3.2/lib" "prefix=/gcc-3.2" "tooldir=/gcc-3.2/i686-pc-linux-gnu" "AR=ar" "AS=as" "CC=gcc" "CXX=c++" "LD=ld" "LIBCFLAGS=-g -O2" "NM=nm" "PICFLAG=" "RANLIB=ranlib" "DESTDIR=" DO=all multi-do make[1]: Leaving directory `/gcc-3.2/gcc-3.2/zlib' make[1]: Entering directory `/gcc-3.2/gcc-3.2/fastjar' make[1]: Leaving directory `/gcc-3.2/gcc-3.2/fastjar' make[1]: Entering directory `/gcc-3.2/gcc-3.2/gcc' gcc -c -DIN_GCC -g -O2 -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wtraditional -pedantic -Wno-long-long -DHAVE_CONFIG_H -DGENERATOR_FILE -I. -I. -I. -I./. -I./config -I./../include ./read-rtl.c -o read-rtl.o In file included from ./read-rtl.c:24:0: ./rtl.h:125:3: warning: type of bit-field ‘code’ is a GCC extension ./rtl.h:128:3: warning: type of bit-field ‘mode’ is a GCC extension ./read-rtl.c: In function ‘fatal_with_file_and_line’: ./read-rtl.c:61:1: warning: traditional C rejects ISO C style function definitions ./read-rtl.c: In function ‘read_rtx’: ./read-rtl.c:662:8: error: lvalue required as increment operand make[1]: *** [read-rtl.o] Error 1 make[1]: Leaving directory `/gcc-3.2/gcc-3.2/gcc' make: *** [all-gcc] Error 2 This is so sad and this is sooo bad. I have searched patches and workaround all over the Internet to this,but I couldn't find any alternative for this. I'm out of my patience now. I want that virtual machine ready and I want to make a debug host cos I don't have some money to buy original neo 1937 hardware. The patch that I have found comes with a nasty error too. I'm so sick of it.Any idea how could I fix this problem and make this work? Please please I'm begging you somebody help me please. Thanks all.

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• Specializating a template function that takes a universal reference parameter

  - by David Stone

  How do I specialize a template function that takes a universal reference parameter? foo.hpp: template<typename T> void foo(T && t) // universal reference parameter foo.cpp template<> void foo<Class>(Class && class) { // do something complicated } Here, Class is no longer a deduced type and thus is Class exactly; it cannot possibly be Class &, so reference collapsing rules will not help me here. I could perhaps create another specialization that takes a Class & parameter (I'm not sure), but that implies duplicating all of the code contained within foo for every possible combination of rvalue / lvalue references for all parameters, which is what universal references are supposed to avoid. Is there some way to accomplish this? To be more specific about my problem in case there is a better way to solve it: I have a program that can connect to multiple game servers, and each server, for the most part, calls everything by the same name. However, they have slightly different versions for a few things. There are a few different categories that these things can be: a move, an item, etc. I have written a generic sort of "move string to move enum" set of functions for internal code to call, and my server interface code has similar functions. However, some servers have their own internal ID that they communicate with, some use strings, and some use both in different situations. Now what I want to do is make this a little more generic. I want to be able to call something like ServerNamespace::server_cast<Destination>(source). This would allow me to cast from a Move to a std::string or ServerMoveID. Internally, I may need to make a copy (or move from) because some servers require that I keep a history of messages sent. Universal references seem to be the obvious solution to this problem. The header file I'm thinking of right now would expose simply this: namespace ServerNamespace { template<typename Destination, typename Source> Destination server_cast(Source && source); } And the implementation file would define all legal conversions as template specializations.

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• How to reduce redundant code when adding new c++0x rvalue reference operator overloads

  - by Inverse

  I am adding new operator overloads to take advantage of c++0x rvalue references, and I feel like I'm producing a lot of redundant code. I have a class, tree, that holds a tree of algebraic operations on double values. Here is an example use case: tree x = 1.23; tree y = 8.19; tree z = (x + y)/67.31 - 3.15*y; ... std::cout << z; // prints "(1.23 + 8.19)/67.31 - 3.15*8.19" For each binary operation (like plus), each side can be either an lvalue tree, rvalue tree, or double. This results in 8 overloads for each binary operation: // core rvalue overloads for plus: tree operator +(const tree& a, const tree& b); tree operator +(const tree& a, tree&& b); tree operator +(tree&& a, const tree& b); tree operator +(tree&& a, tree&& b); // cast and forward cases: tree operator +(const tree& a, double b) { return a + tree(b); } tree operator +(double a, const tree& b) { return tree(a) + b; } tree operator +(tree&& a, double b) { return std::move(a) + tree(b); } tree operator +(double a, tree&& b) { return tree(a) + std::move(b); } // 8 more overloads for minus // 8 more overloads for multiply // 8 more overloads for divide // etc which also has to be repeated in a way for each binary operation (minus, multiply, divide, etc). As you can see, there are really only 4 functions I actually need to write; the other 4 can cast and forward to the core cases. Do you have any suggestions for reducing the size of this code? PS: The class is actually more complex than just a tree of doubles. Reducing copies does dramatically improve performance of my project. So, the rvalue overloads are worthwhile for me, even with the extra code. I have a suspicion that there might be a way to template away the "cast and forward" cases above, but I can't seem to think of anything.

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• Why does virtual assignment behave differently than other virtual functions of the same signature?

  - by David Rodríguez - dribeas

  While playing with implementing a virtual assignment operator I have ended with a funny behavior. It is not a compiler glitch, since g++ 4.1, 4.3 and VS 2005 share the same behavior. Basically, the virtual operator= behaves differently than any other virtual function with respect to the code that is actually being executed. struct Base { virtual Base& f( Base const & ) { std::cout << "Base::f(Base const &)" << std::endl; return *this; } virtual Base& operator=( Base const & ) { std::cout << "Base::operator=(Base const &)" << std::endl; return *this; } }; struct Derived : public Base { virtual Base& f( Base const & ) { std::cout << "Derived::f(Base const &)" << std::endl; return *this; } virtual Base& operator=( Base const & ) { std::cout << "Derived::operator=( Base const & )" << std::endl; return *this; } }; int main() { Derived a, b; a.f( b ); // [0] outputs: Derived::f(Base const &) (expected result) a = b; // [1] outputs: Base::operator=(Base const &) Base & ba = a; Base & bb = b; ba = bb; // [2] outputs: Derived::operator=(Base const &) Derived & da = a; Derived & db = b; da = db; // [3] outputs: Base::operator=(Base const &) ba = da; // [4] outputs: Derived::operator=(Base const &) da = ba; // [5] outputs: Derived::operator=(Base const &) } The effect is that the virtual operator= has a different behavior than any other virtual function with the same signature ([0] compared to [1]), by calling the Base version of the operator when called through real Derived objects ([1]) or Derived references ([3]) while it does perform as a regular virtual function when called through Base references ([2]), or when either the lvalue or rvalue are Base references and the other a Derived reference ([4],[5]). Is there any sensible explanation to this odd behavior?

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• map<string, vector<string>> reassignment of vector value

  - by user2950936

  I am trying to write a program that takes lines from an input file, sorts the lines into 'signatures' for the purpose of combining all words that are anagrams of each other. I have to use a map, storing the 'signatures' as the keys and storing all words that match those signatures into a vector of strings. Afterwards I must print all words that are anagrams of each other on the same line. Here is what I have so far: #include <iostream> #include <string> #include <algorithm> #include <map> #include <fstream> using namespace std; string signature(const string&); void printMap(const map<string, vector<string>>&); int main(){ string w1,sig1; vector<string> data; map<string, vector<string>> anagrams; map<string, vector<string>>::iterator it; ifstream myfile; myfile.open("words.txt"); while(getline(myfile, w1)) { sig1=signature(w1); anagrams[sig1]=data.push_back(w1); //to my understanding this should always work, } //either by inserting a new element/key or //by pushing back the new word into the vector<string> data //variable at index sig1, being told that the assignment operator //cannot be used in this way with these data types myfile.close(); printMap(anagrams); return 0; } string signature(const string& w) { string sig; sig=sort(w.begin(), w.end()); return sig; } void printMap(const map& m) { for(string s : m) { for(int i=0;i<m->second.size();i++) cout << m->second.at(); cout << endl; } } The first explanation is working, didn't know it was that simple! However now my print function is giving me: prob2.cc: In function âvoid printMap(const std::map<std::basic_string<char>, std::vector<std::basic_string<char> > >&)â: prob2.cc:43:36: error: cannot bind âstd::basic_ostream<char>::__ostream_type {aka std::basic_ostream<char>}â lvalue to âstd::basic_ostream<char>&&â In file included from /opt/centos/devtoolset-1.1/root/usr/lib/gcc/x86_64-redhat-linux/4.7.2/../../../../include/c++/4.7.2/iostream:40:0, Tried many variations and they always complain about binding void printMap(const map<string, vector<string>> &mymap) { for(auto &c : mymap) cout << c.first << endl << c.second << endl; }

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• Undefined reference to vtable

  - by RyanG

  So, I'm getting the infamously horrible "undefined reference to 'vtable..." error for the following code (The class in question is CGameModule.) and I cannot for the life of me understand what the problem is. At first, I thought it was related to forgetting to give a virtual function a body, but as far as I understand, everything is all here. The inheritance chain is a little long, but here is the related source code. I'm not sure what other information I should provide. My code: class CGameModule : public CDasherModule { public: CGameModule(Dasher::CEventHandler *pEventHandler, CSettingsStore *pSettingsStore, CDasherInterfaceBase *pInterface, ModuleID_t iID, const char *szName) : CDasherModule(pEventHandler, pSettingsStore, iID, 0, szName) { g_pLogger->Log("Inside game module constructor"); m_pInterface = pInterface; } virtual ~CGameModule() {}; std::string GetTypedTarget(); std::string GetUntypedTarget(); bool DecorateView(CDasherView *pView) { //g_pLogger->Log("Decorating the view"); return false; } void SetDasherModel(CDasherModel *pModel) { m_pModel = pModel; } virtual void HandleEvent(Dasher::CEvent *pEvent); private: CDasherNode *pLastTypedNode; CDasherNode *pNextTargetNode; std::string m_sTargetString; size_t m_stCurrentStringPos; CDasherModel *m_pModel; CDasherInterfaceBase *m_pInterface; }; } Inherits from... class CDasherModule; typedef std::vector<CDasherModule*>::size_type ModuleID_t; /// \ingroup Core /// @{ class CDasherModule : public Dasher::CDasherComponent { public: CDasherModule(Dasher::CEventHandler * pEventHandler, CSettingsStore * pSettingsStore, ModuleID_t iID, int iType, const char *szName); virtual ModuleID_t GetID(); virtual void SetID(ModuleID_t); virtual int GetType(); virtual const char *GetName(); virtual bool GetSettings(SModuleSettings **pSettings, int *iCount) { return false; }; private: ModuleID_t m_iID; int m_iType; const char *m_szName; }; Which inherits from.... namespace Dasher { class CEvent; class CEventHandler; class CDasherComponent; }; /// \ingroup Core /// @{ class Dasher::CDasherComponent { public: CDasherComponent(Dasher::CEventHandler* pEventHandler, CSettingsStore* pSettingsStore); virtual ~CDasherComponent(); void InsertEvent(Dasher::CEvent * pEvent); virtual void HandleEvent(Dasher::CEvent * pEvent) {}; bool GetBoolParameter(int iParameter) const; void SetBoolParameter(int iParameter, bool bValue) const; long GetLongParameter(int iParameter) const; void SetLongParameter(int iParameter, long lValue) const; std::string GetStringParameter(int iParameter) const; void SetStringParameter(int iParameter, const std::string & sValue) const; ParameterType GetParameterType(int iParameter) const; std::string GetParameterName(int iParameter) const; protected: Dasher::CEventHandler *m_pEventHandler; CSettingsStore *m_pSettingsStore; }; /// @} #endif

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• Binary operator overloading on a templated class (C++)

  - by GRB

  Hi all, I was recently trying to gauge my operator overloading/template abilities and as a small test, created the Container class below. While this code compiles fine and works correctly under MSVC 2008 (displays 11), both MinGW/GCC and Comeau choke on the operator+ overload. As I trust them more than MSVC, I'm trying to figure out what I'm doing wrong. Here is the code: #include <iostream> using namespace std; template <typename T> class Container { friend Container<T> operator+ <> (Container<T>& lhs, Container<T>& rhs); public: void setobj(T ob); T getobj(); private: T obj; }; template <typename T> void Container<T>::setobj(T ob) { obj = ob; } template <typename T> T Container<T>::getobj() { return obj; } template <typename T> Container<T> operator+ <> (Container<T>& lhs, Container<T>& rhs) { Container<T> temp; temp.obj = lhs.obj + rhs.obj; return temp; } int main() { Container<int> a, b; a.setobj(5); b.setobj(6); Container<int> c = a + b; cout << c.getobj() << endl; return 0; } This is the error Comeau gives: Comeau C/C++ 4.3.10.1 (Oct 6 2008 11:28:09) for ONLINE_EVALUATION_BETA2 Copyright 1988-2008 Comeau Computing. All rights reserved. MODE:strict errors C++ C++0x_extensions "ComeauTest.c", line 27: error: an explicit template argument list is not allowed on this declaration Container<T> operator+ <> (Container<T>& lhs, Container<T>& rhs) ^ 1 error detected in the compilation of "ComeauTest.c". I'm having a hard time trying to get Comeau/MingGW to play ball, so that's where I turn to you guys. It's been a long time since my brain has melted this much under the weight of C++ syntax, so I feel a little embarrassed ;). Thanks in advance. EDIT: Eliminated an (irrelevant) lvalue error listed in initial Comeau dump.

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