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  • The question regarding cerr cout and clog

    - by skydoor
    Can anybody explain the difference between cerr cout and clog and why does different objects are proposed? I know the differences are as below: 1) cout can redirected but cerr can't 2) clog can use buffer. I am confused about the point 2, I am grateful if anybody can elaborate it more.

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  • How to return a string literal from a function

    - by skydoor
    Hi I am always confused about return a string literal or a string from a function. I was told that there might be memory leak because you don't know when the memory will be deleted? For example, in the code below, how to implement foo() so that make the output of the code is "Hello World"? void foo ( ) // you can add parameters here. { } int main () { char *c; foo ( ); printf ("%s",c); return 0; } Also if the return type of foo() is not void, but you can return char*, what should it be.

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  • Where is pure virtual function located in C++?

    - by skydoor
    Which virtual table will be pure virtual function located? In the base class or derived class? For example, what does the virtual table look like in each class? class Base { virtual void f() =0; virtual void g(); } class Derived: public Base{ virtual void f(); virtual void g(); }

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  • memset for initialization in C++

    - by skydoor
    memset is sometimes used to initialize data in a constructor like the example below. Does it work in general ? Is it a good idea in general? class A { public: A(); private: int a; float f; char str[35]; long *lp; }; A::A() { memset(this, 0, sizeof(*this)); }

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  • some qeustions about Vector in STL

    - by skydoor
    I have some questions about vector in STL to clarify..... 1 Where are the objects in vector allocated? heap? 2 does vector have boundary check? If the index out of the boundary, what error will happen? 3 Why array is faster than vector? 4 Is there any case in which vector is not applicable but array is a must?

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  • Why friend function is preferred to member function for operator<<

    - by skydoor
    When you are going to print an object, a friend operator<< is used. Can we use member function for operator<< ? class A { public: void operator<<(ostream& i) { i<<"Member function";} friend ostream& operator<<(ostream& i, A& a) { i<<"operator<<"; return i;} }; int main () { A a; A b; A c; cout<<a<<b<<c<<endl; a<<cout; return 0; } One point is that friend function enable us to use it like this cout<<a<<b<<c What other reasons?

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  • How to implement pure virtual function in C++

    - by skydoor
    Hi, I think the implementation of virtual function is talked about a lot. My question is what about pure virtual function? However it is implemented? In virtual table, how to tell it is a pure or non-pure? What the difference between pure virtual function and virtual function with implementation?

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  • How to debug a running C++ program in Linux?

    - by skydoor
    Hi I have a question about debugging a running C++ program in Linux. If a programming is already running and can't be interrupted, how to do that. I can find three ways, but I don't know too much about details, I am grateful if any one can elaborate it deeper. 1) we can use GDB by specifying the process ID gdb -p PID In this case, what's the difference between this and attach PID? 2) We can use pstat, however, I am using Ubuntu, no pstat, but only mpstat it seems that mpstat does not provide too much information, and not so many options. 3) check the details information under directory ./proc In this case, just go to the directory with the PID. However, should this be done mannually?

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  • How could one emulate namespace in C?

    - by skydoor
    In C++ one might use namespace to keep independent groups working in the same code base from inadvertently creating functions with the same name and thus creating a conflict. My question is, before the idea of namespace comes out, how might one emulate namespace in C.

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  • Singleton pattern in C++

    - by skydoor
    I have a question about the singleton pattern. I saw two cases concerning the static member in the singleton class. First it is an object, like this class CMySingleton { public: static CMySingleton& Instance() { static CMySingleton singleton; return singleton; } // Other non-static member functions private: CMySingleton() {} // Private constructor ~CMySingleton() {} CMySingleton(const CMySingleton&); // Prevent copy-construction CMySingleton& operator=(const CMySingleton&); // Prevent assignment }; One is an pointer, like this class GlobalClass { int m_value; static GlobalClass *s_instance; GlobalClass(int v = 0) { m_value = v; } public: int get_value() { return m_value; } void set_value(int v) { m_value = v; } static GlobalClass *instance() { if (!s_instance) s_instance = new GlobalClass; return s_instance; } }; What's the difference between the two cases? Which one is correct?

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  • What's the outcome if I use free with new or delete with malloc?

    - by skydoor
    It is a compiler error or runtime error? The code below can be compiled! class Base{ void g(); void h(); }; int main() { Base* p = new Base(); free(p); return 0; } However it can't be compiled with a virtual function if I declare the class Base like this class Base{ virtual void g(); void h(); }; The code below can be compiled all the time, no matter the function is virtual or not. class Base{ void g(); void h(); }; int main() { Base* p = (Base*)malloc(sizeof(Base)); delete p; return 0; }

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