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  • operator new for array of class without default constructor......

    - by skydoor
    For a class without default constructor, operator new and placement new can be used to declare an array of such class. When I read the code in More Effective C++, I found the code as below(I modified some part)..... My question is, why [] after the operator new is needed? I test it without it, it still works. Can any body explain that? class A { public: int i; A(int i):i(i) {} }; int main() { void *rawMemory = operator new[] (10 * sizeof(A)); // Why [] needed here? A *p = static_cast<A*>(rawMemory); for(int i = 0 ; i < 10 ; i++ ) { new(&p[i])A(i); } for(int i = 0 ; i < 10 ; i++ ) { cout<<p[i].i<<endl; } for(int i = 0 ; i < 10 ; i++ ) { p[i].~A(); } return 0; }

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  • question about sorting

    - by skydoor
    Bubble sort is O(n) at best, O(n^2) at worst, and its memory usage is O(1) . Merge sort is always O(n log n), but its memory usage is O(n). Which algorithm we would use to implement a function that takes an array of integers and returns the max integer in the collection, assuming that the length of the array is less than 1000. What if the array length is greater than 1000?

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  • Why friend overloaded operator is preferred to conversion operator in this case

    - by skydoor
    Hi I have a code like this, I think both the friend overloaded operator and conversion operator have the similar function. However, why does the friend overloaded operator is called in this case? What's the rules? Thanks so much! class A{ double i; public: A(int i):i(i) {} operator double () const { cout<<"conversion operator"<<endl;return i;} // a conversion operator friend bool operator>(int i, A a); // a friend funcion of operator > }; bool operator>(int i, A a ){ cout<<"Friend"<<endl; return i>a.i; } int main() { A aa(1); if (0 > aa){ return 1; } }

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  • Factory, Abstract Factory and Factory Method

    - by skydoor
    Hi, I am really confused about these three terms. My understanding is that: in the Factory pattern, there is no concrete factory. The factory builds the new objects according to the parameters. in Abstract Factory pattern, there are multiple concrete factories. The client has to create different concrete factories explicitly. Is that right? What are the other differences? Furthermore, what is the Factory Method pattern? Is it same as the Factory pattern?

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  • What are shared by multi threads in the same process?

    - by skydoor
    I found that each thread still has its own registers. Also has its own stack, but other threads can read and write the stack memory. My questions, what are shared by the multi threads in the same process? What I can imagine is 1) address space of the process; 2) stack, register; 3) variables Can any body elaborate it and add more?

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  • Some questions about Vector in STL

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

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  • why pointer to pointer is needed to allocate memory in function

    - by skydoor
    Hi I have a segmentation fault in the code below, but after I changed it to pointer to pointer, it is fine. Could anybody give me any reason? void memory(int * p, int size) { try{ p = (int *) malloc(size*sizeof(int)); } catch( exception& e) { cout<<e.what()<<endl; } } it does not work in the main function as blow int *p = 0; memory(p, 10); for(int i = 0 ; i < 10; i++) p[i] = i; however, it works like this . void memory(int ** p, int size) { `//pointer to pointer` try{ *p = (int *) malloc(size*sizeof(int)); } catch( exception& e) { cout<<e.what()<<endl; } } int main() { int *p = 0; memory(&p, 10); //get the address of the pointer for(int i = 0 ; i < 10; i++) p[i] = i; for(int i = 0 ; i < 10; i++) cout<<*(p+i)<<" "; return 0; }

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  • volatile vs. mutable in C++

    - by skydoor
    Hi I have a question about the difference between volatile and mutable. I noticed that both of the two means that it could be changed. What else? Are they the same thing? What's the difference? Where are they applicable? Why the two ideas are proposed? How to use them in different way? Thanks a lot.

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  • How default assignment operator works in struct?

    - by skydoor
    Suppose I have a structure in C++ containing a name and a number, e.g. struct person { char name[20]; int ssn; }; Suppose I declare two person variables: person a; person b; where a.name = "George", a.ssn = 1, and b.name = "Fred" and b.ssn = 2. Suppose later in the code a = b; printf("%s %d\n",a.name, a.ssn);

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  • How to make this code compile?

    - by skydoor
    // File: foo.c static int var; void foo() { var++; } // end of file foo.c // File bar.c: static int var; void bar() { var++; } // end of file bar.c // file main.c static int var; void main() { foo(); bar(); printf("%d", var); } // end of file main.c Question: Will the above program compile ? If so what will be the result ? I tested the code and found it couldn't be compiled. I try to use extern in main.c to use the function foo() and bar() but it still couldn't be compiled.

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