initialization

问题 i ran into a segfault running the following program #include <iostream> #include <vector> template <typename Derived> struct CRTPBase { CRTPBase() { func(); } void func() { static_cast<Derived*>(this)->_func(); } }; struct CRTPChild : CRTPBase<CRTPChild>{ using CRTPBase<CRTPChild>::CRTPBase; void _func(){ vec.resize(10); vec[0] = 2; } std::vector<int> vec; }; int main() { CRTPChild obj; std::cout << obj.vec[0] << std::endl; } When i replace vec with a member of type int it doesn't segfault

问题 i ran into a segfault running the following program #include <iostream> #include <vector> template <typename Derived> struct CRTPBase { CRTPBase() { func(); } void func() { static_cast<Derived*>(this)->_func(); } }; struct CRTPChild : CRTPBase<CRTPChild>{ using CRTPBase<CRTPChild>::CRTPBase; void _func(){ vec.resize(10); vec[0] = 2; } std::vector<int> vec; }; int main() { CRTPChild obj; std::cout << obj.vec[0] << std::endl; } When i replace vec with a member of type int it doesn't segfault

问题 An interesting question arose as a side effect of some other question here, about the possible differences between how C and C++ handle (the non-static-storage-duration): int arr[7] = {0}; Someone was stating that, in C++, the other elements were not guaranteed to be zero but I'm not sure I agree. Now C11 states, in 6.7.9 Initialization /19 : The initialization shall occur in initializer list order, each initializer provided for a particular subobject overriding any previously listed

问题 I'm currently having trouble with part of Chapter 6 of "Programming: Principles and Practice Using C++" (2nd ed, 3rd printing). According to the book's index, an example of a member initializer list is on page 184. Part of page 184 reads as follows: "Here, we'll just provide two member functions to give us a more convenient way of initializing Tokens: class Token { public: char kind; // what kind of token double value; // for numbers: a value }; We can now initialize ("construct") Token

问题 Why in super() keyword, can we omit self ? What if we don't omit it? class A: def __init__(self, var1, var2): """ some code """ class B(A): def __init__(self, varA, varB): super().__init__(varA, varB) """ some code """ 回答1: class Rectangle: def __init__(self, length, width): self.length = length self.width = width def area(self): return self.length * self.width def perimeter(self): return 2 * self.length + 2 * self.width class Square(Rectangle): def __init__(self, length): super(Square, self)

问题 I have a program where I use cout to emit debug information. The code is executed in the initialization of a static global variable, i.e. quite early in the program execution. When I use my own build script to build the program, it segfaults at the first use of cout (only a string literal is shifted into cout, so it cannot be the value). I used valgrind to check for earlier writes to invalid locations, but there are none (and there is also no code that would be likely to generate those writes

问题 I have a program where I use cout to emit debug information. The code is executed in the initialization of a static global variable, i.e. quite early in the program execution. When I use my own build script to build the program, it segfaults at the first use of cout (only a string literal is shifted into cout, so it cannot be the value). I used valgrind to check for earlier writes to invalid locations, but there are none (and there is also no code that would be likely to generate those writes

问题 I have a program where I use cout to emit debug information. The code is executed in the initialization of a static global variable, i.e. quite early in the program execution. When I use my own build script to build the program, it segfaults at the first use of cout (only a string literal is shifted into cout, so it cannot be the value). I used valgrind to check for earlier writes to invalid locations, but there are none (and there is also no code that would be likely to generate those writes

问题 I have a program where I use cout to emit debug information. The code is executed in the initialization of a static global variable, i.e. quite early in the program execution. When I use my own build script to build the program, it segfaults at the first use of cout (only a string literal is shifted into cout, so it cannot be the value). I used valgrind to check for earlier writes to invalid locations, but there are none (and there is also no code that would be likely to generate those writes

问题 I was reading a book on Java and came across an example in which an array of type double was initialized in a way that I haven't seen before. What type of initialization is it and where else can it be used? double m[][]={ {0*0,1*0,2*0,3*0}, {0*1,1*1,2*1,3*1}, {0*2,1*2,2*2,3*2}, {0*3,1*3,2*3,3*3} }; 回答1: This is array initializer syntax , and it can only be used on the right-hand-side when declaring a variable of array type. Example: int[] x = {1,2,3,4}; String y = {"a","b","c"}; If you're not