Setup std::vector in class constructor
c++, constructor, new-operator, stdvector
Solution
Just do:
MyClass::MyClass(int m_size) : size(m_size), vec(m_size, 0)
You already seem to know about initializer lists, why not initialize vector there directly?
vec = new vector<int>(size,0);
is illegal because `new` returns a pointer and in your case `vec` is an object.
Your second option:
vector<int> temp(size,0);
vec = temp;
although it compiles, does extra work for no gain. By the time you reach the assignment, two vectors would already have been constructed and discarded afterwards.
Problem
I'm designing a class that has a `std::vector<int>` as an instance variable. I'm using a `std::vector` because I need to set its size at runtime. Here are the relevant portions of my code: ``` my_class.h: #include <vector> using std::vector; class MyClass { int size; vector<int> vec; } my_class.cc: #include "my_class.h" using std::vector MyClass::MyClass(int m_size) : size(m_size) { vec = new vector<int>(size,0); } ``` When I attempt to compile I get these error messages: ``` g++ -c -Wall my_class.cc -o my_class.o my_class.cc: In constructor ‘MyClass::MyClass(int): my_class.cc:4 error: no match for ‘operator=’ in ‘((MyClass*)this)->My_Class::vec = ((*(const allocator_type*)(& std::allocator<int>())), (operator new(24u), (<statement>, ((std::vector<int>*)<anonymous>))))’ make: *** [my_class.o] Error 1 ``` However, when I change the offending line to: ``` vector<int> temp(size,0); vec = temp; ``` It now compiles without a hitch and I get the desired behavior and can access my vector as ``` vec[i] // i having been defined as an int yada yada yada ``` This workaround is okay, but I would like to understand why it works and the first method fails.