Is using assign() a good way to initialise my C++ vector of structs?

问题

The struct

struct Vanish
{
  int iCount;
  int iRow;
};

I defined a std::vector of Vanish as a member of my class, and want to initialise it in the constructor like this:

class BigClass
{
  public:
    BigClass();
  private:
    std::vector<Vanish> tovanish;
};

void BigClass::BigClass()
{
  Vanish empty = {0,0};
  tovanish.assign(MAX_VANISH, empty);
}

Is there a better way, or is this considered OK?

回答1:

It is better to do that in the constructor's initializer list:

BigClass::BigClass()
: tovanish(MAX_VANISH)
{

}

That way, you'll avoid possible vector reallocations. Note that you vector's constructor will value-initialize its elements. Value-initialization of the int members in Vanish just zeroes them.

Note that in C++11, using uniform-initialization you could specify other values easily:

BigClass::BigClass()
: tovanish(MAX_VANISH, {42, 24})
{

}

回答2:

Is there a better way?

Yes, sure,

BigClass::BigClass() : tovanish(MAX_VANISH) {}

This gives you a vector with MAX_VANISH value-initialized Vanish elements.

来源：https://stackoverflow.com/questions/17003126/is-using-assign-a-good-way-to-initialise-my-c-vector-of-structs