C++ String\ Vector initialization

Question

I have questions about C++ initialization.

In Java: if I want a empty StringBuffer, I should use

StringBuffer sb = new StringBuffer();

to initialize a empty string buffer.

In C++: If I want to use a empty string, I can just declare

std::string str; 

or std::string str = "";

In real world projects should I always write like the second form?

How about declare an empty vectors?

vector<int> vec;

Is this OK? or should I give some null values to this vec?

Answer 1

std:string and std:vector are classes, not basic types: That mean that unlike an Integer which as a pseudo-random value at the declaration moment, string and vectors has a well defined initial value.

The default value for std::string is "".

The default content for std::vector is {}.

You may use what you prefer, but the initialization is not necessary, and even not very optimal.

Answer 2

1. std::string str(""); It does a direct initialization and uses string(const char *) constructor.

2. std::string str=""; It does a copy initialization.

3. std::string str; It creates empty string.

Option 3 is just like others and less overhead. Use it Read more about the difference from here What's the motivation behind having copy and direct initialization behave differently?