Accelerated C++ 笔记

Exercise 1-2

Are the following definitionsvalid? Why or why not?

const std::string exclam = "!";

const std::string message = "Hello" + ", world" + exclam;

Solution

The first line is valid because it initializes the variable exclaim with the value "!".The second line is not valid, however. The reason is that the +operator is left-associative. This means that it is being used to concatenate "Hello"and ", world", which is not legal because one of the operands must be a std::string object. In the exercise, "Hello"and", world" are both string literals.