what do these arguments mean

[boonflies]

A.
test::NodeHandle private_nh
//creating a class
Driver::Driver(): private_nh("~"),
frame_id(-1),

what does ("~") in the above line of code.

B.
int32_t frame_id;
frame_id(-1)
what does (-1) in the above line of code. should not the line be,
frame_id = -1

[jonnin]

"~" is a string with a single character (~) in it. It is initializing a string variable like the -1 below.


the (-1) is correct in A. It is doing exactly that (frame_id is -1) but the syntax for initialization lists is a little different.

Both things in A are doing the same thing, just different variable types.

B should be as you said. Its legal and it works, but using () as a statement is cryptic and of no value here.

[icy1]

Suppose

class Driver
{
public:
    Driver(string home="~") : 
        frame_id_(-1),
        home_directory_(home)
    {
        normal_home_ = home_directory_=="~";
    }

private:
    int frame_id_;
    string home_directory_;
    bool normal_home_;
};

Variables in the initializer list are evaluated first, and constructor body (e.g. normal_home_) only afterwards. For context, "~" might be the home directory on linux-like systems.