initializing private class variable of std::string&

Question

How can I initialize my private variable in my c++ class?

a.h:

class A {
    private:
        std::string& name;
    public:
        A(void);
        ~A(void);

        bool load(std::string& name);
};

a.cpp:

#include <string>
#include "a.h"

A::A(void) {  
    this->name = "";  
}
A::~A(void) {}


bool A::load(std::string& name) {
    this->name = name;
}

The error:

a.cpp: In constructor ‘A::A()’:
a.cpp:3:1: error: uninitialized reference member in ‘std::__cxx11::string& {aka class std::__cxx11::basic_string<char>&}’ [-fpermissive]
 A::A(void) {
 ^
In file included from a.cpp:2:0:
a.h:3:22: note: ‘std::__cxx11::string& A::name’ should be initialized
         std::string& name;

I have initialized it in my constructor (in a.cpp), but it is still erroring.

Why do you need name to be a string&? Why no just a string? Making a class data member a reference is complicated stuff, because you cannot have it uninitialized to some actual string from the very beginning. — A.S.H
– A.S.H, Commented Dec 12, 2016 at 21:24

Sergey Kalinichenko · Accepted Answer · 2016-12-12 21:29:16Z

3

Let's fix the default constructor first: you cannot initialize references with an assignment. They need to be initialized with the initializer list:

static string empty_name("");

A::A(void) : name (empty_name) {  
}

Note the use of empty_name variable, scoped to translation unit. This lets you initialize a reference member to some object.

As far as the load member function goes, there is no way to re-assign a reference after it has been created. If you need this functionality, your best bet is to replace a reference with either a pointer if you need to access an external std::string object, or a copy (i.e. std::string name) if you do not need to reference a string that is external to your object.

answered Dec 12, 2016 at 21:29

Sergey Kalinichenko

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