Why is my function returning an empty string?

Question

I was wondering if someone could please illuminate me on why the below code does not behave the way I expect. By that I mean I expect the line

std::cout << myEngine.getDesc() << std::endl;

to print out: "Desc1"

But I get an empty string? I figured that maybe it was because I was splitting up my rudimentary code into different files incorrectly but I get the same thing when I put all the code into one file.

StringErrorTest.cpp

#include <iostream>
#include "Engine.h"


int main()
{
    std::cout << "Compiling & Running!";
    Engine myEngine;
    std::string t1 = "Hello ";
    std::cout << myEngine.getDesc() << std::endl;
    std::cout << t1 << std::endl;
    return 0;
}

Engine.h

#include <string>

class Engine {
private:
    std::string m_Description;
    std::string m_Description2;

public:
    Engine();
    std::string getDesc();
    void setDesc(std::string desc);
    std::string getDesc2();
    void setDesc2(std::string desc2);
    std::string spitItOut();

};

Engine.cpp

#include "Engine.h"

Engine::Engine()
{
    std::string m_Description = "Desc1";
    std::string m_Description2 = "Desc2";
}

std::string Engine::getDesc()
{
    return m_Description;
}

std::string Engine::getDesc2()
{
    return m_Description2;
}

By the way I did search for similar questions but they were all a bit more complex than mine. I feel I have a very basic misunderstanding going on here.

In your constructor you define local variable m_Description. Change std::string m_Description = "Desc1"; to m_Description = "Desc1"; (i.e. remove std::string part). — freakish
– freakish, Commented Mar 16, 2020 at 7:51

songyuanyao · Accepted Answer · 2020-03-16 07:54:16Z

4

In Engine::Engine(), you're creating two local objects named m_Description and m_Description2, which have nothing to do with the data members with same names; they hide the names of data members.

What you want to is to assign them as

Engine::Engine()
{
    m_Description = "Desc1";  // or this->m_Description = "Desc1"
    m_Description2 = "Desc2"; // or this->m_Description2 = "Desc2"
}

Or initialize them as

Engine::Engine() : m_Description("Desc1"), m_Description2("Desc2")
{
}

edited Mar 16, 2020 at 7:54

answered Mar 16, 2020 at 7:52

songyuanyao

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2 Comments

yoonsi Over a year ago

I understand now.. thank you so much. I'm sorry for such a silly question.

Fareanor Over a year ago

@yoonsi Since this answers your question, you can accept the answer.

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