C++ and initialize const variable

Question

I want to create class Test with const int variable with name "a". After that I need create constructor where variable "a" get value =10. I Create class test and in test.h I create const int a; in class Test.h and in test.cpp I have something like that:

#include "stdafx.h"
#include "Test.h"


Test::Test(void)
{
    a = 10;
    b = 20;
    size = 20;
    tekst[size];
    }

Test::~Test(void)
{
}

and this is test.h:

#pragma once
class Test
{

    const int a;  



public:
    Test(void);
    ~Test(void);
    int b;
    char *tekst;
    int size;
    static double d;
    int y;
};

but I get error:

Error   1   error C2758: 'Test::a' : must be initialized in constructor base/member initializer list    c:\users\bożydar\documents\visual studio 2012\projects\consoleapplication1\consoleapplication1\test.cpp 6
Error   2   error C2166: l-value specifies const object c:\users\bożydar\documents\visual studio 2012\projects\consoleapplication1\consoleapplication1\test.cpp 7

I'm sure searching constructor base/member initializer list on Google will pull up some good results. — Qaz
– Qaz, Commented Nov 16, 2012 at 14:34

Aesthete · Accepted Answer · 2012-11-16 14:34:04Z

7

The error says it all, a must be initialized in constructor base/member initializer list

Test::Test(void) : a(10) // Initializer list
{
...
}

answered Nov 16, 2012 at 14:34

Aesthete

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Comments

john · Accepted Answer · 2012-11-16 14:34:11Z

3

The error tells you what to do

Test::Test(void) : a(10) // an initializer list
{
    b = 20;
    size = 20;
    tekst[size];
}

BTW i think you'll find that the code

tekst[size];

does not do what you expect it to. Probably you mean

tekst = new char[size];

answered Nov 16, 2012 at 14:34

john

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1 Comment

Kerrek SB Over a year ago

The initializer list should be used for everything, not just for those cases where you absolutely must... And the local declaration of tekst is completely off.

Maroun · Accepted Answer · 2012-11-16 14:35:14Z

1

You have to do it in an initialization list:

Test::Test(void) : a(10) {
  ...
}

answered Nov 16, 2012 at 14:35

Maroun

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Comments

rodrigo · Accepted Answer · 2012-11-16 14:35:31Z

0

a is const, so you cannot assign to it. You must, however, initialize it.

Do:

Test::Test(void)
:a(10)
{
    ...
}

BTW, the tekst[size] doesn't do what you think, probably. It does nothing!

answered Nov 16, 2012 at 14:35

rodrigo

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1 Comment

Robᵩ Over a year ago

It might do nothing. It might do something. Technically, its behavior is undefined.

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