Having trouble with a string. Debug is claiming "bad pointer"

Question

I'm writing a program that acts as a number system converter and haven't even made it to the fun math and number values part before screwing up.

At the very end I declared a string "value_array" and it is has a "bad ptr" note on it when I step through the program. This is impeding me from moving on.

#include <iostream>
#include <ctype.h>
#include <stdlib.h>
#include <string>

using namespace std;

int main()
{
//Initialization:
int base = 0;
int target = 0;
int i = 0;

//Won't exit until the user inputs a viable number for a base (between 1 and 16 inclusively).
for (i = 0; i < 1; i += 0)
{
    cout << "Enter the base number system: ";
    cin >> base;
    cout << endl;

    if (base>=2 && base<=16)
    {
        i++;
    }

    else
    {
        cout << "Invalid value. Please input a value between 1 and 16 inclusively." << endl;
    }
}


//Same as before but makes sure the target is a valid number.

for (i = 0; i < 1; i += 0)
{
    cout << "Enter the target number system: ";
    cin >> target;
    cout << endl;

    if (target>=2 && target<=16)
    {
        i++;
    }

    else
    {
        cout << "Invalid value. Please input a value between 1 and 16 inclusively." << endl;
    }
}

string value_array = ""; //editted

cout << "Enter value in base (with no spaces): ";
cin >> value_array; //editted 

//int k = basevalue(value_array,base);//Please disregard. Can't use this function until the strings are usable.

return 0;
}

You *have* use `std::cin` and the input operator `>>` before, what makes you think it's different with a `std::string` object like `value_array`? You can use `std::cin >> value_array;` just like you did e.g. `std::cin >> target;` earlier in the program. — Some programmer dude, Sep 17 '15 at 06:15
That's the first thing I tried. I get "no operator '>>' meets these operands" — rynoclank, Sep 17 '15 at 06:20
If you get build errors, please include hem in your question, *complete* and *unedited*. — Some programmer dude, Sep 17 '15 at 06:29
Oh, and you seem to have *two* different problems, one is the compilation error and one is the crash/abnormal exit. You should concentrate on one problem here in this question, and ask another question for the other problem. — Some programmer dude, Sep 17 '15 at 06:38

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

1

You can use std::cin on value_array, but first remove constness. You can't modify const string.

Edit

You have to #include <string>.

edited Jun 20 '20 at 09:12

Community

1
1

answered Sep 17 '15 at 06:21

Alvarey

91
5

Ok I removed the const but the ">>" is still showing an error. – rynoclank Sep 17 '15 at 06:27
"No operator '>>' matches these operands" – rynoclank Sep 17 '15 at 06:32
@rynoclank That error usually comes with more information, please *edit your question* to include the *complete* error output. – Some programmer dude Sep 17 '15 at 06:34
@rynoclank Could you add full output in your question? – Alvarey Sep 17 '15 at 06:34
That's what it what it was. Thanks so much @Alvarey! I'll update the question. Any idea about why value_array has the "bad ptr" on it when I step through the program? – rynoclank Sep 17 '15 at 07:53
@rynoclank No problem. I have no idea why you get `bad ptr` in debugger. – Alvarey Sep 17 '15 at 08:02

score 0 · Answer 2 · edited May 23 '17 at 11:44

The problem you experience is caused by the constness by value_array. You declared it const which means that it cannot be modified by anything (it is read-only) during it's lifetime. Thus when you try to assign a string obtained from user input to it, compiler informs you that it is impossible. Everything works fine after removal of the const keyword.

It's hard to say what is the exact reason of the bad pointer error you experience. According to this answer it can be caused by inappropriate usage of raw pointers. If you use them somewhere after the above code, make sure any of them is NULL, nullptr nor 0 when used.

I modified your code a little bit and added a few comments, I hope they will be useful during development of your program:

#include <iostream>
#include <ctype.h>
#include <stdlib.h>

using namespace std;

int main()
{
    //Initialization:
    int base = 0;
    int target = 0;

    //PiotrSliwa: The loop can be removed with if-statement modified like below
    cout << "Enter the base number system: ";
    cin >> base;
    cin.ignore(1024, '\n'); // PiotrSliwa: ignore up to 1024 characters or until newline is found in order to avoid bugs caused by more-than-required user input characters
    cout << endl;

    if (base<2 || base>16)
    {
        cout << "Invalid value. Please input a value between 1 and 16 inclusively." << endl;
        return 0;
    }

    //PiotrSliwa: The loop can be removed with if-statement modified like below
    cout << "Enter the target number system: ";
    cin >> target;
    cin.ignore(1024, '\n');
    cout << endl;

    if (target<2 && target>16)
    {
        cout << "Invalid value. Please input a value between 1 and 16 inclusively." << endl;
        return 0;
    }

    string value_array = ""; //PiotrSliwa: removed 'const' from string which caused an error
    cout << "Enter value in base (with no spaces): ";
    cin >> value_array; //PiotrSliwa: The simplest method of obtaining user input and redirecting it to 'string' variable
    cin.ignore(1024, '\n');

    //int k = basevalue(value_array,base);//Please disregard. Can't use this function until the strings are usable.

    return 0;
}

Live demo

Also, consider enclosing functionalities into functions (or objects) to avoid code duplications as well as to provide reusable code and improve readability. For example:

#include <iostream>
#include <ctype.h>
#include <stdlib.h>

using namespace std;

template<typename T>
T getUserInput(string message)
{
    cout << message;
    T input;
    cin >> input;
    cin.ignore(1024, '\n');
    cout << endl;
    return input;
}

bool isValidNumberSystem(int numberSystem)
{
    return numberSystem>=2 && numberSystem<=16;
}

int main()
{
    int base = getUserInput<int>("Enter the base number system: ");
    if (!isValidNumberSystem(base))
    {
        cout << "Invalid value. Please input a value between 1 and 16 inclusively." << endl;
        return 0;
    }

    int target = getUserInput<int>("Enter the target number system: ");
    if (!isValidNumberSystem(target))
    {
        cout << "Invalid value. Please input a value between 1 and 16 inclusively." << endl;
        return 0;
    }

    string value_array = getUserInput<string>("Enter value in base (with no spaces): ");

    //int k = basevalue(value_array,base);//Please disregard. Can't use this function until the strings are usable.

    return 0;
}

Live demo

Having trouble with a string. Debug is claiming "bad pointer"

2 Answers2

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