C++: Inputting text as char* throws IStream nullptr error

Asked Jul 22 '20 at 13:38

Active Jul 22 '20 at 13:38

Viewed 25 times

I am running a simple C++ program (Visual Studio 2017) that requires user input.

This is how I collect that input:

int main()
{
    char* in;
    in = '\0';
    std::cout << "Move?\n";
    std::cin >> *in;
}

However, an exception is thrown on the last line:

Exception thrown: write access violation.
**_Ch** was nullptr.

When I take a closer look, the error is thrown from within the istream class at line 910:

template<class _Elem,
    ...

    if (_Ok)
        {   ...
        if (_Traits::eq_int_type(_Traits::eof(), _Meta))
            _State |= ios_base::eofbit | ios_base::failbit;
        else
            _Ch = _Traits::to_char_type(_Meta); // ERROR THROWN HERE

What am I doing wrong?

asked Jul 22 '20 at 13:38

Jessica Chambers

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3

Do not use `char*`. Use `std::string`. – n. m. could be an AI Jul 22 '20 at 13:40
2

you have a pointer to a char, but no character, and what you actually want is a string – 463035818_is_not_an_ai Jul 22 '20 at 13:40
@n.'pronouns'm. @idclev 463035818 I changed the type to a string, but the `std::cin >> in;` line then says that no operator found which takes a right hand argument of type "string" – Jessica Chambers Jul 22 '20 at 13:44
@TedLyngmo I made a typo, I did use ">>" – Jessica Chambers Jul 22 '20 at 13:48
1

Does your program look like [this](https://godbolt.org/z/bMqnad)? – Ted Lyngmo Jul 22 '20 at 13:50
@TedLyngmo yep that's it - though I did not include explicitly. – Jessica Chambers Jul 22 '20 at 13:54
1

@TedLyngmo explicitly importing solved the issue, thanks – Jessica Chambers Jul 22 '20 at 14:22

C++: Inputting text as char* throws IStream nullptr error

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