Unhandled exception at Access violation reading location ***

Question

I got the error: "Unhandled exception at 0x00d23737 in Test.exe: 0xC0000005: Access violation reading location 0x8a8c0344" This happens when i execute the following code:

int main(int argc, char* argv[])
{
string My_String_Array[30720];
Initialize_My_String_Array (My_String_Array); //i really doubt that there is something wrong in the definition of this function
for (int i=0;i<=30719;i++)
    {
    cout<<My_String_Array[i]<<endl;
    }
system("pause");
return 0;
}

The code to Initialize_My_String_Array() is as follows:

void Initialize_My_String_Array (My_String_Array[30720])
{   
    string Initialization_Values[]={"A","B","C","D","E"};
    int Index=0;
    int i=0;
    int j=0;
    while (i<=30719)
        {   

            My_String_Array[i]=Initialization_Values[Index];
            i++;
            j++;
            if (j=6144)
                {
                j=0;
                Index++;
                }
        }

Any thoughts would be appreciated.

You need to spend some time properly learning C++. The code on display here contains some rather significant syntax errors. — Xirema, Jan 20 '17 at 17:23
So you've got 2 arrays being accessed - have you worked out which one is causing you the problem yet? — UKMonkey, Jan 20 '17 at 17:25
@Xirema thanks for your answer, but could you specify what is the syntax error please ? — Abdelrahman, Jan 20 '17 at 17:25
@NathanOliver, the question you linked has a different problem than what the problem this user is having. This is not a duplicate of that question. — Xirema, Jan 20 '17 at 17:29
Simplify your problem then - try removing the Initialization_Values[value] from the equation — UKMonkey, Jan 20 '17 at 17:30
@Xirema No it doesn't. Both questions are trying to assign into default constructed strings with `[]`. — NathanOliver, Jan 20 '17 at 17:30
@NathanOliver Reread the first part of the code. `My_String_Array` is declared as a `string[]`, not a `string`. — Xirema, Jan 20 '17 at 17:31
@Xirema Oh jeez. I thought he was at a single string there. Reopend — NathanOliver, Jan 20 '17 at 17:32
I mean really, this is a question about using your debugger - what you really want to do is put a conditional breakpoint in, and catch the moment where either i or Index is out of range for the array. Alternately - you could use a std::vector and let that throw when you try to access something out of range. — UKMonkey, Jan 20 '17 at 17:37
`if(j=6144)` does not check if `j` is equal to 6144 (it assigns 6144 to `j`), so your `Index` value probably goes past 4 pretty quickly. — Peter Ritchie, Jan 20 '17 at 17:39
Use `std::vector`; you'll have this fixed up in no time and can spend the weekend chilling. — Bathsheba, Jan 20 '17 at 17:44

score 6 · Accepted Answer · edited May 23 '17 at 10:29

There are a number of problems in your code, particularly in Initialize_My_String_Array.

void Initialize_My_String_Array (My_String_Array[30720])
{   
    string Initialization_Values[]={"A","B","C","D","E"};
    int Index=0;
    int i=0;
    int j=0;
    while (i<=30719){
        My_String_Array[i]=Initialization_Values[Index];
        i++;
        j++;
        if (j=6144){
            j=0;
            Index++;
        }
    }
}

Your method signature is incorrect. You've declared a variable My_String_Array[30720], but you haven't given it a type. From context, I think the type is supposed to be std::string.
In the if statement, you've written if(j = 6144). = is not the equality operator, it is the assignment operator. == is the equality operator. Your code is assigning 6144 to j, then promoting the (non-zero) value to a boolean, which makes the if statement always execute, which means Index is always incremented. Within 5 iterations of the loop, Index is incremented beyond the size of Initialization_Values, which causes Undefined Behavior, and in your case, causing access violations.

Based on the context, I think the corrected code looks like this:

//Type is now correctly defined.
void Initialize_My_String_Array (string My_String_Array[30720])
{   
    string Initialization_Values[]={"A","B","C","D","E"};
    int Index=0;
    int i=0;
    int j=0;
    while (i<=30719){
        My_String_Array[i]=Initialization_Values[Index];
        i++;
        j++;
        if (j == 6144){
            j=0;
            Index++;
        }
    }
}

Beyond this, you need to spend some time reevaluating how you've written this code. C-style arrays are generally considered to be bad practice in C++, and your code is a perfect case-study as to why. C++ std::array objects are far superior, and should be preferred for any code like this. On top of that, you've indulged in some spaghetti code involving indexes and array bounds. There are much better ways to handle it. I've written what I consider to be a much better version of this code:

void Initialize_My_String_Array (std::array<std::string, 30720> & My_String_Array)
{   
    const std::array<std::string, 5> Initialization_Values{"A","B","C","D","E"};
    const size_factor = (My_String_Array.size() / Initialization_Values.size());
    for(size_t index = 0; index < My_String_Array.size() && (index / size_factor) < Initialization_Values.size(); index++) {
        My_String_Array[index] = Initialization_Values[index / size_factor];
    }
}

int main(int argc, char* argv[]) {
    std::array<std::string, 30720> My_String_Array;
    Initialize_My_String_Array (My_String_Array);
    for(std::string const& s : My_String_Array) {
        std::cout << s << std::endl;
    }
    system("pause");
    return 0;
}

One more thing: somewhere in your code, you've written something like using namespace std;. Get rid of it. It's bad practice and makes your code harder to interpret for other users ("Is string a custom type or std::string?")

Thank you very much,, your answer is very helpful,, i really appreciate your time,, — Abdelrahman, Jan 20 '17 at 17:51

Unhandled exception at **** Access violation reading location *******

1 Answers1

Unhandled exception at Access violation reading location ***