What's the Difference???

I have been experimenting with different functions and created this little program that displays a box around a string

Code:

#include <windows.h>
#include <vector>
#include <string>

int main() {
    std::string text = "this is a test";
    HANDLE hOut = GetStdHandle(STD_OUTPUT_HANDLE);
    LPDWORD NumWritten;
    COORD position = {1, 1};
    std::string line, spaces;
    std::vector<std::string> box;
    std::vector<std::string>::iterator iter;
    std::string::size_type text_length = text.length();
    std::string::size_type box_length  = text_length + 2;
 
    char top_left_corner      = (unsigned char)201,
         top_right_corner     = (unsigned char)187,
         bottom_left_corner   = (unsigned char)200,
         bottom_right_corner  = (unsigned char)188,
         vert_sides           = (unsigned char)186,
         horz_sides           = (unsigned char)205;
    spaces.assign(text_length, ' '); 
    line.assign(text_length, horz_sides);

    //  create box
    box.push_back(top_left_corner + line + top_right_corner);    
    box.push_back(vert_sides + spaces + vert_sides);
    box.push_back(vert_sides + text + vert_sides);
    box.push_back(vert_sides + spaces + vert_sides);
    box.push_back(bottom_left_corner + line + bottom_right_corner);

    // display box
    for (iter = box.begin(); iter != box.end(); ++iter) {
        SetConsoleCursorPosition(hOut, position);
        WriteConsole(hOut, iter->c_str(), iter->length(), NumWritten, NULL);
        ++position.Y;
    }

    SetConsoleCursorPosition(hOut, position);
    system("pause");
    return 0;
}

this works fine. But when I do this

Code:

#include <windows.h>
#include <vector>
#include <string>

void display(std::string);

int main() {
    std::string text = "this is a test";
    display(text);
    system("pause");

    return 0;
}


void display(std::string text) {
    HANDLE hOut = GetStdHandle(STD_OUTPUT_HANDLE);
    LPDWORD NumWritten;
    COORD position = {1, 1};
    std::string line, spaces;
    std::vector<std::string> box;
    std::vector<std::string>::iterator iter;
    std::string::size_type text_length = text.length();
    std::string::size_type box_length  = text_length + 2;
 
    char top_left_corner      = (unsigned char)201,
         top_right_corner     = (unsigned char)187,
         bottom_left_corner   = (unsigned char)200,
         bottom_right_corner  = (unsigned char)188,
         vert_sides           = (unsigned char)186,
         horz_sides           = (unsigned char)205;
    spaces.assign(text_length, ' '); 
    line.assign(text_length, horz_sides);

    //  create box
    box.push_back(top_left_corner + line + top_right_corner);    
    box.push_back(vert_sides + spaces + vert_sides);
    box.push_back(vert_sides + text + vert_sides);
    box.push_back(vert_sides + spaces + vert_sides);
    box.push_back(bottom_left_corner + line + bottom_right_corner);

    // display box
    for (iter = box.begin(); iter != box.end(); ++iter) {
        SetConsoleCursorPosition(hOut, position);
        WriteConsole(hOut, iter->c_str(), iter->length(), NumWritten, NULL);
        ++position.Y;
    }

    SetConsoleCursorPosition(hOut, position);
    return;
}

I get an access viotation fault and the program crashes at the very end. I don't see what the problem is. The only thing I did different is put where the box is built and displayed in its own function.

BTW, I know that it is not a good idea to use system("pause"), but this is only an experiment.....

Try to move the declaration of the handle, to a global declaration:

Code:

#include <windows.h>
#include <vector>
#include <string>

void display(std::string);

HANDLE hOut;

int main() {
    std::string text = "this is a test";
    display(text);
    system("pause");

    return 0;
}


void display(std::string text) {
    hOut = GetStdHandle(STD_OUTPUT_HANDLE);
    LPDWORD NumWritten;
    COORD position = {1, 1};
    std::string line, spaces;
    std::vector<std::string> box;
    std::vector<std::string>::iterator iter;
    std::string::size_type text_length = text.length();
    std::string::size_type box_length  = text_length + 2;
 
    char top_left_corner      = (unsigned char)201,
         top_right_corner     = (unsigned char)187,
         bottom_left_corner   = (unsigned char)200,
         bottom_right_corner  = (unsigned char)188,
         vert_sides           = (unsigned char)186,
         horz_sides           = (unsigned char)205;
    spaces.assign(text_length, ' '); 
    line.assign(text_length, horz_sides);

    //  create box
    box.push_back(top_left_corner + line + top_right_corner);    
    box.push_back(vert_sides + spaces + vert_sides);
    box.push_back(vert_sides + text + vert_sides);
    box.push_back(vert_sides + spaces + vert_sides);
    box.push_back(bottom_left_corner + line + bottom_right_corner);

    // display box
    for (iter = box.begin(); iter != box.end(); ++iter) {
        SetConsoleCursorPosition(hOut, position);
        WriteConsole(hOut, iter->c_str(), iter->length(), NumWritten, NULL);
        ++position.Y;
    }

    SetConsoleCursorPosition(hOut, position);
    return;
}

I think both ought to crash, you're just getting lucky. NumWritten is your problem. You never initialize it, and pass a pointer to some random location in memory to WriteConsole. Furthermore, you never allocate any memory for the pointer to point to.

Declare NumWritten as a DWORD, not a LPDWORD. (Then pass &NumWritten)

Declare NumWritten as a DWORD, not a LPDWORD. (Then pass &NumWritten)

Ahh, I knew it was something simple. MSDN said that NUmWritten was a LPDWORD so that was what I used. I thought that I should be passing the address of NumWritten but it would not work since I was declaring it as a LPDWORD. Thanks, I'll do that and see what happens!