a = new char[6] and yet a is much longer than 6?!?

Hi people, Im making a text editor and I have a big problem, here is the code where I have the problem

Code:

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mytext = new char[count+lenght];

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I have debugged my program many times and Im sure that count == 0 and lenght == 6, yet mytext always ends up bigger and when I print it on the screen it ends up printing a lot of giberish thats shouldnt be there!

Here is the .cpp file

Code:

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#include "main.h"

int main() {
        Text paper;
        char test[] = "Marcos";

        paper.addtext(test, strlen(test));
        paper.showtext();
        return 0;
}

// Class Text
Text::Text() {
        mytext = new char[1];
        mytext = NULL;
        count = 0;
}

Text::~Text() {
        delete[] mytext;
}

void Text::addtext(char *a, int lenght) {
        char *temp; // temporarily hold what was already on mytext

        if (mytext != NULL) {
                temp = new char[count];
       
                strcpy(temp, mytext);
       
                delete[] temp;
        } else {
                temp = "";
        }

        delete[] mytext;

        mytext = new char[count+lenght]; // make it long enough to hold what it had before + what we will add new
        for (int i = 0; i < count; i++)
                mytext[i] = temp[i]; // add what we had before

        for (int i = 0; i < lenght; i++)
                mytext[count+i] = a[i]; // add the new text after what we had before
}

void Text::deletetext() {
}

void Text::showtext() {
        printf("%s", mytext);
}

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Here is the .h file

Code:

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#include <stdlib.h>
#include <fstream>

class Text {
public:
        Text();
        ~Text();

        void addtext(char *, int);
        void deletetext();
        void showtext();
private:
        char *mytext;
        int count;
};

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Sorry for the trouble guys, but I really cant solve this.

Long story short you did not allow for the null terminating character '\0'.

Code:

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mytext = new char[count+lenght];

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maybe,

Code:

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mytext = new char[(count+lenght)+1];

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and

Code:

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        for (int i = 0; i < lenght; i++)
                mytext[count+i] = a[i]; // add the new text after what
                mytext[lenght] = '\0';//add null terminating character

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Thanks. :)

Hello Marcos,

I just had a quick scan through your program, and from what I can see there are a few other issues besides what Anubis has mentioned.

When you instantiate "Text", the internal variable "mytext" is assigned "new char[1]", then immediately assigned NULL, which means that you've leaked memory straight away.

Next, when you call "addtext" on this object (ie. for the first time) "mytext" is NULL, and "temp" will be pointed at a static empty char buffer. Then, you "delete[] mytext", which will break because at this point "mytext" is NULL.

You never update your internal "count" variable, which means when you repeatedly call the "addtext" function you'll never retain the text you had before.

-- insert Anubis' post here --

Have a go at fixing up these issues, and let us know how you go.

Good luck :)

Quote:

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Then, you "delete[] mytext", which will break because at this point "mytext" is NULL.

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Deleting a NULL pointer is a perfectly legal no-op.

Good point, I guess I'm still oldschool ;)

Thanks for the interest people, I have done some work on it and now it works (bearly :p )
This is what I have now in the .cpp file:

Code:

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#include "main.h"

int main() {
        Text paper;
        char buff[100];

        while (1) {
                scanf("%s", buff);
                rewind(stdin);
                if (!strcmp(buff, "-exit"))
                        break;
                paper.addtext(buff, strlen(buff));
        }

        paper.savetofile();
        return 0;
}

// Class Text
Text::Text() {
        mytext = new char;
        mytext = NULL;
        count = 0;
}

Text::~Text() {
        delete[] mytext;
}

void Text::addtext(char *a, int lenght) {
        char *temp;

        if (mytext != NULL) {
                temp = new char[count];

                for (int i = 0; i < count; i++)
                        temp[i] = mytext[i];

                temp[count] = NULL;
        } else {
                temp = "";
        }

        delete[] mytext;

        mytext = new char[(count+lenght)+1];

        for (int i = 0; i < count; i++)
                mytext[i] = temp[i];

        for (int i = 0; i < lenght; i++)
                mytext[count+i] = a[i];

        mytext[count+lenght] = NULL;

        count += lenght;
}

void Text::deletetext() {
}

void Text::showtext() {
        printf("%s", mytext);
}

void Text::savetofile() {
        std::ofstream fout;

        fout.open("Text.txt");
        fout << mytext << "\n";
        fout.close();
}

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Im not really sure if this fixed the memory leak, (I dont quite understand them yet).
Also, I was wondering what function I could use in main() to get a whole sentence because scanf() apearently stops reading after a space.

fgets() reads until a newline of EOF or until a specified number of characters has been read in.

edit:: This is C++, so you can use getline() and specify your own delimiter.

Quote:

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Originally Posted by Marcos

Code:

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...

// Class Text
Text::Text() {
    mytext = new char;  // Get rid of this line to fix memory leak
    mytext = NULL;
    count = 0;
}

...

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Im not really sure if this fixed the memory leak, (I dont quite understand them yet).

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No, you haven't solved the memory leak, see above in red.

Ok, so I finally got rid of the memory leak.
But I dont understand what I should put in the first parameter of getline() (_Istr).
Can someone use it in an example?

Quote:

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Originally Posted by Marcos

Ok, so I finally got rid of the memory leak.
But I dont understand what I should put in the first parameter of getline() (_Istr).
Can someone use it in an example?

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For your purposes, I think you would want:

Code:

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cin.getline(buff,sizeof(buff),'\n');

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Yeah that worked great, thanks :)

>I guess I'm still oldschool
Of what old school do you speak? Freeing a null pointer has always been a no-op, IIRC. ;)