[Access Violation]: Debug Help

Just trying to put null characters into an array. Might sound easy.. but even this little snippet of code makes my pc go crazy.

This will compile, but will hang up at runtime.. and will cause an, "access violation" when ran through the debugger:

Code:

---

#include<iostream>
#include<cstring>
using namespace std;

int main()
{
        int iCount = 3;

       
        char **Lines = new char*[3];

        Lines[0] = "H1007, 1-24\0",
        Lines[1] = "A, 25-36\0",
        Lines[2] = "H1007, 37-48\0";

        //Visual Verification:  everything works fine
      for(int i=0; i<3; i++)       
               
                cout << Lines[i] << endl;


    char **Name = new char*[iCount];
    char **FiberCount1 = new char*[iCount];
    char **FiberCount2 = new char*[iCount];;
    int /*size,*/ word_index;
    bool cont = true;

    i=0;
    for(int j=0; i<iCount; i++, j=0)
    { 
       
        word_index = 0;
        cont = true;
       
        do{       
       
              //Extract Fiber Name
              while(Lines[i][j]!=',')
              {
                  j++;
              }
       
              //At this point, i==0 and j==5
              Lines[i][j]='\0';  //This line causes "access violation"
              Name[i] = new char[j-word_index+1];
              strcpy(Name[i], Lines[i]+word_index);
              //Name[i][j-word_index] = '\0';

...
...
...

---

any ideas/suggestions on what to do would be cool

using MVSC++ 6.0 (mostly for testing/debugging)

Try putting something else in instead of '\0' and see if you get an access violation.

tried a few different characters.. same results..

"unhandled exception.. ..access violation"

Make sure you're not going out of your bounds in your array. If you're reaching for an array element that higher than you declared, then your reaching for a memory address that doesn't belong to your program. Try changing i and j to 1 and 1 and see if it runs.

changed my array indexes.. same results... :confused:


I hold windows XP personally responsible for not properly allocating my memory. :cool:

Can you attach the full source to download? I'd like to mess around with it a bit.

It is because you are trying to modify a constant memory address. eg.

Code:

---

#include <iostream>

int main()
{
    char *test = "Hello";
    //Oh this works but it is a bad idea!
    test[0] = '\0';
   
    return 0;
}

---

This is ok though.

Code:

---

#include <iostream>
#include <cstring>

int main()
{
    //Allocate out
    char *sayHello = new char[strlen("Hello") + 1];
    std::strcpy(sayHello,"Hello");
   
    std::cout<<sayHello<<std::endl;
   
    //Now this is ok because you didn't assign the pointer to a const
    //memory address aka the string
    sayHello[0] = 'p';
   
    std::cout<<sayHello<<std::endl;
   
    std::cin.get();   
       
    return 0;
}

---

thanks hombre.. sounds like the moral of the story is.. 'thou shalt not attempt to modify a hard-coded statically declared string literal.." :)




Second Question:

Why does the following boolean test fail?

Code:

---

#include<iostream>
#include<cstring>
using namespace std;

int main()
{
        int iCount = 3;
       
        char **Lines = new char*[3];


        //Lines = {{"H1001, "1-24"}, {"A, 25-36"}, {"H1007, 36-45"}};

        Lines[0] = new char[strlen("H1007, 1-24\0")];
        Lines[1] = new char[strlen("A, 25-36\0")];
        Lines[2] = new char[strlen("H1007, 36-47\0")];

        strcpy(Lines[0], "H1007, 1-24\0");
        strcpy(Lines[1], "A, 25-36\0");
        strcpy(Lines[2], "H1007, 36-47\0");

        for(int i=0; i<3; i++)       
               
                cout << Lines[i] << endl;


    char **Name = new char*[iCount];
    char **FiberCount1 = new char*[iCount];
    char **FiberCount2 = new char*[iCount];;
    int /*size,*/ word_index;
        bool cont = true;

    i=0;
    for(int j=0; i<iCount; i++, j=0)
    { 
       
        word_index = 0;
                cont = true;
       
        do{       
       
              //Extract Fiber Name
              while(Lines[i][j]!=',')
              {
                  j++;
              }
       
              Lines[i][j]='\0';
              Name[i] = new char[j-word_index+1];
              strcpy(Name[i], Lines[i]+word_index);
              //Name[i][j-word_index] = '\0';
       
              word_index = j;
                          word_index++;
       
              //Extract Beginning Fiber Count
              while(Lines[i][j]!='-')
              {
                  j++;
              }
       
              Lines[i][j] = '\0';
              FiberCount1[i] = new char[j-word_index+1];
              strcpy(FiberCount1[i], Lines[i]+word_index);
              //FiberCount1[i][j-word_index] = '\0';
       
              word_index = j;
                          word_index++;
       
              //Extract Ending Fiber Count - Code works fine up until this point
              //Even when the null character is reached.. the loop continues infinately
              while(Lines[i][j]!=',' || Lines[i][j]!='\0')   
              {
                  j++;
              }

              if(Lines[i][j]=='\0')

                                  cont = false;
       
              Lines[i][j] = '\0';
              FiberCount2[i] = new char[j-word_index+1];
              strcpy(FiberCount2[i], Lines[i]+word_index);
              //FiberCount2[i][j-word_index] = '\0';
       
          }while(cont); 
        }

        return 0;

}

---

When viewed through the debugger.. it appears that even when Lines[i][j] equals NULL.. the loop continues on..?!?@

*just for fun.. I just threw in a comma in place of the null character.. and the debugger saw the comma.. but the loop continued to loop.. :rolleyes:

Thou shalt use and "&&". Remeber || means or. So if(1==1|| 2 == 1) it will go through because one of the conditions is true.

Code:

---

#include <iostream>

int main()
{
    if(1 == 1 || 2 == 1)
    {
        std::cout<<"It works!!!!!!!! #1"<<std::endl;
    }
   
    if(1 == 1 && 2 == 1)
    {
        std::cout<<"It works!!!!!!!! #2"<<std::endl;
    }
   
    std::cin.get();
   
    return 0;
}

---

And no I will not make out with you. :)

jesus I am an idiot..!@#!@#

Let's check with the survey.

Survey Says: You are an idiot :).

I think the survey is correct..!@#




Parsing goodness.. thanks to senor bling :cool:

Code:

---

#include<iostream>
#include<cstring>
#include<iomanip>
using namespace std;

int main()
{
        int iCount = 3;

        //Parse User Entered Text
        char **Lines = new char*[3];


        //Lines = {{"H1001, "1-24"}, {"A, 25-36"}, {"H1007, 36-45"}};

        Lines[0] = new char[strlen("H1007, 1-24\0")+1];
        Lines[1] = new char[strlen("A, 25-36\0")+1];
        Lines[2] = new char[strlen("H1007, 36-47\0")+1];

        strcpy(Lines[0], "H1007, 1-24\0");
        strcpy(Lines[1], "A, 25-36\0");
        strcpy(Lines[2], "H1007, 36-47\0");

        for(int i=0; i<3; i++)       
               
                cout << Lines[i] << endl;


    char **Name = new char*[iCount];
    char **FiberCount1 = new char*[iCount];
    char **FiberCount2 = new char*[iCount];;
    int /*size,*/ word_index;
        bool cont = true;

    i=0;
    for(int j=0; i<iCount; i++, j=0)
    { 
       
        word_index = 0;
        cont = true;
       
        do{       
       
              //Extract Fiber Name
              while(Lines[i][j]!=',')
              {
                  j++;
              }
       
              Lines[i][j]='\0';
              Name[i] = new char[j-word_index+1];
              strcpy(Name[i], Lines[i]+word_index);
              //Name[i][j-word_index] = '\0';
       
              word_index = j;
              word_index++;
       
              //Extract Beginning Fiber Count
              while(Lines[i][j]!='-')
              {
                  j++;
              }
       
              Lines[i][j] = '\0';
              FiberCount1[i] = new char[j-word_index+1];
              strcpy(FiberCount1[i], Lines[i]+word_index);
              //FiberCount1[i][j-word_index] = '\0';
       
              word_index = j;
              word_index++;
       
              //Extract Ending Fiber Count
              while(Lines[i][j]!=',' && Lines[i][j]!='\0') 
              {
                  j++;
              }

              if(Lines[i][j]=='\0')

                  cont = false;
       
              Lines[i][j] = '\0';
              FiberCount2[i] = new char[j-word_index+1];
              strcpy(FiberCount2[i], Lines[i]+word_index);
              //FiberCount2[i][j-word_index] = '\0';

              word_index = j;
              word_index++;
       
          }while(cont); 
        }


        cout << endl << endl << endl
            << setw(20) << "Fiber Name" << setw(20) << "Beginning Count" << setw(20) << "Ending Count"  << endl
            << setw(20) << "----------" << setw(20) << "---------------" << setw(21) << "------------\n" << endl
            << setw(20) << Name[0]      << setw(20) << FiberCount1[0]    << setw(20) << FiberCount2[0]  << endl
            << setw(20) << Name[1]        << setw(20) << FiberCount1[1]    << setw(20) << FiberCount2[1]  << endl
            << setw(20) << Name[2]      << setw(20) << FiberCount1[2]    << setw(20) << FiberCount2[2]  << endl
            << endl << endl << endl ;

        return 0;

}

---

That's why they pay me the big bucks.

Any reason you're not using C++ to solve this?

cstring character arrays were taught in my cs201 class as part of the c++ curiculum.. walter savitch teaches it in his c++ series books.. petzold's book is entirely in c (using the above algorithm in a windows project) what's so wrong about using cstrings in me' code..?!?!?


"new" makes my code c++ :cool:

>> what's so wrong about using cstrings in me' code..?!?!?

Nothing. It's your choice. IMO many C++ programmers (especially beginners) would benefit from learning and using C++ tools, and many just use C versions because their class/instructor/book uses them and they don't know any better. I can see wanting to stay consistent when going through Petzold, but the algorithm above would be simpler, easier and safer (IMO) with C++ tools.

One thing I see is this Brain. You need to add + 1 on your new's because strlen does not count the null terminator. E.G

Code:

---

#include <iostream>
#include <cstring>

int main()
{
    unsigned int getLen = std::strlen("Hello\0");
   
    std::cout<<getLen<<std::endl;
   
    std::cin.get();
   
    return 0;
}

---

This is 5 not 6.

fixed...


good catch... :cool:


(so many little nuances to remember..!!! )

There's also no need to add the null terminator to the string literals. It is there automatically.