Simple Pointer Problem

This is a discussion on Simple Pointer Problem within the C++ Programming forums, part of the General Programming Boards category; Hi i am trying to get a pointer to output text if it is possible but i dont understand where ...

  1. #1
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    Simple Pointer Problem

    Hi

    i am trying to get a pointer to output text if it is possible but i dont understand where i am going wrong

    this is the code i have come up with so far

    Code:
      
    #include <iostream>
    using namespace std;
     
    int main()
    {
      char name[10];
      char *ptr;
    
      ptr = &name[40];
      cin>>name;
      cin.ignore();
      cout<< *ptr <<"\n";
      cin.get();
    
    }
    when i do run the program i get some weird symbol. is this because it is just pointing to the memory address location?

    Thanks

  2. #2
    C++ Witch laserlight's Avatar
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    For starters, name[40] is accessing the array beyond its boundary.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
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    well i have modified it a bit and i can get one letter from the charactures i have entered but it does not display the rest of them is

    here is the update.

    Code:
      char name[10];
      char *ptr;
    
      ptr = name[10];
      cin>>name;
      cin.ignore();
      cout<< *ptr <<"\n";
      cin.get();
    also another question is that i have 3 pointers in a program it there any way of changing this

    Code:
    struct example {
    int x;
    int y;
    int z;
    };
    
    int main()
    {
    example structure;
    example number;
    example final;
    example *ptr;
    example *ptr2;
    example *ptr3;
    
    structure.x = 1;
    number.y = 123;
    final.z = 1772748757;
    ptr = &structure;
    ptr2 = &number;
    ptr3 = &final;
    
    cout<< ptr->x <<"\n\n";
    cout<< ptr2->y <<"\n\n";
    cout<< ptr3->z;
    cin.get();
    is there away to make ptr 1, 2, 3 one pointer or do they have to be all seperate?

    Thanks

  4. #4
    C++ Witch laserlight's Avatar
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    I suggest that you read the tutorials on arrays and pointers.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  5. #5
    Kernel hacker
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    Code:
      ptr = name[10];
    This part is definitely and completely broken - it sets the pointer to the value of a char [that is one beyond the size of your actual array] [[and your array has not been initialized, so the behavious is completely undefined, not that you'd want to initiialize it beyond it's size anyways]]. If you want your pointer to point at name, use:
    Code:
    ptr = name;
    // or
    ptr = &name[0];
    // or - if you don't want the FIRST char:
    ptr = &name[5];
    It's not clear to me what you want to change in your second example. If you want to print the content from three different structures, you need to set a pointer three times - of course, you can reuse the same pointer multiple times, but that would mean changing the pointer between each output. A single pointer can only point at one location at any given time, but you can of course change the pointer to point at anything else whenever you like.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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