Arrays of pointers...

This is a discussion on Arrays of pointers... within the C++ Programming forums, part of the General Programming Boards category; Hello, I have a problem. I need to make an array of pointers, without knowing beforehand the size of the ...

  1. #1
    Programming Ninja In-T...
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    Arrays of pointers...

    Hello,
    I have a problem. I need to make an array of pointers, without knowing beforehand the size of the array. Is this possible?

    Code:
    const char* arrayOfPointers[];

  2. #2
    Guest Sebastiani's Avatar
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    Quote Originally Posted by Programmer_P View Post
    Hello,
    I have a problem. I need to make an array of pointers, without knowing beforehand the size of the array. Is this possible?

    Code:
    const char* arrayOfPointers[];
    Sure:

    Code:
    int main( void )
    {
        const char** arrayOfPointers = 0;
        // sometime later
        unsigned size = 1024;
        arrayOfPointers = new const char*[ size ];
        // do something usefull
        delete [ ] arrayOfPointers;
    }
    Thing is, though, you have to remember to delete the memory. A much better way is to use an std::vector, or similar, eg:

    Code:
    #include <vector>
    
    int main( void )
    {
        std::vector< const char* > arrayOfPointers;
        // sometime later
        unsigned size = 1024;
        arrayOfPointers.resize( size );
        // do something useful...memory will be deleted by vector object...
    }



    ITSA
    Socket Library!

  3. #3
    Programming Ninja In-T...
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    Thank you.
    Quick question:

    Can an element of an array of pointers be assigned a string, or just a single character?

  4. #4
    Registered User jeffcobb's Avatar
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    if it is an array of char * ptrs sure...
    C/C++ Environment: GNU CC/Emacs
    Make system: CMake
    Debuggers: Valgrind/GDB

  5. #5
    Programming Ninja In-T...
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    How about this?
    Code:
    string* str = NULL;
    str = new string;
    *str = "Yes, a string...\n";
    *str += "Yes, another string...\n";
    *str += "Yes, even another string...\n";
    int sizeOfStr = str->size();
    char* arrayOfPointers[] = NULL;
    //several code lines later...
    arrayOfPointers = new char*[sizeOfStr];
    string* anotherStr = NULL;
    anotherStr = new string;
    
    void doStuff();
    void doStuff() {
      for (int = 0; i < sizeOfStr; i++) {
        while (str->at[i] != '\n') {
          *anotherStr += str->at[i];
        }
        *arrayOfPointers[i] = *anotherStr->data();
        anotherStr = NULL; //reset this pointer
      }
    }
    
    int main() {
      doStuff();
      int sizeOfArray = sizeof(arrayOfPointers);
      for (int = 0; i < sizeOfArray; i++) {
        cout<< *arrayOfPointers[i] <<endl;
      }
      
      delete str;
      delete [] arrayOfPointers;
      delete anotherStr;
      return 0;
    
    }
    Would the output be:
    Yes, a string...
    Yes, another string...
    Yes, even another string...
    ?
    Last edited by Programmer_P; 05-20-2010 at 07:53 PM.

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    Programming Ninja In-T...
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    Bump.

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Programmer_P View Post
    Would the output be:
    Why are you asking us? Don't you have a computer of your own? Why not try it and see?

  8. #8
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    Quote Originally Posted by tabstop View Post
    Why are you asking us? Don't you have a computer of your own? Why not try it and see?
    For others' benefit.
    For the record, I tried it (though obviously including <string> and <iostream>), but it didn't compile. It said it expected constructor, destructor, or type conversion before the '=' token for the "string* str = NULL" line, as well as several lines after that. After changing the string pointer to a string object, it now says 'string' does not name a type, so obviously its not seeing the string class's definition for some reason, and I don't know why, seeing as I included it....
    I'm an alien from another world. Planet Earth is only my vacation home, and I'm not liking it.

  9. #9
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Programmer_P View Post
    For others' benefit.
    For the record, I tried it (though obviously including <string> and <iostream>), but it didn't compile. It said it expected constructor, destructor, or type conversion before the '=' token for the "string* str = NULL" line, as well as several lines after that. After changing the string pointer to a string object, it now says 'string' does not name a type, so obviously its not seeing the string class's definition for some reason, and I don't know why, seeing as I included it....
    The <string> header doesn't give you a type called string. It does, however, give you a type called std::string.

  10. #10
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    Quote Originally Posted by tabstop View Post
    The <string> header doesn't give you a type called string. It does, however, give you a type called std::string.
    Oh right..duh. I should have guessed that.
    Thanks.

    However, even after adding the line:

    Code:
    using namespace std;
    I still get the same errors about expecting constructor before '=' token.
    I'm an alien from another world. Planet Earth is only my vacation home, and I'm not liking it.

  11. #11
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Programmer_P View Post
    Oh right..duh. I should have guessed that.
    Thanks.

    However, even after adding the line:

    Code:
    using namespace std;
    I still get the same errors about expecting constructor before '=' token.
    The code you posted works perfectly fine:
    Code:
    #include <string>
    
    int main() {
        std::string *str = NULL;
        return 0;
    }
    is a marvelous piece of code that compiles with no errors.

  12. #12
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    Quote Originally Posted by tabstop View Post
    The code you posted works perfectly fine:
    Code:
    #include <string>
    
    int main() {
        std::string *str = NULL;
        return 0;
    }
    is a marvelous piece of code that compiles with no errors.
    Well, it didn't for me. Still, multiple errors.
    Evidently, my compiler doesn't seem to like when I try to create a "new" string outside any function.
    I'm an alien from another world. Planet Earth is only my vacation home, and I'm not liking it.

  13. #13
    Programming Ninja In-T...
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    Also note that the code was only an example anyway. In the real code that I was really asking about, all variables (including the ones that are created in dynamic memory) are created inside functions.
    I'm an alien from another world. Planet Earth is only my vacation home, and I'm not liking it.

  14. #14
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Programmer_P View Post
    Well, it didn't for me. Still, multiple errors.
    Evidently, my compiler doesn't seem to like when I try to create a "new" string outside any function.
    No ......... You can't do anything at all outside of a function.

  15. #15
    a_capitalist_story
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    Dude! The clumsiest "programming ninja" ever!

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