Very stupid question involving pointers

This is a discussion on Very stupid question involving pointers within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> #include <stdlib.h> typedef struct { char* Name; char* Desc; //bool* Comp; }quest; int main(int argc, char *argv[]) ...

  1. #1
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    Very stupid question involving pointers

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    typedef struct
    {
        char* Name;
        char* Desc;
        //bool* Comp;
    }quest;
    int main(int argc, char *argv[])
    {
      quest *QOne;
      QOne->Name = "Number One";
      printf(QOne->Name);
      quest *QTwo;
      QTwo->Name = "Number Two";
      printf(QOne->Name,"\n",QTwo->Name);
      system("PAUSE");	
      return 0;
    }
    Everytime I run it crashes at the very start up. Can somebody explain why it does this? Almost everytime I use pointers, the program always crashes. Can somebody explain why it does this?
    (Note: I have read the tutorials)
    To code is divine

  2. #2
    Gawking at stupidity
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    When you declare QOne, it contains random data. Then you deference it when it's pointing to that invalid memory address. To solve your problem you should allocate some memory and make QOne point to it. Same goes with QTwo.
    If you understand what you're doing, you're not learning anything.

  3. #3
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    So...why create a pointer...ever? If you’re just referencing an existing variable, what advantages does it serve? Besides allowing for quicker functions, what real purpose does it serve???

    (This thread is making me feel so dumb -_-)
    To code is divine

  4. #4
    Code Goddess Prelude's Avatar
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    >If you’re just referencing an existing variable, what advantages does it serve?
    Two words: Anonymous memory. Pointers allow you to reference memory without declaring variables first:
    Code:
    double *p = malloc ( sizeof ( double ) );
    Pointers allow you to easily create complex dynamic data structures. Without pointers you would be forced to use array indices, and that's not exactly a pleasant experience.

    >So...why create a pointer...ever?
    If you know how they work, and how to use them, you'll eventually discover the answer to this question on your own.
    My best code is written with the delete key.

  5. #5
    Registered User
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    its usefull when you dealing with arrays, since a function cant return an array, you use a pointer to access any element in the array
    When no one helps you out. Call google();

  6. #6
    C(++)(#)
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    Quote Originally Posted by Prelude
    >If you’re just referencing an existing variable, what advantages does it serve?
    Two words: Anonymous memory. Pointers allow you to reference memory without declaring variables first:
    Code:
    double *p = malloc ( sizeof ( double ) );
    Pointers allow you to easily create complex dynamic data structures. Without pointers you would be forced to use array indices, and that's not exactly a pleasant experience.

    >So...why create a pointer...ever?
    If you know how they work, and how to use them, you'll eventually discover the answer to this question on your own.
    Ooooh thanks Prelude, I didn't know about that!

    And also, thanks to InvariantLoop for helping me with this!
    To code is divine

  7. #7
    ATH0 quzah's Avatar
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    Ooooo fun with pointers.
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main( void )
    {
        const char *specifier[] = { "%c", "%d", "%f", "%s" };
        size_t size[] = { 1, sizeof( int ), sizeof( float ), BUFSIZ };
        int x;
        void *data = NULL;
    
        printf(
            "1) Read a single character.\n"
            "2) Read a single integer.\n"
            "3) Read a floating point number.\n"
            "4) Readin a string.\n\n"
            "Your choice: "
        );
    
    
        x = getchar();
        if( x < '1' || x > '4' )
            return !!printf( "Next time try following the rules.\n" );
    
        x -= '1';
    
        while( getchar() != '\n' );
    
        if( (data = malloc( size[ x ] )) )
        {            
            printf( "Enter your data now: " );
            fflush( stdout );
    
            if( scanf( specifier[ x ], data ) == 1 )
            {
                printf( "You entered \'" );
                switch( x )
                {
                    case 0: printf( specifier[ x ], *((char*)data) ); break;
                    case 1: printf( specifier[ x ], *((int*)data) ); break;
                    case 2: printf( specifier[ x ], *((float*)data) ); break;
                    case 3: printf( specifier[ x ], (char*)data ); break;
                }
                printf( "\'!\n" );
            }
            free( data );
        }
    
        return 0;
    }
    There's a fun example.

    Quzah.
    Hope is the first step on the road to disappointment.

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