Thread: 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)

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.

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 -_-)

>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.

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

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!

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.