| ??? 05/26/05 13:22 Read: times |
#93928 - That's the problem Responding to: ???'s previous message |
Andy Neil said:
Donald Catto said:
"Neil's point is that, although pointers & arrays are different, they both use the same Notation."
No. He states that "pointer notation and array notation are interchangeable". He does not state that "[pointers and arrays] use the same notation", which is even less correct, if it is possible to have a state of 'less correct'. By "Notation," I'm thinking of: The value of an array name is the address of the start of the array; The value of a pointer is the address of the start of the pointed-to object. The index-offset operator [] may be applied to a pointer as well as an array name. The dereference operator * may be applied to an array name as well as a pointer. void main( void ) { char my_array[] = "Array"; char *my_pointer = "Pointer"; char my_char; my_char = my_array[0]; my_char = my_pointer[0]; my_char = *my_array; my_char = *my_pointer; } The differences lie in the behaviour: Defining an array allocates storage for the array elements. You cannot assign to an array name. Let's expand on your example a bit:
void main( void )
{
char my_array[] = "Array";
char *my_pointer = "Pointer";
char my_char;
my_char = my_array[0];
my_char = my_pointer[0];
my_char = *my_array;
my_char = *my_pointer;
*my_array='X';
*my_pointer='X'; //Uh oh!
my_array[0]='X';
my_pointer[0]='X'; //Uh oh!
my_pointer=my_array;
*my_pointer='X'; //Ok now!
my_pointer[0]='X'; //Ok now!
printf("%dn",(int)sizeof(my_array));
printf("%dn",(int)sizeof(my_pointer)); //Different!
&my_array; //Pointer to array of char
&my_pointer; //Pointer to pointer to char
}
I hope this serves to illustrate why is it so dangerous to think that arrays and pointers are interchangeable, or that similarity of notation implies similarity of results. |
| Topic | Author | Date |
| Unions in C | 01/01/70 00:00 | |
| You miss the point completely... | 01/01/70 00:00 | |
| Easy with Union | 01/01/70 00:00 | |
| You can see from the Raghu example... | 01/01/70 00:00 | |
| Platform-dependence | 01/01/70 00:00 | |
| Padding in unions | 01/01/70 00:00 | |
| portability | 01/01/70 00:00 | |
| array=pointer...? | 01/01/70 00:00 | |
| array != pointer | 01/01/70 00:00 | |
| Quirk of C | 01/01/70 00:00 | |
| Read the FAQ | 01/01/70 00:00 | |
| Read the Comment | 01/01/70 00:00 | |
| Read everything | 01/01/70 00:00 | |
| Looks the same to me | 01/01/70 00:00 | |
| This One | 01/01/70 00:00 | |
| That's the problem | 01/01/70 00:00 | |
| Good example | 01/01/70 00:00 | |
| No fun | 01/01/70 00:00 | |
| Well... | 01/01/70 00:00 | |
| Of course it does! | 01/01/70 00:00 | |
| Hmm | 01/01/70 00:00 | |
| Actually, even less. | 01/01/70 00:00 | |
| const pointer | 01/01/70 00:00 | |
| O.K you win | 01/01/70 00:00 | |
| Please conclude | 01/01/70 00:00 | |
| Not Exactly | 01/01/70 00:00 | |
End of wrong stick? | 01/01/70 00:00 |