K&R's strcpy function - problem with pointers

[jamadagni]

s and t are the pointers whereas *s and *t are the values.(Remember * gives you the value).

So when strcpy(a,b) is executed, the values of a and b are passed to the function, and the function matches its argument declaration (char *s, char *t) to (a, b), so s and t are those pointers whose values (extracted by *) are those passed from a and b.

All right, now that's clear, but now how does s[i] = t[i] work in the first example? The pointer is not an array, right? So how can t[i] be a valid expression let alone get assigned to s[i]? If it were *s[i] = *t[i] it would be understandable...

[jacek]

The pointer is not an array, right?

That's the problem with arrays in C and C++ --- you can treat them as pointers to first element.

In fact x[i] is the same as *(x + i).

Maybe this will shed some light:
http://www.eskimo.com/~scs/cclass/notes/sx10b.html

[jamadagni]

In fact x[i] is the same as *(x + i).

But only if x is a pointer, right? For example, this will not be true: if char s[]="hello"; then s[3] = *(s + 3) -- correct?

[jacek]

For example, this will not be true: if char s[]="hello"; then s[3] = *(s + 3) -- correct?

No, s is also a pointer. This inconsistency is a real problem in C and C++.

#include <stdio.h>
 
int main()
{
   char s[] = "hello";
 
   printf( "%c\n", s[3] );
   printf( "%c\n", *(s+3) );
 
   return 0;
}

#include <stdio.h>

int main()
{
   char s[] = "hello";

   printf( "%c\n", s[3] );
   printf( "%c\n", *(s+3) );

   return 0;
}

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[jamadagni]

No, s is also a pointer. This inconsistency is a real problem in C and C++.

Why you call this an inconsistency? Just now I read in K&R:

By definition the value of a variable or expression of type array is the address of element zero of the array. Thus after the assignment pa = &a[0]; pa and a have identical values. Since the name of an array is a synonym for the location of the initial element, the assignment pa = &a[0]; can also be written as pa = a;

[jacek]

Why you call this an inconsistency?

Don't you feel confused when you learn how arrays work in C? Compare arrays from C with those in Pascal or Java.

Just now I read in K&R:

You know, they wouldn't write something like "arrays are more a hack than a real data type".