strcpy command

please explain strcpy command !!!!!!!!

is the following a valid function ??

Code:

---


char *strcpy (char *End, char *Begin)

{  char *s, *t;
   
    s = Begin;
    t = End;

    while (s = '\0')
 
      { t = s;
        *s++;
        *t++;
      }

      t = '\0';
      return t;
}

---

I am guessing this function is just copying string from BEGIN to END using the strcpy command but not sure of
1) if the while loop is correct
2) what the deal is with saying t = '\0' wouldn't the loop end automatically when *t pointed to the NULL character??
3) do you return t or 0 ???

there are a few code errors here.

Code:

---


char *strcpy (char *End, char *Begin)
{ 
    char *s, *t;
   
    s = Begin;
    t = End;

    while (*s != '\0')  // depending on the fact that there is a '\0' at the end of the string
    {
        *t = *s;
        s++;
        t++;
    }

    t = '\0';
    return t;
}

---

Should be *t = '\0'; at the end

doah thanks salem.

You handle the case where the strings are empty just fine. However if eitehr parameter is NULL, you're going to ahve problems.

so no-one's code is complete???

the code states that while *s is not pointing to the NULL
*s increments to next char in string and copies to t ??
when *s finally gets to the NULL loop stops there and *t is now NULL and then return t which in effect is s , right???

Quote:

---

Originally posted by Peachy
so no-one's code is complete???

the code states that while *s is not pointing to the NULL
*s increments to next char in string and copies to t ??
when *s finally gets to the NULL loop stops there and *t is now NULL and then return t which in effect is s , right???

---

Its not complete. If either pointer is null (NOT the data that is being pointed to), you will crash and burn.

Please I don't see the difference between an empty string
and NULL.

an empty string = a pointer to a null char '\0'

a null pointer = a pointer that points to memory address 0

And so I check for NULL by
also checking for 0

Code:

---


char *strcpy (char *End, char *Begin)
{ 
    char *s, *t;
   
    s = Begin;
    t = End;

    while (*s != '\0' || *s != 0)    // check for 0 and NULL here ???
    {
        *t = *s;
        s++;
        t++;
    }

    t = '\0';
    return t;
}

---

Code:

---

void foo ( char *s ) {
  if ( s == NULL ) return;
  ...
}
...
foo ( NULL );

---

The NULL pointer is a pointer to an unused (and unusable) memory location. On some operating systems, any attempt to dereference the NULL pointer will kill your program (basically, any use of *s within the function). You can only compare s to NULL, and take action as appropriate.
http://www.eskimo.com/~scs/C-faq/s5.html

Code:

---

void foo ( char *s ) {
  if ( s == NULL ) return;
  while ( *s != '\0' ) {
    ...
  }
  ...
}
...
foo ( "" );

---

The nul character has the value '\0', and is used to mark the end of all valid 'C' style strings. An empty string "" is a pointer to a single char, which contains the value '\0'.

So your strcpy function should do this first

Code:

---

if ( Begin == NULL || End == NULL ) return NULL;

---