quick guide

This function copies the contents of one string into
another.The base address of the source and target strings
should be supplied to this function.Here is an example of
strcpy() in action.....

main()
{
char source[] = "sayonara";
char target[20];
strcpy(target, source);
printf("\n source string= %s", source);
printf("\n target string = %s", target);
}

output:
source string = sayonara
target string = sayonara
On supplying the base address , strcpy() goes on copying
the characters in source string into the target string till
it doesn't encounter the end of source string('\0'). It is
our responsibility to see to it that the target string's
dimension is big enough to hold the string being copied into
it. Thus , a string gets copied into another ,piece -meal ,
character by character . There is no short cut for this .

User-defined Function for strcpy():

main()
{
char source[] = "sayonara";
char target[20];
xstrcpy(target, source);
printf("\n source string= %s", source);
printf("\n target string = %s", target);
}
xstrcpy(char *t, char *s)
{
while (*s! = '\0')
{
*t = *s;
s++;
t++;
}
*t = '\0';
}

output:
source string = sayonara
target string = sayonara

Note that having copied the entire source string into the
target string ,it is necessary to place a '\0' into the
target string , to mark its end. If you look at the prototype
of strcpy() standard library function, it looks like this
strcpy(char *t, const char *s);
We didn't use the keyword constant in our version of
xstrcpy() and still our function worked correctly. So what is
the need of the const qualifier?what would happen if we add
the following lines beyond the last statement of xstrcpy()?
s = s-8;
*s = 'k';
This would change the source string to "Kayonara" . Can
we not ensure that the source string doesn't change even
accidentally in xstrcpy()? We can ,by changing the definition
as folows:
void xstrcpy (char *t,const char *s)
{
while(*s! ='\0')
{
*t = *s;
s++;
t++;
}
*t = '\0';
}

By declaring char *s as const we are declaring that the
source string should remain constant Thus the const qualifier
ensures that your program does not inadvertently alter a
variable that you intended to be a constant. It also reminds
anybody reading the program listing that the variable is not
intended to change