Programming Forums > Application Development > C

darthsabbath · May 23rd, 2006, 3:54 AM

I'm playing around with the classic K&R, and am in the chapter on Pointers. I'm having a bit of a problem with the strcopy() function listed... it keeps segfaulting whenever i compile and run the program. For those who don't have K&R, the code listed is:

(Toggle Plain Text)

/* Copies t to s */
void strcpy(char *s, char *t)
{
        while((*s = *t) != '\0') {
                s++;
                t++;
        }
}

The code I'm using to call the function is

(Toggle Plain Text)

main()
{
	char *p1; /* I've alternately tried pre-setting this to an equal length string to see if that would work... no joy */
	char *p2 = "Now is the time";
	strcpy(p1, p2);
}

The problem seems to be in the while((*s = *t) != '\0') loop. If I don't do the comparison between the two, I can manipulate the passed strings fine... i.e.

(Toggle Plain Text)

while(*t != '\0') {
	printf("%c\n", *t);
	s = t;
	t++;
	s++;
	printf("%c\n", *s);
	
}

I've also tried changing the while loop test to ((s = t) != '\0')... this results in the string being assigned properly... if I pipe out the contents of each char in the strings... I get

(Toggle Plain Text)

N N
o o
w w

i i
s s

t t
h h
e e

t t
i i
m m
e e
^@ ^@
% %
c c

% %
c c

It seems like it's going past the end of the string and into the realm of garbage.

I'm kinda lost, any pointers as to what I'm doing wrong (No pun intended)?

Thanks,
Phil

May 23rd, 2006, 3:54 AM	#1
darthsabbath Newbie Join Date: Dec 2005 Posts: 15 Rep Power: 0	Passing Pointers to Functions I'm playing around with the classic K&R, and am in the chapter on Pointers. I'm having a bit of a problem with the strcopy() function listed... it keeps segfaulting whenever i compile and run the program. For those who don't have K&R, the code listed is: (Toggle Plain Text) /* Copies t to s / void strcpy(char s, char t) { while((s = t) != '\0') { s++; t++; } } / Copies t to s / void strcpy(char s, char t) { while((s = t) != '\0') { s++; t++; } } The code I'm using to call the function is (Toggle Plain Text) main() { char p1; /* I've alternately tried pre-setting this to an equal length string to see if that would work... no joy / char p2 = "Now is the time"; strcpy(p1, p2); } main() { char p1; / I've alternately tried pre-setting this to an equal length string to see if that would work... no joy / char p2 = "Now is the time"; strcpy(p1, p2); } The problem seems to be in the while((s = t) != '\0') loop. If I don't do the comparison between the two, I can manipulate the passed strings fine... i.e. (Toggle Plain Text) while(t != '\0') { printf("%c\n", t); s = t; t++; s++; printf("%c\n", s); } while(t != '\0') { printf("%c\n", t); s = t; t++; s++; printf("%c\n", s); } I've also tried changing the while loop test to ((s = t) != '\0')... this results in the string being assigned properly... if I pipe out the contents of each char in the strings... I get (Toggle Plain Text) N N o o w w i i s s t t h h e e t t i i m m e e ^@ ^@ % % c c % % c c N N o o w w i i s s t t h h e e t t i i m m e e ^@ ^@ % % c c % % c c It seems like it's going past the end of the string and into the realm of garbage. I'm kinda lost, any pointers as to what I'm doing wrong (No pun intended)? Thanks, Phil

Thread Tools
Show Printable Version Email this Page
Display Modes
Switch to Linear Mode Switch to Hybrid Mode Threaded Mode

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Programming Forums > Application Development > C

Passing Pointers to Functions