is it legal to pass an address adjusted char pointer, to strcpy as its second arguement? as in:
strcpy (end, a_line + beginning_length)
I want the end of the string to copy from the beginning length to the null sentinal of a_line. Both end and a_line are char pointers.
Absolutely!
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thanks, thats what i thought
while were on the topic, is this legal:
If I'm correct in assuming most strcpy implementations simply do something like:Code:strcpy(str, str+1)
I'd think it would be safe, though the man page doesn't really go into much about the behaviour of editing strings concurrently in the str functions.Code:while((*dest++ = *src++) != '\0')
Last edited by @nthony; 08-26-2007 at 09:51 PM. Reason: (dest, src)
Does the man page mention anything about the fact that the strings may not overlap?
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
That's exactly why it WON'T work. If strcpy() is implemented as you describe (and it usually is), the result is an infinite loop that eventually crashes.Originally Posted by @nthony
woops, indeed it does, I must have been thinking of another man page. Yep, it clearly says undefined behaviour:
nm, I guess I was thinking of something else, I'll post again if I remember the function, I just remember the arguments were overlapping strings.If copying takes place between objects that overlap, the behavior is undefined...
Character movement is performed differently in different implementations. Thus, overlapping moves may yield surprises.
This issue is aligned with the ISO C standard; this does not affect compatibility with XPG3 applications. Reliable error detection by this function was never guaranteed.
p.s. I wonder what MingW's implementation is for this, because I think I've gotten away with this numerous times in the past.
edit: sorry brewbuck, I meant "strcpy(str, str+1)", backward src/dest args in C get me all the time... :S
Last edited by @nthony; 08-26-2007 at 09:52 PM.
memmove?
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
It's not backwards. Remember it this way:
Code:a = b; /* The data flows leftward */ strcpy(dst, src); /* Again, the data flows leftward. */
memmove() works fine for overlapping regions. It's memcpy() which can't be trusted.
