strcpy anamoly, underfined behaviour

Question

#include<string.h>
int main()
{
     char *s;
     strcpy(s,"asdqw");
     strcpy(s,s+2);
     return 0;
}

This program is not showing up any error when run in linux system, it works fine. But when on running in mac osx, it is showing abort trap : 6. Why is this so happening so?

nalzok · Answer 1 · 2016-02-24T09:51:24.600

2

You have to allocate memory to s. Like this:

char *s = malloc(100);

Otherwise, undefined behaviour is caused. Since the behaviour is undefined, it working on Linux and not working on OS X are both reasonable.

Also, as @Florian Zwoch wisely points out, the second strcpy() operates on overlapping memory areas, which invokes undefined behaviour again. This is because strcpy() doesn't allow memory areas overlapping. You may want to use memmove(s, s + 2, sizeof (s + 2));, which allows the destination and source to overlap.

edited Feb 24 '16 at 09:51

answered Feb 24 '16 at 08:29

nalzok

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additionally the 2nd strcpy operates on overlapping memory areas. this behavior is undefined. – Florian Zwoch Feb 24 '16 at 09:30
The answer you said @sun is not a problem here, it still pops same erroe. – Aswin Prasad Feb 24 '16 at 09:36
[link](http://demin.ws/blog/english/2011/07/14/strcpy-on-overlapped-strings/) This clearly explains overlapping memory problem. – Aswin Prasad Feb 24 '16 at 09:59
@aswinmythili `malloc()` is not the only problem here. Both the lack of `malloc()` and the use of `strcpy()` are wrong. – nalzok Feb 24 '16 at 09:59

score 0 · Answer 2 · answered Feb 24 '16 at 08:31

0

You can run "Valgrind" on Linux and see if is there any error about memory.

Valgrind easy Tutorial This is an easy tutorial how to use it.

It's because it could be a memory problem.

answered Feb 24 '16 at 08:31

Fernando Sanchiz

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strcpy anamoly, underfined behaviour

2 Answers2