First post to digitalmars news... I'm really interested in D, but with a few minutes of programming, I found something that may be a bug. If I do:

	char[] test() {
		char[5] res = "12345";
		return res;
	}
	char[] result = test();

result receives right number of elements, but with garbage in their place. If I printf result, even more garbage is generated in it. If I change res in test() to char[], it returns what is expected to.

Looks like `return res;´ is returning a char[] structure with the right length field, but with a data pointer pointing to the stack within test(), which is invalidated after the function returns.

Sorry if this is a known issue.

-- 
Miles

On Sat, 26 Jun 2004 19:15:58 -0300, Miles wrote:

> First post to digitalmars news... I'm really interested in D, but with a few minutes of programming, I found something that may be a bug. If I do:
> 
> 	char[] test() {
> 		char[5] res = "12345";
> 		return res;
> 	}
> 	char[] result = test();
> 
> result receives right number of elements, but with garbage in their place. If I printf result, even more garbage is generated in it. If I change res in test() to char[], it returns what is expected to.
> 
> Looks like `return res;´ is returning a char[] structure with the right length field, but with a data pointer pointing to the stack within test(), which is invalidated after the function returns.
> 
> Sorry if this is a known issue.

You are correct that it is returning a pointer to a stack entity. The 'solution' is to return a copy of that array...

   return res.dup;

BTW, this is how D is expected to behave.

-- 
Derek
Melbourne, Australia

Derek wrote:

>>First post to digitalmars news... I'm really interested in D, but with a few minutes of programming, I found something that may be a bug. If I do:
>>
>>	char[] test() {
>>		char[5] res = "12345";
>>		return res;
>>	}
>>	char[] result = test();
>>
>>result receives right number of elements, but with garbage in their place. If I printf result, even more garbage is generated in it. If I change res in test() to char[], it returns what is expected to.
>>
>>Looks like `return res;´ is returning a char[] structure with the right length field, but with a data pointer pointing to the stack within test(), which is invalidated after the function returns.
>>
>>Sorry if this is a known issue.
> 
> 
> You are correct that it is returning a pointer to a stack entity. The
> 'solution' is to return a copy of that array...
> 
>    return res.dup;
> 
> BTW, this is how D is expected to behave.

Right, it is expected to behave so, but it is very nonobvious and almost every newbee hits this problem. Can D compiler detect this situation as compile time error (array allocated on stack as a return value) or add some runtime checks that can help debugging this?

Another nonobvious thing that a newbee can hit is the use of local string as associative array index, just try the following:

	char[] i;
	int[char[]] dict;
	i = "abc";
	dict[i] = 1;
	i = "def";
	dict[i] = 2;