• Miles (16/16) Jun 26 2004 First post to digitalmars news... I'm really interested in D, but with a...
• Derek (8/26) Jun 26 2004 You are correct that it is returning a pointer to a stack entity. The
• Serge Semashko (13/39) Jun 27 2004 Right, it is expected to behave so, but it is very nonobvious and almost...

Miles <_______ _______.____> writes:

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

Derek <derek psyc.ward> writes:

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

Serge Semashko <serge lxnt.info> writes:

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;