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digitalmars.D.bugs - 0.93 bug with dyn array returns?

reply 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
Jun 26 2004
parent reply 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
Jun 26 2004
parent 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;
Jun 27 2004