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digitalmars.D.bugs - compiler does not complain no required return value

reply z gg.com writes:
Instead, the generated binary will abort at run-time and give misleading
message:


int f() {
return 0;  // gdc Error: AssertError Failure rtn.d(3); dmd Aborted
}

int main(char[][] args) {
f();
return 0;
}
Aug 26 2005
next sibling parent z gg.com writes:
int f() {
  // return 0;  // gdc Error: AssertError Failure rtn.d(3); dmd Aborted


---^^

need to comment out line 3, to see the error.


}

int main(char[][] args) {
f();
return 0;
}
Aug 26 2005
prev sibling parent reply Derek Parnell <derek psych.ward> writes:
On Fri, 26 Aug 2005 07:18:51 +0000 (UTC), z gg.com wrote:


 Instead, the generated binary will abort at run-time and give misleading
 message:
 
 int f() {
 return 0;  // gdc Error: AssertError Failure rtn.d(3); dmd Aborted
 }
 
 int main(char[][] args) {
 f();
 return 0;
 }


This is not a bug. 

If you define a routine to return a value, but you don't actually return
anything, the function will crash at run time. The compiler does not
attempt to detect this situation, instead it generates a hidden assert at
the end of the function.

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
26/08/2005 6:04:14 PM
Aug 26 2005
next sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Derek Parnell wrote:

 On Fri, 26 Aug 2005 07:18:51 +0000 (UTC), z gg.com wrote:
 

 Instead, the generated binary will abort at run-time and give misleading
 message:

 int f() {




[implemented correction]

 // return 0;  // gdc Error: AssertError Failure rtn.d(3); dmd Aborted
 }

 int main(char[][] args) {
 f();
 return 0;
 }


 
 This is not a bug. 


Nonsense.

http://www.digitalmars.com/d/statement.html#return

"At least one return statement is required if the function specifies a
return type that is not void."

Stewart.

-- 
-----BEGIN GEEK CODE BLOCK-----
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GCS/M d- s:- a->--- UB  P+ L E  W++  N+++ o K- w++  O? M V? PS- PE- Y? 
PGP- t- 5? X? R b DI? D G e++>++++ h-- r-- !y
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My e-mail is valid but not my primary mailbox.  Please keep replies on 
the 'group where everyone may benefit.
Aug 26 2005
parent reply Derek Parnell <derek psych.ward> writes:
On Fri, 26 Aug 2005 12:09:41 +0100, Stewart Gordon wrote:


 Derek Parnell wrote:

 On Fri, 26 Aug 2005 07:18:51 +0000 (UTC), z gg.com wrote:
 

 Instead, the generated binary will abort at run-time and give misleading
 message:

 int f() {




 [implemented correction]

 // return 0;  // gdc Error: AssertError Failure rtn.d(3); dmd Aborted
 }

 int main(char[][] args) {
 f();
 return 0;
 }


 
 This is not a bug. 


 
 Nonsense.
 
 http://www.digitalmars.com/d/statement.html#return
 
 "At least one return statement is required if the function specifies a
 return type that is not void."


But 'required' by what? I suspect it is the run-time application that
requires it rather than the compiler itself.

-- 
Derek Parnell
Melbourne, Australia
27/08/2005 12:27:36 AM
Aug 26 2005
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Derek Parnell wrote:

 On Fri, 26 Aug 2005 12:09:41 +0100, Stewart Gordon wrote:


<snip>

 http://www.digitalmars.com/d/statement.html#return

 "At least one return statement is required if the function specifies a
 return type that is not void."


 
 But 'required' by what?


The D language.  And hence any correct D compiler.


 I suspect it is the run-time application that
 requires it rather than the compiler itself.


If that's so, then you could equally state that

"The body of all asserts is required to evaluate to non-zero."

By which the average person is likely to interpret what?

Stewart.

-- 
-----BEGIN GEEK CODE BLOCK-----
Version: 3.1
GCS/M d- s:- a->--- UB  P+ L E  W++  N+++ o K- w++  O? M V? PS- PE- Y? 
PGP- t- 5? X? R b DI? D G e++>++++ h-- r-- !y
------END GEEK CODE BLOCK------

My e-mail is valid but not my primary mailbox.  Please keep replies on 
the 'group where everyone may benefit.
Aug 26 2005
parent Dave <Dave_member pathlink.com> writes:
In article <dengj7$1is0$1 digitaldaemon.com>, Stewart Gordon says...

Derek Parnell wrote:

 On Fri, 26 Aug 2005 12:09:41 +0100, Stewart Gordon wrote:


<snip>

 http://www.digitalmars.com/d/statement.html#return

 "At least one return statement is required if the function specifies a
 return type that is not void."


 
 But 'required' by what?


The D language.  And hence any correct D compiler.


 I suspect it is the run-time application that
 requires it rather than the compiler itself.


If that's so, then you could equally state that

"The body of all asserts is required to evaluate to non-zero."


As long as your not talking about the compiler checking every possible path for
a return statement (something that probably no compiler has ever gotten 100%
right anyhow), then I would have to agree that the compiler should at least
check for a return statement inside the body of a function.

Take a look in the archives - IMO, Walter has good reasoning for the compiler
not forcing a return for all paths. But checking that a function actually has a
valid return statement if it's expected to return something should be part of
the reference compiler because 1) it will save programmers a lot of "oopses", 2)
it's gotta be readily do-able to verify 100% of the time and 3) the spec. above
really is unequivocal on the matter.

- Dave



By which the average person is likely to interpret what?

Stewart.

-- 
-----BEGIN GEEK CODE BLOCK-----
Version: 3.1
GCS/M d- s:- a->--- UB  P+ L E  W++  N+++ o K- w++  O? M V? PS- PE- Y? 
PGP- t- 5? X? R b DI? D G e++>++++ h-- r-- !y
------END GEEK CODE BLOCK------

My e-mail is valid but not my primary mailbox.  Please keep replies on 
the 'group where everyone may benefit.
Aug 26 2005
prev sibling parent reply z gg.com writes:
 return 0;  // gdc Error: AssertError Failure rtn.d(3); dmd Aborted





The compiler does not
attempt to detect this situation, instead it generates a hidden assert at
the end of the function.


*EVEN* in that case, a more meaningfull message should be generated, e.g.

"NoReturnValueAssertError"

Which is much more human readable.
Aug 26 2005
parent Mike Parker <aldacron71 yahoo.com> writes:
z gg.com wrote:

return 0;  // gdc Error: AssertError Failure rtn.d(3); dmd Aborted







 *EVEN* in that case, a more meaningfull message should be generated, e.g.
 
 "NoReturnValueAssertError"
 
 Which is much more human readable.
 
 
 


When you compile with -w the compiler will let you know of missing 
return statements:


end of function.

Walter added this as a concession after much debate over the default 
behaviour. So if you want to catch these cases at compile time, use -w 
and be happy.
Aug 26 2005