Re: Null src pointer in memcpy?

[Martin Sebor]

Eric Lemings wrote:
 
I was just asking because I observed such a call in _rw_bufcat().

It happens when the printf-like functions in tests/src/printf.cpp
are creating a new buffer for formatting operations.


Fix it :)



Brad.


-Original Message-
From: Martin Sebor [mailto:[EMAIL PROTECTED] On Behalf Of Martin Sebor
Sent: Thursday, April 10, 2008 7:40 PM
To: dev@stdcxx.apache.org
Subject: Re: Null src pointer in memcpy?

This is explicitly required in 7.1.4 of C99:

   7.1.4 Use of library functions

   -1- Each of the following statements applies unless 
explicitly stated
   otherwise in the detailed descriptions that follow: If 
an argument

   to a function has an invalid value (such as a value outside the
   domain of the function, or a pointer outside the address space
   of the program, or a null pointer, or a pointer to 
non-modifiable
   storage when the corresponding parameter is not 
const-qualified)

   or a type (after promotion) not expected by a function with
   variable number of arguments, the behavior is undefined. ...

Here's an answer to the same question on comp.lang.c.moderated:
   http://tinyurl.com/6eqo3n

Martin Sebor wrote:

Eric Lemings wrote:
 
Is it safe to pass a null pointer as the 2nd argument to 

memcpy()?  Or

undefined?

Assuming the third argument is 0. Strictly speaking I believe it's
undefined because memcpy(s1, s2, n) is specified to copy n bytes
from the object pointed to by s2 into the object pointed to by s1
and a null pointer doesn't point to an object. An object is defined
as a region of storage in the execution environment, the contents
of which can represent values.

AFAIK, most implementations allow null pointers for no-op calls to
memcpy() but gcc issues a warning when it detects at compile time
that a null pointer is passed as the first or second argument to
memcpy().

Martin

RE: Null src pointer in memcpy?

[Eric Lemings]

 
I was just asking because I observed such a call in _rw_bufcat().
It happens when the printf-like functions in tests/src/printf.cpp
are creating a new buffer for formatting operations.

Brad.

 -Original Message-
 From: Martin Sebor [mailto:[EMAIL PROTECTED] On Behalf Of Martin Sebor
 Sent: Thursday, April 10, 2008 7:40 PM
 To: dev@stdcxx.apache.org
 Subject: Re: Null src pointer in memcpy?
 
 This is explicitly required in 7.1.4 of C99:
 
7.1.4 Use of library functions
 
-1- Each of the following statements applies unless 
 explicitly stated
otherwise in the detailed descriptions that follow: If 
 an argument
to a function has an invalid value (such as a value outside the
domain of the function, or a pointer outside the address space
of the program, or a null pointer, or a pointer to 
 non-modifiable
storage when the corresponding parameter is not 
 const-qualified)
or a type (after promotion) not expected by a function with
variable number of arguments, the behavior is undefined. ...
 
 Here's an answer to the same question on comp.lang.c.moderated:
http://tinyurl.com/6eqo3n
 
 Martin Sebor wrote:
  Eric Lemings wrote:
   
  Is it safe to pass a null pointer as the 2nd argument to 
 memcpy()?  Or
  undefined?
  
  Assuming the third argument is 0. Strictly speaking I believe it's
  undefined because memcpy(s1, s2, n) is specified to copy n bytes
  from the object pointed to by s2 into the object pointed to by s1
  and a null pointer doesn't point to an object. An object is defined
  as a region of storage in the execution environment, the contents
  of which can represent values.
  
  AFAIK, most implementations allow null pointers for no-op calls to
  memcpy() but gcc issues a warning when it detects at compile time
  that a null pointer is passed as the first or second argument to
  memcpy().
  
  Martin
  
 
 

Null src pointer in memcpy?

[Eric Lemings]

 
Is it safe to pass a null pointer as the 2nd argument to memcpy()?  Or
undefined?
 
Brad.
 

RE: Null src pointer in memcpy?

[Travis Vitek]

-Original Message-
From: Eric Lemings [mailto:[EMAIL PROTECTED] 
Sent: Thursday, April 10, 2008 5:42 PM
To: dev@stdcxx.apache.org
Subject: Null src pointer in memcpy?

 
Is it safe to pass a null pointer as the 2nd argument to memcpy()?  Or
undefined?


The function is documented to copy n bytes from s2 into s1. If n is
non-zero, then it must attempt to copy that many bytes from s2. So it is
safe only when the third parameter is 0.

Brad.
 

Re: Null src pointer in memcpy?

[Martin Sebor]

Eric Lemings wrote:
 
Is it safe to pass a null pointer as the 2nd argument to memcpy()?  Or

undefined?


Assuming the third argument is 0. Strictly speaking I believe it's
undefined because memcpy(s1, s2, n) is specified to copy n bytes
from the object pointed to by s2 into the object pointed to by s1
and a null pointer doesn't point to an object. An object is defined
as a region of storage in the execution environment, the contents
of which can represent values.

AFAIK, most implementations allow null pointers for no-op calls to
memcpy() but gcc issues a warning when it detects at compile time
that a null pointer is passed as the first or second argument to
memcpy().

Martin

Re: Null src pointer in memcpy?

[Martin Sebor]

This is explicitly required in 7.1.4 of C99:

  7.1.4 Use of library functions

  -1- Each of the following statements applies unless explicitly stated
  otherwise in the detailed descriptions that follow: If an argument
  to a function has an invalid value (such as a value outside the
  domain of the function, or a pointer outside the address space
  of the program, or a null pointer, or a pointer to non-modifiable
  storage when the corresponding parameter is not const-qualified)
  or a type (after promotion) not expected by a function with
  variable number of arguments, the behavior is undefined. ...

Here's an answer to the same question on comp.lang.c.moderated:
  http://tinyurl.com/6eqo3n

Martin Sebor wrote:

Eric Lemings wrote:
 
Is it safe to pass a null pointer as the 2nd argument to memcpy()?  Or

undefined?


Assuming the third argument is 0. Strictly speaking I believe it's
undefined because memcpy(s1, s2, n) is specified to copy n bytes
from the object pointed to by s2 into the object pointed to by s1
and a null pointer doesn't point to an object. An object is defined
as a region of storage in the execution environment, the contents
of which can represent values.

AFAIK, most implementations allow null pointers for no-op calls to
memcpy() but gcc issues a warning when it detects at compile time
that a null pointer is passed as the first or second argument to
memcpy().

Martin