释放指针有多精致？ [英] Just how delicate are freed pointers?
问题描述
以下代码是否安全？
SomeType * a，* b;
/ *部分代码.... * /
免费（一）;
if（a == b）b = NULL;
a = NULL;
谢谢。
-
David Scarlett
dscarlett @ _ _ _ _ _ _ _
_ _ _ _ _ optusnet.com.au
David Scarlett写道：
以下代码是否安全？
No.
SomeType * a，* b;
/ *部分代码.... * /
免费（a）;
if（a == b）b = NULL;
a = NULL;
SomeType * a，* b;
/ *有些代码...... * /
if（ a == b）b = NULL;
免费（a）;
a = NULL;
-
pete
On Sun，2004年5月16日03:25:21 GMT，pete< pf **** *@mindspring.com>写道：
David Scarlett写道：
以下代码是否安全？
否。
嗯。假设a在free（）之前有效且b仍然在比较的
点，我不明白为什么你认为这是不安全的。
个人在它之后测试指针的值似乎很奇怪
已被释放（并且你的版本在这个意义上更为传统），
但是因为我们是只测试/ pointer /而不是试图访问
它指向的内存，为什么OP的代码不是安全？
-leor
SomeType * a，* b;
/ *有些代码.... * /
免费（ a）;
if（a == b）b = NULL;
a = NULL;
SomeType * a， * b;
/ *有些代码.... * /
if（a == b）b = NULL;
免费（ a）;
a = NULL;
David Scarlett写道：
以下代码是否安全？
No.
SomeType * a，* b;
/ *部分代码.... * /
免费（a）;
该标准未规定是否更改了。它可能仍然
包含相同的值，它可能设置为NULL，或者它可能是一些
其他该死的值。
if（a == b）b = NULL;
相当无比的比较，对吧？
a = NULL;
谢谢。
Is the following code safe?
SomeType *a, *b;
/* Some code.... */
free(a);
if ( a == b ) b = NULL;
a = NULL;
Thanks.
--
David Scarlett
dscarlett@_ _ _ _ _ _ _ _
_ _ _ _ _ optusnet.com.au
David Scarlett wrote:
Is the following code safe?
No.
SomeType *a, *b;
/* Some code.... */
free(a);
if ( a == b ) b = NULL;
a = NULL;
SomeType *a, *b;
/* Some code.... */
if ( a == b ) b = NULL;
free(a);
a = NULL;
--
pete
On Sun, 16 May 2004 03:25:21 GMT, pete <pf*****@mindspring.com> wrote:
David Scarlett wrote:
Is the following code safe?
No.
Hmmm. Assuming a was valid before the free() and b still is at the
point of the comparison, I don''t get why you think this is unsafe.
Personally, it seems strange to test the value of a pointer after it
has been freed (and your version is more conventional in that sense),
but since we''re only testing the /pointer/ and not trying to access
the memory it is pointing to, why wouldn''t the OP''s code be "safe"?
-leor
SomeType *a, *b;
/* Some code.... */
free(a);
if ( a == b ) b = NULL;
a = NULL;
SomeType *a, *b;
/* Some code.... */
if ( a == b ) b = NULL;
free(a);
a = NULL;
David Scarlett wrote:
Is the following code safe?
No.
SomeType *a, *b;
/* Some code.... */
free(a);
The standard does not specify whether a is changed. It might still
contain the same value, it might be set to NULL, or it might be some
other damn value.
if ( a == b ) b = NULL;
Pretty pointless comparison, huh?
a = NULL;
Thanks.
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