动态缓冲库 [英] Dynamic buffer library
问题描述
我今天早上一起攻击了这个，这样我就可以将我的超出
空格代码从其余的逻辑中移开。我想在我的动态缓冲区上允许数组
语法，所以我手动创建了一个带有
malloc（）的结构，并明智地使用了void *指针。
我决定发布它，因为这样的东西是
UB的滋生地，而这个小组很擅长找到它。 （我有一个牙医类比
，但它没有用完。）
这是我的代码：
/ *开始。 * /
#include< stdlib.h>
#include< string.h>
void * create_buffer（ size_t size，size_t max）
{
/ *我们需要在实际缓冲区之前分配三个size_t来保存
*每个的大小item，最大项目数和实际
*项目数。我们这样做而不是使用结构，因此仍然可以在返回的结构上使用
*数组语法。 * /
size_t * tmp = malloc（（3 * sizeof * tmp）+（size * max））;
if（tmp！= NULL）
{
tmp [0] =大小; / *每件商品的尺寸* /
tmp [1] = max; / *最大项目数* /
tmp [2] = 0; / *实际项目数* /
}
return（tmp！= NULL）？ tmp + 3：NULL;
}
/ *这个函数会返回三个可能的东西：
* 1.普通用法，它将返回缓冲区的新的最大大小。
* 2.如果内存不足，它将返回0.
* 3.如果传递NULL ，它只会返回buf的最大大小。
*在第二种情况之后使用第三种情况来恢复丢失的大小信息。
*如果buf为NULL，坏事会发生。 * /
size_t append_item（void * buf，void * itm）
{
size_t * tmp =（size_t *）buf - 3;
size_t size = tmp [0];
size_t max = tmp [1];
size_t num = ++ tmp [2];
/ *特殊情况下的早期退货。 * /
if（itm == NULL）
返回num;
/ *如果我们没有足够的空间，尝试并获得更多。 * /
if（num == max）{
size_t * rtmp;
max * = 2;
while（！（rtmp = realloc（tmp，max））&&（max tmp [1]））
--max;
}
/ *如果我们现在有足够的空间，我们很好。否则，我们煮熟了。 * /
if（max num）{
memmove（buf，itm，size）;
返回num;
}否则返回0;
}
/ *结束。 * /
它在gcc中编译并设置了所有警告。
-
Andrew Poelstra< http ：//www.wpsoftware.net/projects>
要通过电子邮件与我联系，请在上述域名中使用apoelstra。
" Do BOTH结束了电缆需要插上电源吗？ -Anon。
I hacked this together this morning so that I could shift my out-of-
space code away from the rest of my logic. I wanted to allow array
syntax on my dynamic buffers, so I manually created a struct with
malloc() and judicious use of void* pointers.
I decided to post it because stuff like this is breeding ground for
UB, and this group is good at finding it. (I had a dentist analogy
for that, but it didn''t work out.)
Here''s my code:
/* Start. */
#include <stdlib.h>
#include <string.h>
void *create_buffer (size_t size, size_t max)
{
/* We need to allocate three size_t before the actual buffer to hold
* the size of each item, the maximum number of items, and the actual
* number of items. We do it this way instead of using a struct so that
* array syntax can still be used on the returned structure. */
size_t *tmp = malloc ( (3 * sizeof *tmp) + (size * max) );
if (tmp != NULL)
{
tmp[0] = size; /* Size of each item */
tmp[1] = max; /* Maximum # of items */
tmp[2] = 0; /* Actual # of items */
}
return (tmp != NULL) ? tmp + 3 : NULL;
}
/* This function will return three possible things:
* 1. On ordinary usage, it will return the new maximum size of the buffer.
* 2. If it runs out of memory, it will return 0.
* 3. If passed NULL, it will do nothing but return maximum size of buf.
* The third case is used after the second case to recover lost size info.
* If buf is NULL, Bad Things will happen. */
size_t append_item (void *buf, void *itm)
{
size_t *tmp = (size_t *) buf - 3;
size_t size = tmp[0];
size_t max = tmp[1];
size_t num = ++tmp[2];
/* Early return on special case. */
if (itm == NULL)
return num;
/* If we don''t have enough space, try and get some more. */
if (num == max) {
size_t *rtmp;
max *= 2;
while (!(rtmp = realloc (tmp, max)) && (max tmp[1]))
--max;
}
/* If we now have enough space, we''re good. Otherwise, we''re cooked. */
if (max num) {
memmove (buf, itm, size);
return num;
} else return 0;
}
/* End. */
It compiles in gcc with all warnings set.
--
Andrew Poelstra <http://www.wpsoftware.net/projects>
To reach me by email, use `apoelstra'' at the above domain.
"Do BOTH ends of the cable need to be plugged in?" -Anon.
推荐答案
Andrew Poelstra写道：
Andrew Poelstra wrote:
我今天早上一起入侵了这个这样我就可以将我的超出
空间代码从其余的逻辑中移开。我想在我的动态缓冲区上允许数组
语法，所以我手动创建了一个带有
malloc（）的结构，并明智地使用了void *指针。
我决定发布它，因为这样的东西是
UB的滋生地，而这个小组很擅长找到它。 （我有一个牙医类比
，但它没有用完。）
这是我的代码：
/ *开始。 * /
#include< stdlib.h>
#include< string.h>
void * create_buffer（ size_t size，size_t max）
{
/ *我们需要在实际缓冲区之前分配三个size_t来保存
*每个的大小item，最大项目数和实际
*项目数。我们这样做而不是使用结构，因此仍然可以在返回的结构上使用
*数组语法。 * /
size_t * tmp = malloc（（3 * sizeof * tmp）+（size * max））;
if（tmp！= NULL）
{
tmp [0] =大小; / *每件商品的尺寸* /
tmp [1] = max; / *最大项目数* /
tmp [2] = 0; / *实际项目数* /
}
return（tmp！= NULL）？ tmp + 3：NULL;
}
/ *这个函数会返回三个可能的东西：
* 1.普通用法，它将返回缓冲区的新的最大大小。
* 2.如果内存不足，它将返回0.
* 3.如果传递NULL ，它只会返回buf的最大大小。
*在第二种情况之后使用第三种情况来恢复丢失的大小信息。
*如果buf为NULL，坏事会发生。 * /
size_t append_item（void * buf，void * itm）
{
size_t * tmp =（size_t *）buf - 3;
size_t size = tmp [0];
size_t max = tmp [1];
size_t num = ++ tmp [2];
/ *特殊情况下的早期退货。 * /
如果（itm == NULL）
返回num;
I hacked this together this morning so that I could shift my out-of-
space code away from the rest of my logic. I wanted to allow array
syntax on my dynamic buffers, so I manually created a struct with
malloc() and judicious use of void* pointers.
I decided to post it because stuff like this is breeding ground for
UB, and this group is good at finding it. (I had a dentist analogy
for that, but it didn''t work out.)
Here''s my code:
/* Start. */
#include <stdlib.h>
#include <string.h>
void *create_buffer (size_t size, size_t max)
{
/* We need to allocate three size_t before the actual buffer to hold
* the size of each item, the maximum number of items, and the actual
* number of items. We do it this way instead of using a struct so that
* array syntax can still be used on the returned structure. */
size_t *tmp = malloc ( (3 * sizeof *tmp) + (size * max) );
if (tmp != NULL)
{
tmp[0] = size; /* Size of each item */
tmp[1] = max; /* Maximum # of items */
tmp[2] = 0; /* Actual # of items */
}
return (tmp != NULL) ? tmp + 3 : NULL;
}
/* This function will return three possible things:
* 1. On ordinary usage, it will return the new maximum size of the buffer.
* 2. If it runs out of memory, it will return 0.
* 3. If passed NULL, it will do nothing but return maximum size of buf.
* The third case is used after the second case to recover lost size info.
* If buf is NULL, Bad Things will happen. */
size_t append_item (void *buf, void *itm)
{
size_t *tmp = (size_t *) buf - 3;
size_t size = tmp[0];
size_t max = tmp[1];
size_t num = ++tmp[2];
/* Early return on special case. */
if (itm == NULL)
return num;
这不会返回缓冲区的最大大小。
This doesn''t return the maximum size of buffer.
>
/ *如果我们没有足够的空间，请尝试获得更多。 * /
if（num == max）{
size_t * rtmp;
max * = 2;
while（！（rtmp = realloc（tmp，max））&&（max tmp [1]））
--max;
}
/ *如果我们现在有足够的空间，我们很好。否则，我们煮熟了。 * /
if（max num）{
memmove（buf，itm，size）;
>
/* If we don''t have enough space, try and get some more. */
if (num == max) {
size_t *rtmp;
max *= 2;
while (!(rtmp = realloc (tmp, max)) && (max tmp[1]))
--max;
}
/* If we now have enough space, we''re good. Otherwise, we''re cooked. */
if (max num) {
memmove (buf, itm, size);
buf仍然指向旧的内存块。
无论如何你想要新项目
放在现有的之后，对吗？
buf still points to the old memory block.
And in any case you want the new item to
be placed after the already existing ones , right ?
返回num;
}否则返回0;
}
/ *结束。 * /
它在gcc中编译并设置了所有警告。
return num;
} else return 0;
}
/* End. */
It compiles in gcc with all warnings set.
>从代码中看来你的意图是存储
>From the code it seems that your intention is to store
"项目"从buf开始[3]。是物品类型
size_t？如果不是，你怎么知道buf [3]是否正确
对齐？
the "items" starting at buf[3]. Are the items of type
size_t ? If not how do you know that buf[3] is properly
aligned ?
Spiros Bousbouras写道：
Spiros Bousbouras wrote:
Andrew Poelstra写道：
Andrew Poelstra wrote:
它在gcc中编译并设置了所有警告。
It compiles in gcc with all warnings set.
从代码中看来，您的意图似乎是存储
From the code it seems that your intention is to store
项"从buf开始[3]。是物品类型
size_t？如果不是，你怎么知道buf [3]是否正确
对齐？
the "items" starting at buf[3]. Are the items of type
size_t ? If not how do you know that buf[3] is properly
aligned ?
好吧，谷歌的界面确实破了。行阅读
从代码中看来，你的意图是存储是由我写的
但Google在From之前添加了一个权利。 ！
它认为这是一个邮件文件！
我现在开始寻找不同的基于网络的界面
to usenet。
Ok , Google''s interface is indeed broken. The line reading
"From the code it seems that your intention is to store" was
written by me but Google added a right before "From" !
It thinks it''s a mail file !
I''ll now start searching for a different web based interface
to usenet.
" Spiros Bousbouras" < sp **** @ gmail.comwrites：
"Spiros Bousbouras" <sp****@gmail.comwrites:
>>从代码中看来你的意图似乎是商店
>>From the code it seems that your intention is to store
" items"从buf开始[3]。是物品类型
size_t？如果不是，你怎么知道buf [3]是否正确
对齐？
the "items" starting at buf[3]. Are the items of type
size_t ? If not how do you know that buf[3] is properly
aligned ?
这些项目可能不是size_t。我不知道他们是否正确对齐（这是UB的一个例子，我知道我错过了）。什么
对我来说是保证对齐的最佳方式？我要去
需要使用工会吗？
感谢您的评论：我已经更正了我的append_item功能
下面（大部分只是拼写错误和错过的行）：
/ *我们现在需要获取缓冲区的地址，因为realloc（）
*可能会改变指针的值。 * /
size_t append_item（void ** buf，void * itm）
{
size_t * tmp =（size_t *）* buf - 3;
size_t size = tmp [0];
size_t max = tmp [1];
size_t num = ++ tmp [2 ];
/ *特殊情况的早期回报。 * /
if（itm == NULL）
返回最大值;
/ *如果我们没有足够的空间，尝试并获得更多。 * /
if（num == max）{
size_t * rtmp;
max * = 2;
rtmp = realloc（tmp，max）;
while（（rtmp == NULL）&&（max tmp [1]））
rtmp = realloc（tmp， - max）;
}
/ *如果我们现在有足够的空间，我们很好。否则，我们煮熟了。 * /
if（max num）{
* buf = rtmp;
memmove（buf，itm，size）;
返回num;
}否则返回0;
}
-
Andrew Poelstra< http://www.wpsoftware.net/projects>
要通过电子邮件与我联系，请在上述域名中使用apoelstra。
" ;是否需要插入电缆的两端？ -Anon。
The items may not be of size_t. I don''t know that they''re properly
aligned (this is an example of the UB I knew that I missed). What
would be the best way for me to guarantee alignment? Am I going to
need to use a union?
Thanks for your comments: I''ve corrected my append_item function
below (most of it was just typos and missed lines):
/* We now need to get the address of the buffer, because realloc()
* may change the value of the pointer. */
size_t append_item (void **buf, void *itm)
{
size_t *tmp = (size_t *) *buf - 3;
size_t size = tmp[0];
size_t max = tmp[1];
size_t num = ++tmp[2];
/* Early return on special case. */
if (itm == NULL)
return max;
/* If we don''t have enough space, try and get some more. */
if (num == max) {
size_t *rtmp;
max *= 2;
rtmp = realloc (tmp, max);
while ((rtmp == NULL) && (max tmp[1]))
rtmp = realloc (tmp, --max);
}
/* If we now have enough space, we''re good. Otherwise, we''re cooked. */
if (max num) {
*buf = rtmp;
memmove (buf, itm, size);
return num;
} else return 0;
}
--
Andrew Poelstra <http://www.wpsoftware.net/projects>
To reach me by email, use `apoelstra'' at the above domain.
"Do BOTH ends of the cable need to be plugged in?" -Anon.
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