省略号函数中动态分配的问题 [英] problems with dynamic allocation in an ellipses function

问题描述

大家好。


我是C的新手，所以请提前接受我的道歉:-)


我'我试图在while循环中为一个指向字符串的指针数组分配空间

（它们被接受为省略号），并且在

分配之后，当我断言"分配，断言失败!!!


void printStrings（s1，...）{//省略函数

....

....

void * myList;

int count = 1;

char * pArr = s1;

va_start（myList，s1）;

while（myList）{

pArr =（char *）realloc（pArr，++ count * sizeoff（ char *））;

断言（pArr）;

pArr [count-1] = va_arg（myList，char *）;

}


但是，如果我从

中取出2行的分配和断言，那么它可以工作!!!

ie - 以下是好的：


void * myList;

int count = 1;

char * pArr = s1 ;

va_start（myList，s1）;


pArr =（char *）realloc（pArr，++ count * sizeoff（char *））;

断言（pArr）; //这没关系


即使我将这两行放在一个只运行一次的for循环中，它也会失败！

失败!!!


int count = 1;

char * pArr = s1;

va_start（myList，s1）;

for（i = 0; i< 1; i ++）{// LOOP RUNS JUST ONCE

pArr =（char *）realloc（pArr，++ count * sizeoff（char *））;

断言（pArr）; // ASSERTION FAILS HERE !!!

}


我做错了什么以及为什么分配失败在

内while / for循环


非常感谢

Shiron

Hello all

I''m pretty new to C, so please accept my apologies in advance :-)

I''m trying to allocate space for an array of pointers to strings
(which are accepted as ellipses) inside a while loop, and after the
allocation, when i "assert" the allocation, the assertion fails!!!

void printStrings(s1, ...){ //ellipses function
....
....
void *myList;
int count=1;
char *pArr=s1;
va_start(myList, s1);
while( myList ){
pArr = (char *) realloc(pArr, ++count * sizeoff(char*));
assert(pArr);
pArr[count-1] = va_arg(myList, char*);
}

However, if i take the 2 lines of the allocation and assertion out of
he while, it works!!!
i.e. - the following is OK :

void *myList;
int count=1;
char *pArr=s1;
va_start(myList, s1);

pArr = (char *) realloc(pArr, ++count * sizeoff(char*));
assert(pArr); //THIS IS OK

even if i put these two lines in a for loop that run just once, it
fails!!!

int count=1;
char *pArr=s1;
va_start(myList, s1);
for(i =0; i <1; i++){ // LOOP RUNS JUST ONCE
pArr = (char *) realloc(pArr, ++count * sizeoff(char*));
assert(pArr); //ASSERTION FAILS HERE!!!
}

what Am i doing wrong and why is the allocation failing inside the
while/for loops

Thanks a lot
Shiron

推荐答案

hyperboogie说：

hyperboogie said:

Hello all


我是C的新手，所以请接受我的道歉提前:-)


我正在尝试为一串指向字符串的数组分配空间

（可以被接受为省略号）循环，并且在

分配之后，当我断言时分配，断言失败!!!


void printStrings（s1，...）{//省略函数

...

...

void * myList;

int count = 1;

char * pArr = s1;

va_start（myList，s1）;

while（myList）{

pArr =（char *）realloc（pArr，++ count * sizeoff（char *） ））;

Hello all

I''m pretty new to C, so please accept my apologies in advance :-)

I''m trying to allocate space for an array of pointers to strings
(which are accepted as ellipses) inside a while loop, and after the
allocation, when i "assert" the allocation, the assertion fails!!!

void printStrings(s1, ...){ //ellipses function
...
...
void *myList;
int count=1;
char *pArr=s1;
va_start(myList, s1);
while( myList ){
pArr = (char *) realloc(pArr, ++count * sizeoff(char*));

确保你的源文件顶部有＃include< stdlib.hnear，

输掉演员，使用temp，并获得正确的大小：


char * tmp = realloc（pArr，++ count * sizeof * pArr）;

if（tmp！= NULL）

{

pArr = tmp;

Make sure you have #include <stdlib.hnear the top of your source file,
lose the cast, use a temp, and get sizeof right:

char *tmp = realloc(pArr, ++count * sizeof *pArr);
if(tmp != NULL)
{
pArr = tmp;

assert（pArr）;

assert(pArr);

在C90中，断言需要一个整数表达式：


断言（pArr！= NULL）;


但这不是检查分配是否成功的好方法，因为如果未定义NDEBUG，它将在失败时中止应用程序，并且

将忽略失败！

-

Richard Heathfield

Usenet是一个奇怪的地方 - dmr 29/7/1999
http://www.cpax.org.uk

电子邮件：rjh在上述域名， - www。

In C90, assert requires an integer expression:

assert(pArr != NULL);

but this is not a good way to check whether the allocation succeeded, as
it will abort the application on failure if NDEBUG is not defined, and
will ignore the failure otherwise!
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.

3月27日晚上8:54，Richard Heathfield< ; r ... @ see.sig.invalidwrote：

On Mar 27, 8:54 pm, Richard Heathfield <[e-mail]:

hyperboogie说：

hyperboogie said:

Hello all

Hello all

我是C的新手，所以请提前接受我的道歉:-)

I''m pretty new to C, so please accept my apologies in advance :-)

我正在尝试为一个指向字符串的指针数组分配空间

（可以接受为椭圆形）在while循环中，并且在
之后
分配，当我断言时分配，断言失败！

I''m trying to allocate space for an array of pointers to strings
(which are accepted as ellipses) inside a while loop, and after the
allocation, when i "assert" the allocation, the assertion fails!!!

void printStrings（s1，...）{//省略号函数

...

...

void * myList;

int count = 1;

char * pArr = s1;

va_start（myList，s1）;

while（myList）{

pArr =（char *）realloc（pArr，++ count * sizeoff（char *） ）;

void printStrings(s1, ...){ //ellipses function
...
...
void *myList;
int count=1;
char *pArr=s1;
va_start(myList, s1);
while( myList ){
pArr = (char *) realloc(pArr, ++count * sizeoff(char*));

确保你的源文件顶部有＃include< stdlib.hnear，

输掉演员，使用temp，并获得正确的大小：


char * tmp = realloc（pArr，++ count * sizeof * pArr）;

if（tmp！= NULL）

{

pArr = tmp;

Make sure you have #include <stdlib.hnear the top of your source file,
lose the cast, use a temp, and get sizeof right:

char *tmp = realloc(pArr, ++count * sizeof *pArr);
if(tmp != NULL)
{
pArr = tmp;

assert（pArr）;

assert(pArr);

在C90中，断言需要一个整数表达式：


断言（pArr！= NULL）;


但这不是检查分配是否成功的好方法，因为如果未定义NDEBUG，它将在失败时中止应用程序，并且
$ b否则$ b将忽略失败！


-

Richard Heathfield

Usenet是一个奇怪的地方 - dmr 29/7 / 1999http：//www.cpax.org.uk

电子邮件：rjh在上述域名， - www。

In C90, assert requires an integer expression:

assert(pArr != NULL);

but this is not a good way to check whether the allocation succeeded, as
it will abort the application on failure if NDEBUG is not defined, and
will ignore the failure otherwise!

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999http://www.cpax.org.uk
email: rjh at the above domain, - www.

对不起 - 它不起作用.....

无论如何....为什么我会输掉演员表？ realloc返回void

*和pArr是char *，所以需要演员......或者我错了吗？

Sorry - it doesn''t work ....
in any case .... why should I lose the cast? realloc returns void
* and pArr is char * , so a cast is required ... or am I wrong?

在3月27日，19：38，hyperboogie， < hyperboo ... @ gmail.comwrote：

On 27 Mar, 19:38, "hyperboogie" <[e-mail]:

Hello all


我是C的新手，所以请提前接受我的道歉:-)


我正在尝试为字符串指针数组分配空间

（被接受为椭圆形）在一个while循环内，并且在

分配之后，当我断言时分配，断言失败!!!


void printStrings（s1，...）{//省略函数

...

...

void * myList;

int count = 1;

char * pArr = s1;

va_start（myList，s1）;

while（myList）{

pArr =（char *）realloc（pArr，++ count * sizeoff（char *） ））;

Hello all

I''m pretty new to C, so please accept my apologies in advance :-)

I''m trying to allocate space for an array of pointers to strings
(which are accepted as ellipses) inside a while loop, and after the
allocation, when i "assert" the allocation, the assertion fails!!!

void printStrings(s1, ...){ //ellipses function
...
...
void *myList;
int count=1;
char *pArr=s1;
va_start(myList, s1);
while( myList ){
pArr = (char *) realloc(pArr, ++count * sizeoff(char*));

我的猜测：


您正在尝试重新分配pArr指向的内存。

第一次循环，pArr == s1。


如果您打电话的话如下：


printStrings（"这是s1指向的字符串，

等等），...


.. ..然后我觉得很有可能字符串这是

字符串将被s1指向将有静态存储/是

由于字符串池/等等只读*所以我不认为

realloc''这个记忆是有效的。


* I 毫无疑问，这个术语是错误的，但是给它十分钟就可以了。

你很快就会看到一百个人纠正我了！


希望帮助，

道格

My guess:

You are attempting to realloc the memory pointed to by pArr. The
first time through the loop, pArr == s1.

If you are calling with something like:

printStrings("This is the string which will be pointed to by s1",
etc., etc., ...

....then I think there''s a good chance that the string "This is the
string which will be pointed to by s1" will have static storage/be
read-only due to string pooling/etc.* So I don''t think that
realloc''ing this memory is valid.

* I''ve no doubt got the terminology wrong, but give it ten minutes and
you''ll soon see a hundred people correct me!

Hope that helps,
Doug

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