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
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;
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
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.
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;
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?
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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