[英]How to cast one parameter in function as void pointer parameter to an integer
I am having this function fun, where I am passing the nums structure as a parameter. 我在使用此函数很有趣,在这里我将nums结构作为参数传递。 The thing is that I need to convert this field into an integer inside the function.
问题是我需要将此字段转换为函数内部的整数。 How can I do this without changing the way I am passing the structure in the function?
如何在不更改在函数中传递结构的方式下执行此操作?
Here is what i am trying to do: 这是我想做的事情:
struct node{
char *str;
struct node *next;
};
struct numbers{
struct node *head;
int *new_a;
};
void *fun(void *args);
int main(int argc , char *argv[])
{
int *new_a, num_a;
struct node *head=NULL;
struct numbers *args = (struct numbers *)malloc(sizeof(struct numbers));
num_a = returnNum();
pthread_t pthread;
new_a = malloc(1);
*new_a = num_a;
args->new_a=new_a;
if( pthread_create( &pthread , NULL , (void *) &fun , (void *) &args) < 0)
{
perror("could not create thread");
return 1;
}
}
void *fun(void *args){
//void *num_a = (int *) args->new_a;
//int num_a = *(int*)(args->new_a);
struct numbers *temp_str = (struct numbers *) (*args);
int num_a = (int) *(args->new_a);
...
}
Also, how can I do the casting for the head node? 另外,如何对头节点进行转换? Can anyone please advice?
任何人都可以请教吗?
Since a struct numbers *
is being passed to fun
, you need to assign the parameter to a variable of this type. 由于将
struct numbers *
传递给fun
,因此您需要将参数分配给这种类型的变量。 Then you can use the struct. 然后,您可以使用该结构。
void *fun(void *arg){
struct numbers *temp_str = arg; // no need to cast from void *
int num_a = temp_str->new_a;
...
}
There's also a problem with how you populate the struct: 如何填充结构也存在问题:
int *new_a, num_a;
...
new_a = malloc(1);
*new_a = num_a;
args->new_a=new_a;
You're not allocating enough space for new_a
. 您没有为
new_a
分配足够的空间。 You only allocate 1 byte, but an int
on most systems is 4 bytes. 您只分配1个字节,但是在大多数系统上,一个
int
是4个字节。 When you subsequently read and write from this memory location, you read/write past the end of the memory that was allocated. 当您随后从该内存位置进行读写时,您将在已分配内存的末尾进行读写。 This invokes undefined behavior which in this case manifests as a crash..
这将导致未定义的行为 ,在这种情况下将显示为崩溃。
You can fix this by allocating the proper amount of space: 您可以通过分配适当的空间来解决此问题:
new_a = malloc(sizeof(*new_a));
However, you don't need to use dynamic memory allocation for this field at all. 但是,您根本不需要为此字段使用动态内存分配。 Just declare
new_a
as int
and write to it directly: 只需将
new_a
声明为int
并直接写入即可:
struct numbers{
struct node *head;
int new_a;
};
...
args->new_a = returnNum();
You also don't need to take the address of args
. 您也不需要使用
args
的地址。 It's a pointer, so pass it to pthread_create
directly: 它是一个指针,因此将其直接传递给
pthread_create
:
if( pthread_create( &pthread , NULL , fun , args) < 0)
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.