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问题描述
在C中创建单身人士的最佳方法是什么?并发解决方案会很好.
我知道C不是您将使用Singleton的母语.
推荐答案
首先，C不适合OO编程.如果您这样做，您将一路战斗.其次，单例只是带有一些封装的静态变量.因此，您可以使用静态全局变量.但是，全球变量通常存在太多与之相关的疾病.否则，您可以使用函数本地静态变量，例如:
int *SingletonInt() {
static int instance = 42;
return &instance;
}
或更智能的宏:
#define SINGLETON(t, inst, init) t* Singleton_##t() { \
static t inst = init; \
return &inst; \
}
#include <stdio.h>
/* actual definition */
SINGLETON(float, finst, 4.2);
int main() {
printf("%f\n", *(Singleton_float()));
return 0;
}
最后，请记住，单身人士大部分被滥用.很难使它们正确，尤其是在多线程环境下...
其他推荐答案
您不需要. C已经有全局变量，因此您不需要工作来模拟它们.
其他推荐答案
与C ++版本几乎相同.只需具有返回实例指针的函数即可.它可以是函数内部的静态变量.根据平台，用关键部分或Pthread Mutex包裹功能主体.
#include <stdlib.h>
struct A
{
int a;
int b;
};
struct A* getObject()
{
static struct A *instance = NULL;
// do lock here
if(instance == NULL)
{
instance = malloc(sizeof(*instance));
instance->a = 1;
instance->b = 2;
}
// do unlock
return instance;
};
请注意，您也需要一个函数来释放单例.特别是如果它抓住任何在流程退出时未自动发布的系统资源.
问题描述
What's the best way to create a singleton in C? A concurrent solution would be nice.
I am aware that C isn't the first language you would use for a singleton.
推荐答案
First, C is not suitable for OO programming. You'd be fighting all the way if you do. Secondly, singletons are just static variables with some encapsulation. So you can use a static global variable. However, global variables typically have far too many ills associated with them. You could otherwise use a function local static variable, like this:
int *SingletonInt() {
static int instance = 42;
return &instance;
}
or a smarter macro:
#define SINGLETON(t, inst, init) t* Singleton_##t() { \
static t inst = init; \
return &inst; \
}
#include <stdio.h>
/* actual definition */
SINGLETON(float, finst, 4.2);
int main() {
printf("%f\n", *(Singleton_float()));
return 0;
}
And finally, remember, that singletons are mostly abused. It is difficult to get them right, especially under multi-threaded environments...
其他推荐答案
You don't need to. C already has global variables, so you don't need a work-around to simulate them.
其他推荐答案
It's the same as the C++ version pretty much. Just have a function that returns an instance pointer. It can be a static variable inside the function. Wrap the function body with a critical section or pthread mutex, depending on platform.
#include <stdlib.h>
struct A
{
int a;
int b;
};
struct A* getObject()
{
static struct A *instance = NULL;
// do lock here
if(instance == NULL)
{
instance = malloc(sizeof(*instance));
instance->a = 1;
instance->b = 2;
}
// do unlock
return instance;
};
Note that you'd need a function to free up the singleton too. Especially if it grabs any system resources that aren't automatically released on process exit.
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