C 语言中的constructor与destructor属性

ゞ浴缸里的玫瑰 2022-12-01 05:21 173阅读 0赞

GCC可以给函数若干属性，其中constructor就是其中一个。具体有哪些属性，可以看GCC的文档。

[公共属性：https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html\#Common-Function-Attributes][https_gcc.gnu.org_onlinedocs_gcc_Common-Function-Attributes.html_Common-Function-Attributes]

[所有属性：http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html][http_gcc.gnu.org_onlinedocs_gcc_Function-Attributes.html]

在上面文档中有对于constructor与destructor的描述：

引用

> `constructor`
> 
> `destructor`
> 
> `constructor (priority)`
> 
> `destructor (priority)`
> 
>  
> 
> The `constructor` attribute causes the function to be called automatically before execution enters `main ()`. Similarly, the `destructor` attribute causes the function to be called automatically after `main ()` completes or `exit ()` is called. Functions with these attributes are useful for initializing data that is used implicitly during the execution of the program.
> 
> On some targets the attributes also accept an integer argument to specify a priority to control the order in which constructor and destructor functions are run. A constructor with a smaller priority number runs before a constructor with a larger priority number; the opposite relationship holds for destructors. So, if you have a constructor that allocates a resource and a destructor that deallocates the same resource, both functions typically have the same priority. The priorities for constructor and destructor functions are the same as those specified for namespace-scope C++ objects (see [C++ Attributes][C_ Attributes]). However, at present, the order in which constructors for C++ objects with static storage duration and functions decorated with attribute `constructor` are invoked is unspecified. In mixed declarations, attribute `init_priority` can be used to impose a specific ordering.
> 
> Using the argument forms of the `constructor` and `destructor` attributes on targets where the feature is not supported is rejected with an error.

大致意思就是，可以给一个函数赋予constructor或destructor，其中constructor在main开始运行之前被调用，destructor在main函数结束后被调用。如果有多个constructor或destructor，可以给每个constructor或destructor赋予优先级，对于constructor，优先级数值越小，运行越早（优先级 0 到 100 为实现所保留，所以最小为101）。destructor则相反，优先级数值越小，运行越晚（优先级 0 到 100 为实现所保留，所以最小为101）。  
下面是一个例子：

C代码 ![收藏代码][format_png]

#include <stdio.h>
     
    void begin(void) __attribute__((destructor(103)));
    void end(void) __attribute__((destructor(102)));
     
    int main(void)
    {
            printf ("\nInside main()\n");
    
            return 0;
    }
    
    void begin(void)
    {
            printf ("\nIn begin()\n");
    }
    
    void end(void)
    {
            printf ("\nIn end()\n");
    }

运行的结果为：

Inside main()

In begin()

In end()

reference：[https://blog.csdn.net/xiaofei125145/article/details/52597256][https_blog.csdn.net_xiaofei125145_article_details_52597256]

[https_gcc.gnu.org_onlinedocs_gcc_Common-Function-Attributes.html_Common-Function-Attributes]: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
[http_gcc.gnu.org_onlinedocs_gcc_Function-Attributes.html]: http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
[C_ Attributes]: https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Attributes.html#C_002b_002b-Attributes
[format_png]: /images/20221123/c8ba7857e6614fefb59126939d948cff.png
[https_blog.csdn.net_xiaofei125145_article_details_52597256]: https://blog.csdn.net/xiaofei125145/article/details/52597256