C链接传递给C库函数指针 [英] C linkage for function pointer passed to C library

问题描述

我的情况是pretty简单：我想我的C ++程序来处理Unix的信号。要做到这一点，glibc的提供signal.h中的函数叫做的sigaction ，它预计将收到一个函数指针作为其第二个参数。

 的externC
{
无效uponSignal（INT）;
}无效uponSignal（INT）
{
    //设置一些标志来退出程序
}静态的
无效installSignalHandler（）
{
    //初始化信号处理程序
    静态结构的sigaction sighandler;
    memset的（安培; sighandler，0，sizeof的（结构的sigaction））;
    sighandler.sa_handler = uponSignal;    //安装
    的sigaction（SIGINT，和放大器; sighandler，nullptr）;
}
 

我的问题是：在的externC联动符必要

？

奖金问题：可以uponSignal声明静态

解决方案

  

我的问题是：在的externC联动符必要

？

有关最大的可移植性，是的; C ++标准只能通过声明的externC。功能保证了用C互操作性

实际上，没有;最明智的ABI（包括glibc的使用的GNU ABI）将使用C和C ++非成员相同的调用约定（和静态成员）功能，让的externC只需要共享语言之间的函数名。

  

奖金的问题：能 uponSignal 声明为static

？

是的。只需要外部链接从其他翻译单元名称来访问功能;这是没有必要通过一个函数指针调用的函数。

My case is pretty simple: I want my C++ program to deal with Unix signals. To do so, glibc provides a function in signal.h called sigaction, which expects to receive a function pointer as its second argument.

extern "C"
{
void uponSignal(int);
}

void uponSignal(int)
{
    // set some flag to quit the program
}

static
void installSignalHandler()
{
    // initialize the signal handler
    static struct sigaction sighandler;
    memset( &sighandler, 0, sizeof(struct sigaction) );
    sighandler.sa_handler = uponSignal;

    // install it
    sigaction( SIGINT, &sighandler, nullptr );
}

My question is: is the extern "C" linkage specifier necessary?

Bonus question: can uponSignal be declared static?

解决方案

My question is: is the extern "C" linkage specifier necessary?

For maximum portability, yes; the C++ standard only guarantees interoperability with C via functions declared extern "C".

Practically, no; most sensible ABIs (including the GNU ABI used by glibc) will use the same calling convention for C and C++ non-member (and static member) functions, so that extern "C" is only needed to share the function name between languages.

Bonus question: can uponSignal be declared static?

Yes. External linkage is only needed to access the function by name from other translation units; it's not necessary to call the function via a function pointer.

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