问题

这里是代码部分的翻译：

我有一些C++代码，其中我必须确保在退出之前调用特定的析构函数，我想知道在调用[[noreturn]]函数之前是否已经调用了它。

所以我写了这个简单的示例
```cpp
#include <cstdio>
#include <cstdlib>
class A {
        char *i;
public:
        A() : i{new char[4]} {}
        ~A() { delete[] i; }
        void hello() { puts(i); }
};

int func()
{
        A b;
        exit(1);
        b.hello(); // Not reached
}

我使用g++ /tmp/l.cc -S -O0编译后，得到了以下汇编代码

	.file	"l.cc"
	.text
	.section	.text._ZN1AC2Ev,"axG",@progbits,_ZN1AC5Ev,comdat
	.align 2
	.weak	_ZN1AC2Ev
	.type	_ZN1AC2Ev, @function
_ZN1AC2Ev:
.LFB18:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$16, %rsp
	movq	%rdi, -8(%rbp)
	movl	$4, %edi
	call	_Znam
	movq	%rax, %rdx
	movq	-8(%rbp), %rax
	movq	%rdx, (%rax)
	nop
	leave
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE18:
	.size	_ZN1AC2Ev, .-_ZN1AC2Ev
	.weak	_ZN1AC1Ev
	.set	_ZN1AC1Ev,_ZN1AC2Ev
	.text
	.globl	func
	.type	func, @function
func:
.LFB24:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$16, %rsp
	leaq	-8(%rbp), %rax
	movq	%rax, %rdi
	call	_ZN1AC1Ev
	movl	$1, %edi
	call	exit
	.cfi_endproc
.LFE24:
	.size	func, .-func
	.ident	"GCC: (GNU) 12.2.1 20221121 (Red Hat 12.2.1-4)"
	.section	.note.GNU-stack,"",@progbits

显然没有调用析构函数。

在这种愚蠢的情况下，这不太重要，但如果我需要在退出之前关闭一个文件呢？

<details>
<summary>英文:</summary>

I have some C++ code in which I must be sure that a specific destructor is called before exiting and I was wondering whether or not it was called before a [[noreturn]] function.

So I wrote this simple dummy example
```cpp
#include &lt;cstdio&gt;
#include &lt;cstdlib&gt;
class A {
        char *i;
public:
        A() : i{new char[4]} {}
        ~A() { delete[] i; }
        void hello() { puts(i); }
};

int func()
{
        A b;
        exit(1);
        b.hello(); // Not reached
}

I compiled with g++ /tmp/l.cc -S -O0 and I got this assembly

	.file	"l.cc"
	.text
	.section	.text._ZN1AC2Ev,"axG",@progbits,_ZN1AC5Ev,comdat
	.align 2
	.weak	_ZN1AC2Ev
	.type	_ZN1AC2Ev, @function
_ZN1AC2Ev:
.LFB18:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$16, %rsp
	movq	%rdi, -8(%rbp)
	movl	$4, %edi
	call	_Znam
	movq	%rax, %rdx
	movq	-8(%rbp), %rax
	movq	%rdx, (%rax)
	nop
	leave
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE18:
	.size	_ZN1AC2Ev, .-_ZN1AC2Ev
	.weak	_ZN1AC1Ev
	.set	_ZN1AC1Ev,_ZN1AC2Ev
	.text
	.globl	func
	.type	func, @function
func:
.LFB24:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$16, %rsp
	leaq	-8(%rbp), %rax
	movq	%rax, %rdi
	call	_ZN1AC1Ev
	movl	$1, %edi
	call	exit
	.cfi_endproc
.LFE24:
	.size	func, .-func
	.ident	"GCC: (GNU) 12.2.1 20221121 (Red Hat 12.2.1-4)"
	.section	.note.GNU-stack,"",@progbits

There was clearly no call to the destructor.

In this stupid case it doesn't matter much, but what if I had to close a file before exiting?

答案1

得分: 3

除了使用 exit() 终止程序通常被认为是不良实践之外，你可以尝试以下方法：

int func()
{
    {
        A b;
        /* ... */
    } // 离开作用域 => 销毁 b
    exit(1);
}

PS：假设你不是在编写驱动程序，大多数内核（包括 Microsoft Windows NT、Unix（如 BSD）、XNU（macOS）和 Linux）在程序退出时会自动释放分配的内存。

int func()
{
    {
        A b;
        /* ... */
    } // Leaving scope => destructing b
    exit(1);
}