C++ c++；，匿名（未命名）变量的对象生存期

在下面的代码中，在“main（）”的最后一行中构造的对象似乎在表达式结束之前被销毁。在“之前调用析构函数我相信您看到的行为是因为“匿名临时变量不能作为非常量引用传递到函数中”的规则（当然不是真的，但在不同的编译器上有未定义的行为或不同的行为）。因此，它确实转到A，直到执行完full语句后才被删除

您遇到的问题不是由删除和打印非斜体数据引起的，而是由r值引用引起的。注释性实例只能通过值或常量引用传递

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这意味着你们的类将支持

操作符很好的解释，你们在我回答的时候发布了。
#include <string>
#include <sstream>
#include <iostream>

using std::string;
using std::ostringstream;
using std::cout;

class A : public ostringstream
{
public:
  A () {}
  virtual ~A ()
  {    
    string s;
    s = str();
    cout << "from A: " << s << std::endl;
  }
};

int
main ()
{
  string s = "Hello";
  A os;

  os << s;
  cout << os.str() << std::endl;

  A() << "checking this";
}

Hello
from A: 0x80495f7
from A: Hello

(gdb) b os.cxx : 18
Breakpoint 1 at 0x80492b1: file os.cxx, line 18. (2 locations)
(gdb) r
Starting program: /home/joe/sandbox/test/os 
Hello

Breakpoint 1, ~A (this=0xbffff37c, __in_chrg=<value optimized out>, __vtt_parm=<value optimized out>) at os.cxx:18
18     cout << "from A: " << s << std::endl;
(gdb) p s.c_str ()
$1 = 0x804b45c "0x80495f7"
(gdb) p *s.c_str ()
$2 = 48 '0'
(gdb) c
Continuing.
from A: 0x80495f7

Breakpoint 1, ~A (this=0xbffff2bc, __in_chrg=<value optimized out>, __vtt_parm=<value optimized out>) at os.cxx:18
18     cout << "from A: " << s << std::endl;
(gdb) p s.c_str ()
$3 = 0x804b244 "Hello"
(gdb) p *s.c_str ()
$4 = 72 'H'
(gdb) c
Continuing.
from A: Hello

Program exited normally.
(gdb)

struct A {
    f()
};

void g(A & a) {
}

void foo() {
    A a;
    a.f();
    g(a);

    A().f();
    g(A());  // This does not compile
}

class A
{
    ostringstream mystream;
public:
  A () {}
  virtual ~A ()
  {    
    cout << "from A: " << mystream.str(); << std::endl;
  }
  ostream & stream()
  {
       return mystream;
  }
};

int
main ()
{
  string s = "Hello";
  A os;

  os.stream() << s;    
  A().stream() << "checking this";
}

#define TRACE_ERROR if (A::testLevel(A::Error) A(A::Error).stream()
#define TRACE_INFO if (A::testLevel(A::Info) A(A::Info).stream()

void foo()
{
    int a = ..
    std::string s = ..
    TRACE_INFO << "Some information " << a << " message: " s;
}