c++, object life-time of anonymous (unnamed) variables
- by Joe Steeve
In the following code, the object constructed in the last line of 'main()', seems to be destroyed before the end of the expression. The destructor is called before the '<<' is executed. Is this how it is supposed to be?
#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";
}
This is the output:
Hello
from A: 0x80495f7
from A: Hello
This is the gdb log:
(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)
