c++赋值问题

hhts1987 · #1

原程序：

代码：全选

hala@hala-desktop:~/test$ gdb 1
GNU gdb 6.6-debian
Copyright (C) 2006 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) list
1       #include<iostream.h>
2       int main()
3       {
4         int a(8);
5         int &ra=a;
6         cout<<(ra==a)<<endl;
7         cout<<(&ra==&a)<<endl;
8         cout<<(sizeof(ra)==sizeof(a))<<endl;
9         if(ra==a)cout<<"1";
10          else cout<<"0";
(gdb) break 2
Breakpoint 1 at 0x8048706: file 1.cpp, line 2.
(gdb) run
Starting program: /home/hala/test/1

Breakpoint 1, main () at 1.cpp:2
2       int main()
(gdb) step
main () at 1.cpp:4
4         int a(8);
(gdb) print a
$1 = 134514729
(gdb) step
5         int &ra=a;
(gdb) print ra
$2 = (int &) @0xb7fe0800: 1474660693
(gdb) print &a
$3 = (int *) 0xbffc2ecc
(gdb) print &ra
$4 = (int *) 0xb7fe0800
(gdb) step
6         cout<<(ra==a)<<endl;
(gdb) print a
$5 = 8
(gdb) print ra
$6 = (int &) @0xbffc2ecc: 8
(gdb) print &a
$7 = (int *) 0xbffc2ecc
(gdb) print &ra
$8 = (int *) 0xbffc2ecc
(gdb)

我想我有个疑惑：

代码：全选

main () at 1.cpp:4
4         int a(8);
(gdb) print a
$1 = 134514729
(gdb) step
5         int &ra=a;
(gdb) print ra
$2 = (int &) @0xb7fe0800: 1474660693
(gdb) print &a
$3 = (int *) 0xbffc2ecc
(gdb) print &ra
$4 = (int *) 0xb7fe0800

为什么这里的值不一样
而到后面这里

代码：全选

(gdb) step
6         cout<<(ra==a)<<endl;
(gdb) print a
$5 = 8
(gdb) print ra
$6 = (int &) @0xbffc2ecc: 8
(gdb) print &a
$7 = (int *) 0xbffc2ecc
(gdb) print &ra
$8 = (int *) 0xbffc2ecc
(gdb)

却一样了

dbzhang800 · #2

1.贴代码请用代码环境

2.你print a的时候a的初始化还没有执行。必须step一次再print a！

代码：全选

(gdb) step
main () at 1.cpp:4
4         int a(8);
(gdb) print a
$1 = 134514729