先看一个例子:
1 #include <map> 2 3 int main() 4 { 5std::map<int,int> iMap; 6 7iMap[5] = 6; 8iMap[8] = 20; 9iMap[2] = 80; 10 11return 0; 12 }
看一下汇编:
(gdb) disassemble mainDump of assembler code for function main: 0x080486e4 <+0>:push %ebp 0x080486e5 <+1>:mov %esp,%ebp 0x080486e7 <+3>:and $0xfffffff0,%esp 0x080486ea <+6>:push %esi 0x080486eb <+7>:push %ebx 0x080486ec <+8>:sub $0x48,%esp 0x080486ef <+11>:lea 0x1c(%esp),%eax 0x080486f3 <+15>:mov %eax,(%esp) 0x080486f6 <+18>:call 0x80487b6 <_ZNSt3mapIiiSt4lessIiESaISt4pairIKiiEEEC2Ev> 0x080486fb <+23>:movl $0x5,0x34(%esp) 0x08048703 <+31>:lea 0x34(%esp),%eax 0x08048707 <+35>:mov %eax,0x4(%esp) 0x0804870b <+39>:lea 0x1c(%esp),%eax 0x0804870f <+43>:mov %eax,(%esp) 0x08048712 <+46>:call 0x8048830 <_ZNSt3mapIiiSt4lessIiESaISt4pairIKiiEEEixERS3_> 0x08048717 <+51>:movl $0x6,(%eax) 0x0804871d <+57>:movl $0x8,0x38(%esp) 0x08048725 <+65>:lea 0x38(%esp),%eax 0x08048729 <+69>:mov %eax,0x4(%esp) 0x0804872d <+73>:lea 0x1c(%esp),%eax 0x08048731 <+77>:mov %eax,(%esp) 0x08048734 <+80>:call 0x8048830 <_ZNSt3mapIiiSt4lessIiESaISt4pairIKiiEEEixERS3_> 0x08048739 <+85>:movl $0x14,(%eax) 0x0804873f <+91>:movl $0x2,0x3c(%esp) 0x08048747 <+99>:lea 0x3c(%esp),%eax 0x0804874b <+103>:mov %eax,0x4(%esp) 0x0804874f <+107>:lea 0x1c(%esp),%eax 0x08048753 <+111>:mov %eax,(%esp) 0x08048756 <+114>:call 0x8048830 <_ZNSt3mapIiiSt4lessIiESaISt4pairIKiiEEEixERS3_> 0x0804875b <+119>:movl $0x50,(%eax) 0x08048761 <+125>:mov $0x0,%ebx 0x08048766 <+130>:lea 0x1c(%esp),%eax 0x0804876a <+134>:mov %eax,(%esp) 0x0804876d <+137>:call 0x80487a2 <_ZNSt3mapIiiSt4lessIiESaISt4pairIKiiEEED2Ev> 0x08048772 <+142>:mov %ebx,%eax 0x08048774 <+144>:add $0x48,%esp 0x08048777 <+147>:pop %ebx 0x08048778 <+148>:pop %esi 0x08048779 <+149>:mov %ebp,%esp 0x0804877b <+151>:pop %ebp 0x0804877c <+152>:ret0x0804877d <+153>:mov %edx,%ebx 0x0804877f <+155>:mov %eax,%esi 0x08048781 <+157>:lea 0x1c(%esp),%eax 0x08048785 <+161>:mov %eax,(%esp) 0x08048788 <+164>:call 0x80487a2 <_ZNSt3mapIiiSt4lessIiESaISt4pairIKiiEEED2Ev> 0x0804878d <+169>:mov %esi,%eax 0x0804878f <+171>:mov %ebx,%edx 0x08048791 <+173>:mov %eax,(%esp) 0x08048794 <+176>:call 0x804861c <_Unwind_Resume@plt>End of assembler dump.
由0x080486f6可以看到,esp+0x1c是map的this指针.
在0x080486f6, 0x08048712,0x08048734, 0x08048756, 0x0804876d 打断点:
(gdb) b *0x080486f6Breakpoint 1 at 0x80486f6(gdb) b *0x08048712Breakpoint 2 at 0x8048712(gdb) b *0x08048734Breakpoint 3 at 0x8048734(gdb) b *0x08048756Breakpoint 4 at 0x8048756(gdb) b *0x0804876dBreakpoint 5 at 0x804876d
先看一下map在调用构造函数前后的变化:
(gdb) rStarting program: /home/xuzhina/code/s3/xuzhina_dump_c07_s3 Breakpoint 1, 0x080486f6 in main ()(gdb) x /8x $esp+0x1c0xbffff2bc:0x080485680x008702b80x0804b3c40xbffff2f80xbffff2cc:0x080496590x028ea5500x080484120x00000000(gdb) ni0x080486fb in main ()(gdb) x /8x $esp+0x1c0xbffff2bc:0x080485680x000000000x000000000xbffff2c00xbffff2cc:0xbffff2c00x000000000x080484120x00000000
参照bits/stl_map.h, bits/stl_tree.h里面的_Rb_tree_node_base, _Rb_tree_node, _Rb_tree, _Rb_tree_impl, map
的定义可知,头节点被初始化为
{_M_key_compare = 0x08048568,_M_color = 0x00000000,_M_parent = 0x00000000,_M_left = 0xbffff2c0,_M_right = 0xbffff2c0,_M_node_count = 0x00000000,}
再看一下,当map放入第一个元素时,会变成什么样.
(gdb) cContinuing.Breakpoint 2, 0x08048712 in main ()(gdb) ni0x08048717 in main ()(gdb) ni0x0804871d in main ()(gdb) x /8x $esp+0x1c0xbffff2bc:0x080485680x000000000x0804c0080x0804c0080xbffff2cc:0x0804c0080x000000010x000000050x00000000(gdb) x /8x 0x0804c0080x804c008:0x000000010xbffff2c00x000000000x000000000x804c018:0x000000050x000000060x000000000x00020fe1
可以看到头节点和第一个节点的值如下:
头节点
第一个节点
{
_M_key_compare = 0x08048568,
_M_color = 0x00000000,
_M_parent = 0x0804c008,
_M_left = 0x0804c008,
_M_right = 0x0804c008,
_M_node_count = 0x00000001,
}
{
_M_color = 0x00000001,
_M_parent = 0xbffff2c0,
_M_left = 0x00000000,
_M_right = 0x00000000,
_M_value_field.first = 0x00000005,
_M_value_field.second =0x00000006
}
伟人之所以伟大，是因为他与别人共处逆境时，
