GDB调试问题:在GDB调试步骤中看到的虚值

当我跳过第22行时，我仍然可以看到从y输出的奇怪值，这使我认为y没有正确初始化。但是当我再走2步到达返回行时，数字就正确了。

这里发生了什么?我试图关闭优化，但它不工作

 1#include <iostream>
 2#include <cstring>
 3#include <cmath>
 4using namespace std;
 5
 6const int MD = 10;
 7struct BigNumber{
 8  int digits[MD];
15  }
16
17  BigNumber(){
18    memset( digits, 0, sizeof(digits));
19  }
20
***21  BigNumber test(){
22    BigNumber p,c,y;// on this line , y is seen as garbage
23    p=c;// on this line , y is seen as garbage
24    c=y;
25    //y=p;                                                                                                                      
26    return y; // on this line, y returned to correct number
27=>}***
28
29
30  friend ostream& operator<<(ostream& out, const BigNumber& b );
31};
32
33ostream& operator<<(ostream& out, const BigNumber& b){
34  for( int i=MD-1; i>=0; i-- ){
35     out << b.digits[i];
36  }
37  return out;
38}
39
40
41
42int main( ){
43  BigNumber l("4");
44  BigNumber r;
45  BigNumber p,c,y;
46
47  r=l.test();
48  cout << r << endl;
49  cout << l.test() << endl;
50  return 0;
51}
28
(gdb) p p
$8 = {digits = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}}
(gdb) p c
$9 = {digits = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}}
(gdb) p y
$10 = {digits = {1171907, 1235664, -1208027616, 1, 1, 0, 1, 134513360, 134520860, 0}}
(gdb) n
(gdb) n
(gdb) p y
$11 = {digits = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}}