c++ - 检测到 'memory leak' 时，valgrind 中的实际指针是什么？

Question

如文档所述:

(5)  RRR -?-> BBB  (y)DR, (n)DL

Pointer chain legend:
- RRR: a root set node or DR block
- AAA, BBB: heap blocks
- --->: a start-pointer
- -?->: an interior-pointer

Leak Case legend:
- DR: Directly reachable
- IR: Indirectly reachable
- DL: Directly lost
- IL: Indirectly lost
- (y)XY: it's XY if the interior-pointer is a real pointer
- (n)XY: it's XY if the interior-pointer is not a real pointer
- (_)XY: it's XY in either case

Valgrind Documentation

案例一:

void *RRR;
int main()
{
    RRR = malloc(4);
    RRR = (char*)RRR + 2;
    return 0;
}

输出:

==3390== LEAK SUMMARY:
==3390==      possibly lost: 4 bytes in 1 blocks

案例2:

void *RRR;
int main()
{
    RRR = malloc(4);
    *(int*)RRR = 4;
    RRR = (char*)RRR + 2;
    return 0;
}

输出:

==3414== LEAK SUMMARY:
==3414==      possibly lost: 4 bytes in 1 blocks

两种情况输出相同的结果。 'real pointer'是什么意思？而'_'代表什么？

(y)XY:如果内部指针是一个真正的指针，它就是 XY。如何将XY变为真正的指针？

Answer 1

我知道这是一个有点老的问题，但也许对将来的人有帮助。

您的问题与以下文档陈述中的“真实指针”有关:

- (y)XY: it's XY if the interior-pointer is a real pointer
- (n)XY: it's XY if the interior-pointer is not a real pointer

此语句与内部指针相关。文档说内部指针可能是:

It might be a random junk value in memory, entirely unrelated, just a coincidence.

在这种情况下内部指针不被认为是真正的指针，所以在这种情况下

(5)  RRR -?-> BBB  (y)DR, (n)DL

将被视为直接失去内存((n)DL)。如果内部指针是一个指针变量，但是例如advanced 指向已分配内存块的中间，就像您在案例 2 中所做的那样，然后它被认为是直接可达的 ((y)DR)。

请注意，这是我对文档的理解，我是