已解决，将PST定义的build、upd里面所有xx变量改成局部变量
by YoungL @ 2024-01-16 13:44:18
完整代码：
```cpp
#include <bits/stdc++.h>
#define mid ((l + r) >> 1)
#define ls t[x].l
#define rs t[x].r
#define val t[x].v
using namespace std;
int n, m, a[1000005];
struct PST
{
struct node
{
int l, r, v;
} t[20000005];
int rt[20000005], sz = 0, tp = 0;
inline int build(int l, int r)
{
int xx; // 不能用全局变量，否则递归后会被更改
xx = ++sz;
if (l == r)
{
t[xx].v = a[l];
return xx;
}
t[xx].l = build(l, mid);
t[xx].r = build(mid + 1, r);
return xx;
}
inline int qry(int x, int l, int r, int g)
{
if (l == r)
return val;
if (g <= mid)
return qry(ls, l, mid, g);
else
return qry(rs, mid + 1, r, g);
}
inline int upd(int x, int l, int r, int g, int v)
{
int xx;
if (l == r)
{
t[++sz].v = v;
return sz;
}
if (g <= mid)
{
xx = upd(ls, l, mid, g, v);
t[++sz].l = xx;
t[sz].r = rs;
return sz;
}
else
{
xx = upd(rs, mid + 1, r, g, v);
t[++sz].l = ls;
t[sz].r = xx;
return sz;
}
}
} tree;
int main()
{
scanf("%d %d", &n, &m);
for (int i = 1; i <= n; i++)
scanf("%d", &a[i]);
tree.rt[0] = tree.build(1, n);
int v, op, loc, value;
while (m--)
{
scanf("%d %d %d", &v, &op, &loc);
if (op == 1)
{
scanf("%d", &value);
tree.rt[++tree.tp] = tree.upd(tree.rt[v], 1, n, loc, value);
}
else
{
tree.rt[++tree.tp] = tree.rt[v];
printf("%d\n", tree.qry(tree.rt[v], 1, n, loc));
}
}
return 0;
}
```
by YoungL @ 2024-01-16 13:45:23
@[YoungL](/user/1050683) 已解决，谢谢
by Br00k5xx @ 2024-01-18 14:58:02