求助，为什么strlen会直接RE

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
char s1[1000005],s2[1000005];
int len;
int sp[1000005];//max border
void Qiu_sp(){
    sp[1]=0;
    for(int i=2;i<=len;i++){
    	cout << "DEBUG::##IN##" << endl; 
        if(s2[sp[i-1]+1]==s2[i])sp[i]=sp[i-1]+1;
        else{
            int x=i-1;
            while(sp[x]!=0){
                if(s2[sp[x]+1]==s2[i]){
                    sp[i]=sp[x]+1;
                    break;
                }
                x=sp[x];
            }
            // sp[i]=sp[x]+1;
        }
    }
}
int main(){
//    cin >> s1+1;
//    cin >> s2+1;
    scanf("%s",s1+1);
    scanf("%s",s2+1);
//    cout << "666";
    len=strlen(s2)-1;
    Qiu_sp();
    // int tmp=1;
    for(int i=1,j=1;i<=strlen(s1)-1;i++,j++){
        if(s1[i]==s2[j]){
            if(j==len){
                cout << i-j+1 << endl;
                j=sp[j];
            }
        }
        else {
            j=sp[j];
        }
    }
    for(int i=1;i<=len;i++)cout << sp[i] << " ";
    return 0;
}