Rcpp Error Null value passed as symbol address - r

Question

I am new to Rcpp.
I created an rcpp function which takes a dataframe with 2 columns and a vector as input, and returns a vector.
My data are as below
set.seed(10)
min= sort(rnorm(1000,800,sd=0.1))
max= min+0.02
k=data.frame(min,max)
explist= sort(rnorm(100,800,sd=0.2))
Then I call the cfilter.cpp
k$output <- cfilter(k,explist)
#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
CharacterVector cfilter(DataFrame k, NumericVector explist) {
NumericVector col1 = k["min"];
NumericVector col2 = k["max"];
NumericVector exp = explist ;
int n = col1.size();
int j = 0;
CharacterVector out(n);
for (int i=0; i<n ; i++){
out[i]=NA_STRING;
while(exp[j]<= col2[i]){
if( exp[j]>= col1[i] && exp[j]<= col2[i] ){
out[i]="Y";
break;
}
else if(exp[j]>col2[i]){
break;
}
else {
j++ ;
}
}
}
return out;
}
It run perfectly fine for 16171 times I called it. And then suddenly, in the loop 16172 it just stops with an error:
> myfile$output<- cfilter(k,explist2)
Error in .Call(<pointer: (nil)>, k, explist) :
NULL value passed as symbol address
I checked k and explist for NA values but there aren't any, there is no problem whatsoever with the input.
I have no clue how to fix this and what causes this error.
Thanks in advance for any response

Answer 1

I came across the same problem. I'm not an Rcpp expert, nor C++ nor, a backend coding expert.
I have circumvented this problem by re-sourcing my cpp file every time I want to make a call of the function. So, for example if following is your for loop:
for(i in 1:SampleSize){
out[[I]]<-cfilter(k,explist)
}
Do something like:
for(i in 1:SampleSize){
sourceCpp("cfilter.cpp")
out[[i]]<-cfilter(k,explist)
}
Again, I don't know exactly why this worked for me, but it worked. Based on my shallow knowledge of C++, it might be related to memory allocation and that every time you source, memory is released and hence there is no mis-allocation. But I think this is a very wild guess.
Best