Why does assert not work here?

Question

Here is the code:

#include <Rcpp.h>
#include <iostream>
#include <assert.h>
#include <stdio.h>

using namespace Rcpp;


// [[Rcpp::export]]
double eudist(NumericVector x, NumericVector y) {
    int nx = x.size();
    int ny = y.size();
    std::cout << nx << '\n' << ny << std::endl;
    assert(nx == ny);

    double dist=0;
    for(int i = 0; i < nx; i++) {
        dist += pow(x[i] - y[i], 2);
    }

    return sqrt(dist);
}

After sourcing it into R, I get the following result, apparently it does not abort when there is an error:

#////////////////////////////////////////////////////
sourceCpp('x.cpp')
#////////////////////////////////////////////////////
eudist(c(0, 0), c(1, 1))
2
2
[1] 1.4142
#////////////////////////////////////////////////////
eudist(c(0, 0), c(1, 1, 1))
2
3
[1] 1.4142

How are you compiling this? `assert` will be removed by the preprocessor if you define `NDEBUG`; that's probably what's happening. — Mike Seymour, Jan 28 '14 at 15:08
Oh, and to be a stickler: use `Rcpp::Rcout` instead of `std::cout` to write into R's i/o buffers. — Dirk Eddelbuettel, Jan 28 '14 at 17:02
Also, rather than edit your own question with the answer, you should create a new answer. — Scott Ritchie, Jan 29 '14 at 05:28

score 4 · Accepted Answer · answered Jan 28 '14 at 16:13

Note that assert() etc are explicitly prohibited for CRAN uploads. Quoting from the CRAN Repo Policy page:

The code and examples provided in a package should never do anything which might be regarded as malicious or anti-social. The following are illustrative examples from past experience.

Compiled code should never terminate the R process within which it is running. Thus C/C++ calls to assert/abort/exit, Fortran calls to STOP and so on must be avoided. Nor may R code call q().

So the answer about debug mode is technically correct, but also note that you are not supposed to use this if you plan to upload CRAN at some point.

score 3 · Answer 2 · answered Jan 29 '14 at 10:33

The problem is solved by using throw instead of assert, Rcpp will actually put things in a proper try-catch block, which is super nice.

#include <Rcpp.h>
#include <iostream>
#include <assert.h>
#include <stdio.h>

using namespace Rcpp;


// [[Rcpp::export]]
double eudist(NumericVector x, NumericVector y) {
    int nx = x.size();
    int ny = y.size();
    Rcout << nx << '\n' << ny << std::endl;

    if(nx != ny) {
        throw std::invalid_argument("Two vectors are not of the same length!");
    }

    double dist=0;
    for(int i = 0; i < nx; i++) {
        dist += pow(x[i] - y[i], 2);
    }

    return sqrt(dist);
}

score 0 · Answer 3 · answered Jan 28 '14 at 15:13

0

For g++ use -g to enable debug options:

g++ -g code.cpp

Or debug mode in Visual Studio.

answered Jan 28 '14 at 15:13

qstebom

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Why does assert not work here?

3 Answers3

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