Sub sequential C calls to R doesn't work - c++

Question

I'm writing a c++ function that takes in a R-call and evaluates it. The function returns as expected whenever I compile with a single call to it.
But when there are sub sequential calls to my function it gets stuck when I run the object file.
How would I re-instantiate the R instance after a single function call?
The method below gets stuck when there are two calls to my function but works fine when I do one call.
int main(int argc, char* argv[]){
double result1 = calculateScalar(input2);
std::cout << "Result 1 " << result1;
double result2 = calculateScalar(input2);
std::cout << "Result 2 " <<result2;
return 0;
}
double calculateScalar(const char* RCALL){
SEXP formula, result;
ParseStatus status;
R_xlen_t len;
int errorStatus;
try {
Rf_initEmbeddedR(0, NULL);
Rf_protect(formula = mkString(RCALL));
Rf_protect(formula = R_ParseVector(formula, 1, &status, R_NilValue));
result = R_tryEval(VECTOR_ELT(formula,0), R_GlobalEnv, &errorStatus);
PROTECT(result);
len = xlength(result);
UNPROTECT(3);
Rf_endEmbeddedR(0);
return (double) getNumericScalar(result);
} catch(std::exception& e){
std::cout << "Standard exception: " << e.what();
}
//Clean up R
Rf_endEmbeddedR(0);
exit(0);
}

Answer 1

Instead of reinventing the wheel, you could just RInside:
edd#brad:~/git/rinside/inst/examples/standard(master)$ make rinside_sample3
ccache g++ -I/usr/share/R/include -I/usr/local/lib/R/site-library/Rcpp/include \
-I/usr/local/lib/R/site-library/RInside/include -g -O3 -Wall -pipe -Wno-unused \
-pedantic -Wall rinside_sample3.cpp -Wl,--export-dynamic -fopenmp\
-L/usr/lib/R/lib -lR -lpcre -llzma -lbz2 -lz -lrt -ldl -lm \
-lblas -llapack -L/usr/local/lib/R/site-library/RInside/lib -lRInside \
-Wl,-rpath,/usr/local/lib/R/site-library/RInside/lib -o rinside_sample3
edd#brad:~/git/rinside/inst/examples/standard(master)$
builds it (automagically using an automated `GNUmakefile) from this simple source file.
Running it yields:
edd#brad:~/git/rinside/inst/examples/standard(master)$ ./rinside_sample3
Call:
lm(formula = Fertility ~ ., data = swiss)
Residuals:
Min 1Q Median 3Q Max
-15.2743 -5.2617 0.5032 4.1198 15.3213
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 66.91518 10.70604 6.250 1.91e-07 ***
Agriculture -0.17211 0.07030 -2.448 0.01873 *
Examination -0.25801 0.25388 -1.016 0.31546
Education -0.87094 0.18303 -4.758 2.43e-05 ***
Catholic 0.10412 0.03526 2.953 0.00519 **
Infant.Mortality 1.07705 0.38172 2.822 0.00734 **
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 7.165 on 41 degrees of freedom
Multiple R-squared: 0.7067, Adjusted R-squared: 0.671
F-statistic: 19.76 on 5 and 41 DF, p-value: 5.594e-10
And now from C++
Estimate Std. Error t value Pr(>|t|)
(Intercept) 66.9152 10.706 6.25023 1.90605e-07
Agriculture -0.172114 0.0703039 -2.44814 0.0187272
Examination -0.258008 0.253878 -1.01627 0.315462
Education -0.87094 0.183029 -4.75849 2.4306e-05
Catholic 0.104115 0.0352579 2.95297 0.00519008
Infant.Mortality 1.07705 0.38172 2.82157 0.00733572
edd#brad:~/git/rinside/inst/examples/standard(master)$
A few things to note:
I picked this example (among literally dozens of other in the package) as it contains multiple eval...() calls in the C++ code.
It is also cute as it redoes lm() for you.
The actual compilation following make rinside_sample3 will vary from system to system; on mine it reflect some parameters I set in ~/.R/Makevars
I manually narrow the display by four spaces to make it fit.