[使用gdb用Rcpp调试R软件包的C ++代码无法使用R_PV（未知返回类型）打印变量值

Question

我已经在Ubuntu 18.04上使用RStudio来创建一个使用Rcpp的hello world R包，如Rcpp Package Development中所述：

我的~/.R/Makevars仅包含行

CXXFLAGS=-g -O0 -Wall

并且在pkg构建期间，我可以看到应用了这些标志。

在遇到断点后，如何打印R向量的当前值（CharacterVector中的C ++类NumericVector或gdb？

[(gdb) p R_PV(x)（如Writing R Extensions中所述）显示错误（可能是因为SEXP被包装了？）：

(gdb) whatis x
type = Rcpp::CharacterVector

我的调试会话：

R -d gdb --vanilla
(gdb) run
library(RcppTestPkg)
# type Strg + X to break into gdb to set a breakpoint
(gdb) break rcpp_hello_world.cpp:8
(gdb) cont
rcpp_hello_world()
Breakpoint 1, rcpp_hello_world () at rcpp_hello_world.cpp:8
8       NumericVector y   = NumericVector::create( 0.0, 1.0 ) ;
(gdb) n
9       List z            = List::create( x, y ) ;
(gdb) n
11      return z ;
(gdb) info locals
x = {<Rcpp::PreserveStorage<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {
    data = 0x5555562c4360}, <Rcpp::SlotProxyPolicy<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::AttributeProxyPolicy<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::NamesProxyPolicy<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::RObjectMethods<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::VectorBase<16, true, Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<Rcpp::traits::expands_to_logical__impl<16>> = {<No data fields>}, <No data fields>}, cache = {
    p = 0x7fffffffba10}}
y = {<Rcpp::PreserveStorage<Rcpp::Vector<14, Rcpp::PreserveStorage> >> = {
    data = 0x5555562c43d0}, <Rcpp::SlotProxyPolicy<Rcpp::Vector<14, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::AttributeProxyPolicy<Rcpp::Vector<14, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::NamesProxyPolicy<Rcpp::Vector<14, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::RObjectMethods<Rcpp::Vector<14, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::VectorBase<14, true, Rcpp::Vector<14, Rcpp::PreserveStorage> >> = {<Rcpp::traits::expands_to_logical__impl<14>> = {<No data fields>}, <No data fields>}, cache = {
    start = 0x5555562c43f8}}
z = {<Rcpp::PreserveStorage<Rcpp::Vector<19, Rcpp::PreserveStorage> >> = {
    data = 0x5555562c4440}, <Rcpp::SlotProxyPolicy<Rcpp::Vector<19, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::AttributeProxyPolicy<Rcpp::Vector<19, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::NamesProxyPolicy<Rcpp::Vector<19, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::RObjectMethods<Rcpp::Vector<19, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::VectorBase<19, true, Rcpp::Vector<19, Rcpp::PreserveStorage> >> = {<Rcpp::traits::expands_to_logical__impl<19>> = {<No data fields>}, <No data fields>}, cache = {
    p = 0x7fffffffbab0}}
(gdb) p x
$3 = {<Rcpp::PreserveStorage<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {
    data = 0x5555562c4360}, <Rcpp::SlotProxyPolicy<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::AttributeProxyPolicy<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::NamesProxyPolicy<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::RObjectMethods<Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<No data fields>}, <Rcpp::VectorBase<16, true, Rcpp::Vector<16, Rcpp::PreserveStorage> >> = {<Rcpp::traits::expands_to_logical__impl<16>> = {<No data fields>}, <No data fields>}, cache = {
    p = 0x7fffffffba10}}

(gdb) p R_PV(x)
'R_PV' has unknown return type; cast the call to its declared return type

Edit：这是该函数的源代码：

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
List rcpp_hello_world() {

    CharacterVector x = CharacterVector::create( "foo", "bar" )  ;
    NumericVector y   = NumericVector::create( 0.0, 1.0 ) ;
    List z            = List::create( x, y ) ;

    return z ;
}

Answer 1

(gdb) p R_PV(x)