使用gdb使用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 [英] Debugging C++ code of an R package with Rcpp using gdb cannot print variable value with R_PV (unknown return type)
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问题描述
我已经在Ubuntu 18.04上使用RStudio通过Rcpp创建了一个hello world R包，如
（gdb）whatis x
type = Rcpp :: CharacterVector
我的调试会话：
R -d gdb --vanilla
（gdb）运行
库（RcppTestPkg ）
＃键入Strg + X进入gdb以设置断点
（gdb）break rcpp_hello_world.cpp：8
（gdb）cont
rcpp_hello_world（）
断点1，rcpp_hello_world.cpp上的rcpp_hello_world（）：8
8 NumericVector y = NumericVector :: create（0.0，1.0）;
（gdb）n
9列表z =列表:: create（x，y）;
（gdb）n
11返回z;
（gdb）info locals
x = {< Rcpp :: PreserveStorage< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {{
data = 0x5555562c4360}，< Rcpp :: SlotProxyPolicy< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: AttributeProxyPolicy< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: NamesProxyPolicy< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: RObjectMethods< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: VectorBase< 16，是，Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {< Rcpp :: traits :: expands_to_logical__impl<> 16; = {<无数据字段>}，<无数据字段>}，缓存= {
p = 0x7fffffffba10}}
y = {< Rcpp :: PreserveStorage< Rcpp :: Vector< 14，Rcpp :: PreserveStorage> >> = {{
data = 0x5555562c43d0}，< Rcpp :: SlotProxyPolicy< Rcpp :: Vector< 14，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: AttributeProxyPolicy< Rcpp :: Vector< 14，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: NamesProxyPolicy< Rcpp :: Vector< 14，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: RObjectMethods< Rcpp :: Vector< 14，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: VectorBase< 14，是，Rcpp :: Vector< 14，Rcpp :: PreserveStorage> >> = {< Rcpp :: traits :: expands_to_logical__impl< 14> = {<无数据字段>}，<无数据字段>}，缓存= {
start = 0x5555562c43f8}}
z = {< Rcpp :: PreserveStorage< Rcpp :: Vector< 19， Rcpp :: PreserveStorage> >> = {{
data = 0x5555562c4440}，< Rcpp :: SlotProxyPolicy< Rcpp :: Vector< 19，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: AttributeProxyPolicy< Rcpp :: Vector< 19，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: NamesProxyPolicy< Rcpp :: Vector< 19，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: RObjectMethods< Rcpp :: Vector< 19，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: VectorBase< 19，是，Rcpp :: Vector< 19，Rcpp :: PreserveStorage> >> = {< Rcpp :: traits :: expands_to_logical__impl< 19> = {<无数据字段>}，<无数据字段>}，缓存= {
p = 0x7fffffffbab0}}
（gdb）px
$ 3 = {< Rcpp :: PreserveStorage< ; Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {{
data = 0x5555562c4360}，< Rcpp :: SlotProxyPolicy< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: AttributeProxyPolicy< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: NamesProxyPolicy< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: RObjectMethods< Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {<没有数据字段>}，< Rcpp :: VectorBase< 16，是，Rcpp :: Vector< 16，Rcpp :: PreserveStorage> >> = {< Rcpp :: traits :: expands_to_logical__impl<> 16; = {<无数据字段>}，<无数据字段>}，缓存= {
p = 0x7fffffffba10}}
（gdb）p R_PV（x）
' R_PV'的返回类型未知；将调用强制转换为其声明的返回类型
（gdb）p x-> data
$ 5 =（SEXP）0x5555566d2308
（gdb）p R_PV（x-> data ）
'R_PV'具有未知的返回类型；将调用转换为声明的返回类型
编辑：这是该函数的源代码：
#include< Rcpp.h>
使用命名空间Rcpp;
// [[Rcpp :: export]]
清单rcpp_hello_world（）{
CharacterVector x = CharacterVector :: create（ foo， bar ）;
NumericVector y = NumericVector :: create（0.0，1.0）;
List z = List :: create（x，y）;
返回z;
}
解决方案
（gdb）p R_PV（x）
在我的 R 源， R_PV 是返回 void 的函数。改为尝试以下操作：
（gdb）调用R_PV（x）
正如Dirk Eddelbuettel所述，您仍然需要将正确的类型传递给 R_PV ，所以也许正确的命令是：
（gdb）调用R_PV（Rcpp :: wrap（& x））
I have used RStudio on Ubuntu 18.04 to create an hello world R package using Rcpp like described here in Rcpp Package Development:
My ~/.R/Makevars contain only the line
CXXFLAGS=-g -O0 -Wall
and during pkg build I can see that these flags are applied.
How can print the current value of an R vector (C++ classes CharacterVector or NumericVector in gdb after hitting a breakpoint?
(gdb) p R_PV(x) (as explained in Writing R Extensions) shows an error (perhaps because the SEXP is wrapped?):
(gdb) whatis x
type = Rcpp::CharacterVector
My debug session:
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
(gdb) p x->data
$5 = (SEXP) 0x5555566d2308
(gdb) p R_PV(x->data)
'R_PV' has unknown return type; cast the call to its declared return type
Edit: Here`s the source code of the function:
#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 ;
}
解决方案
(gdb) p R_PV(x)
In my R source, R_PV is a function returning void. Try this instead:
(gdb) call R_PV(x)
As Dirk Eddelbuettel noted, you still need to pass the right type to R_PV, so perhaps the correct command is:
(gdb) call R_PV(Rcpp::wrap(&x))
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