rcpp代码错误？

Question

此代码在带有 Rcpp 的 R 上运行良好

 cppFunction('

 double getMean (NumericVector x) {

 int n = x.length() ;

 double mn = 0.0 ;

 for (int it = 0 ; it < n ; it++) {

 mn += x(it) / n ;

 }

 return(mn) ;

 }

 ')

但仅添加另一行会产生错误。这只是尝试Rcpp的简单代码，学习。我已将上面的大部分代码插入到一个循环中。

cppFunction('

double getMean (NumericVector x) {

for (int jt = 0 ; jt < 100000 ; jt++) {

int n = x.length() ;

double mn = 0.0 ;

for (int it = 0 ; it < n ; it++) {

mn += x(it) / n ;

} }

return(mn) ;

}

')

g++ -m64 -I"F:/Soft/R/R-31~1.1/include" -DNDEBUG     -I"F:/Soft/R/R-3.1.1/library/Rcpp/include"       -O2 -Wall  -mtune=core2 -c file65c22223500.cpp -o file65c22223500.o
file65c22223500.cpp: In function 'double getMean(Rcpp::NumericVector)':
file65c22223500.cpp:14:8: error: 'mn' was not declared in this scope
 return(mn) ;
        ^
file65c22223500.cpp:15:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
make: *** [file65c22223500.o] Error 1
 error message lost  executed command  'make -f "F:/Soft/R/R-31~1.1

/etc/x64/Makeconf" -f "F:/Soft/R/R-31~1.1/share/make/winshlib.mk" 

SHLIB_LDFLAGS='$(SHLIB_CXXLDFLAGS)' SHLIB_LD='$(SHLIB_CXXLD)' 

SHLIB="sourceCpp_30227.dll" WIN=64 TCLBIN=64 OBJECTS="file65c22223500.o"' has 2 status error in sourceCpp(code = code, env = env, rebuild = rebuild, showOutput = showOutput,  : 
  Error 1 occurred building shared library.

有什么问题？

Answer 1

您只需在 for loop 之外声明 mn。

当您在 for loop 中声明 mn 时，其范围仅限于 for 循环块。无法在该块之外访问它。如果您在循环外声明 mn，它将可以从整个功能块访问（就像在您提供的第一个代码中一样）。

rcpp代码错误？

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