unordered_map 在 rcpp 中的使用 [英] unordered_map use in rcpp
问题描述
我是一个尝试在 Rcpp 中使用标准模板库 (STL) 学习数据结构和算法实现的新手.
I am a newbie trying to learn data structure and algorithm implementation using Standard Template Library (STL) in Rcpp.
我正在尝试使用 Rcpp 中的 unordered_map 实现一个非常基本的哈希表,从 Hadley 的 高级 R
I am trying to implement a very basic hash table using unordered_map in Rcpp, taking a hint from Hadley's Advanced R
这是我想在 Rcpp 中实现的 C++ 代码(取自 element14 博客)
Here is the C++ code I want to implement in Rcpp (taken from element14 blog)
#include <unordered_map>
#include <string>
#include <iostream>
using namespace std;
int main()
{
unordered_map<string, string> hashtable;
hashtable.emplace("www.element14.com", "184.51.49.225");
cout << "IP Address: " << hashtable["www.element14.com"] << endl;
return 0;
}
我的相同代码的 Rcpp 版本是(请忽略 int main,我现在将其命名为 int hash)
My Rcpp version for the same code is (please ignore the int main, I will name it int hash for now)
// [[Rcpp::plugins(cpp11)]]
#include <Rcpp.h>
#include <unordered_map>
#include <string>
using namespace Rcpp;
//[[Rcpp::export]]
int hash_test{
std::unordered_map<std::string, std::string> hashtable;
hashtable.emplace("www.element14.com", "184.51.49.225");
Rcout << "IP Address: " << hashtable["www.element14.com"] << endl;
return 0;
}
运行中
sourceCpp("./hash_test.cpp")
sourceCpp("./hash_test.cpp")
我收到以下错误(我不是 C++ 专业人士,所以请忽略任何愚蠢的错误)
I get the following errors (I am not a C++ professional, so please ignore any silly mistakes)
hash_test.cpp:11:46: error: expected primary-expression before ‘hashtable’
std::unordered_map<std::string, std::string> hashtable;
^
hash_test.cpp:11:46: error: expected ‘}’ before ‘hashtable’
hash_test.cpp:11:46: error: expected ‘,’ or ‘;’ before ‘hashtable’
hash_test.cpp:12:1: error: ‘hashtable’ does not name a type
hashtable.emplace("www.element14.com", "184.51.49.225");
^
hash_test.cpp:14:1: error: ‘Rcout’ does not name a type
Rcout << "IP Address: " << hashtable["www.element14.com"] << endl;
^
hash_test.cpp:15:1: error: expected unqualified-id before ‘return’
return 0;
^
hash_test.cpp:16:1: error: expected declaration before ‘}’ token
}
^
make: *** [hash_test.o] Error 1
Error in sourceCpp("./CDM_Open_Source_ME/kohls_model/hash_test.cpp") :
Error 1 occurred building shared library.
In addition: Warning message:
No function found for Rcpp::export attribute at hash_test.cpp:9
坦率地说,我不知道如何调试代码.请帮忙.
I frankly dont know how to debug the code. Please help.
推荐答案
这实际上只是缺少 hash_test
旁边的 ()
.
This was really just missing ()
next to hash_test
.
以下工作:
// [[Rcpp::plugins(cpp11)]]
#include <Rcpp.h>
#include <unordered_map>
#include <string>
// [[Rcpp::export]]
int hash_test() { // missed the ()
std::unordered_map<std::string, std::string> hashtable;
hashtable.emplace("www.element14.com",
"184.51.49.225");
Rcpp::Rcout << "IP Address: " << hashtable["www.element14.com"] << std::endl;
return 0;
}
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