c++ - Finding the index of a string inside a field of strings -

my apologies basic question, i'm new rcpp , c++ r.

i have field (arma::field) have initialized hold strings (arma::field<std::string> my_vector). have string std::string id somewhere inside field of strings, , find position of is. i'm used doing vectors , numbers similar below:

arma::vec fun(arma::vec input_vector){      // find vector equals 5 (for example)     uvec index = arma::find(input_vector == 5);      return index; } 

i tried exact same thing, given string instead of number compare:

arma::uvec fun(arma::vec input_vector, std::string id){      // find vector string id     uvec index = arma::find(input_vector == id);      return index; } 

this returns error

error: invalid operands binary expression ('arma::vec' (aka 'col<double>')      , 'std::string' (aka 'basic_string<char, char_traits<char>, allocator<char> >')) 

which made sense because vector not initialized contain strings. though don't think vector can initialized contain strings, because when tried arma::vec<std::string>, gives mess of errors.

this lead me fields can hold lot more kinds of variables.

arma::uvec fun(arma::field<std::string> input_field, std::string id){      // find vector equals 5 (for example)     uvec index = arma::find(input_field == id);      return index; } 

however returns

error: invalid operands binary expression ('arma::field<std::string>' ,       'std::string' (aka 'basic_string<char, char_traits<char>, allocator<char> >')) 

i have tried strcmp well, threw error

error: no viable conversion 'arma::field<std::string>' 'const char *' 

this leads me ask, how can find position of string within field?

i'm open changing types around works better, suspect using std::vector might work better or perhaps different kind haven't heard of. however, first experiments haven't been successful. if has hints on direction go, appreciated.

edit: clarified find arma::find instead of std::find not clear.

arma not support storage of std::string within data structures per matrix types

the root matrix class mat, type 1 of:

• float, double, std::complex, std::complex, short, int, long, , unsigned versions of short, int, long

in turn, rcpp not support import or export of std::vector<std::string> armadillo. thus, error.

the easiest way find string in case loop through vector , check each element. alternatively, make map , see if key within map.

loop string checking approach:

#include <rcpp.h>  // [[rcpp::export]] std::vector<int> find_string_locs(std::vector<std::string> input_vector, std::string id) {   std::vector<int> id_locs; // setup storage found ids    for(int =0; < input_vector.size(); i++) // loop through input     if(input_vector[i] == id) // check if input matches target       id_locs.push_back(i);      return id_locs; // send locations r (c++ index shift!) }  /***r input_vector = c("stat","toad","stat","rcpp") id = "stat" find_string_locs(input_vector,id) */ 

the output then:

[1] 0 2 

note c++ index shift... starts @ 0 instead of 1 in r.