Chapter 15 String

String is a scalar type corresponding to the element of CharacterVector. String can also handle NA values (NA_STRING) which are not supported by the C character string char* and the C++ string std::string.

15.1 Creating String object

There are roughly　three ways to create a String object, as follows. The first method is to create from a C/C++ string, the second is to create it from another String object, and the third is to create it from one element of a CharacterVector.

// Creating from C string
String s("X"); // "X"

// Creating from Rcpp String
String s(str);

//Creating from single element of CharacterVector object
String s(char_vec[0])

15.2 Operators

The += operator is defined in String type. This allows you to combine another string object at the end of the string. (Note that the + operator is not defined)

// Creating String object
String s("A");

// Conbining a string
s += "B";

Rcout << s << "\n"; // "AB"

15.3 Member functions

Note: The member functions replace_first(), replace_last(), replace_all() do not just return the replaced character string, but instead rewrite the value of this object.

15.3.1 replace_first( str, new_str )

Replace first substring that matches the string str with the string new_str.

15.3.2 replace_last( str, new_str )

Replace last substring that matches the string str with the string new_str.

15.3.3 replace_all( str, new_str )

Replace all substrings that matches the string str with the string new_str.

15.3.4 push_back(str)

Combine the string str to the end of this String object. (Same as += operator)

15.3.5 push_front(str)

Combine the string str at the beginning of this String object.

15.3.6 set_na()

Set NA value to this String object.

15.3.7 get_cstring()

Convert the string of this String object into a C character string constant (const char*) and return it.

15.3.8 get_encoding()

Returns the character encoding. The encoding is represented by cetype_t.

15.3.9 set_encoding(enc)

Set the character encoding specified by cetype_t.

15.3.10 Code example

// [[Rcpp::export]]
void rcpp_replace(){

    // Replace only at the first occurrence of "ab"
    String s("abcdabcd");
    s.replace_first("ab", "AB");
    Rcout << s.get_cstring() << "\n"; // ABcdabcd

    // Replace only at the last occurrence of "ab"
    s="abcdabcd";
    s.replace_last("ab", "AB");
    Rcout << s.get_cstring() << "\n"; // abcdABcd

    // Replace every occurrence of "ab"
    s="abcdabcd";
    s.replace_all("ab", "AB");
    Rcout << s.get_cstring() << "\n"; // ABcdABcd
}