use std::string_view for unicode.h functions

src/util/unicode.cpp

@@ -61,7 +61,7 @@ std::wstring widen(const char *s)
 #endif
 }
 
-std::string narrow(const std::wstring &s)
+std::string narrow(std::wstring_view s)
 {
 #ifdef _WIN32
 
@@ -84,7 +84,7 @@ std::string narrow(const std::wstring &s)
 #endif
 }
 
-std::wstring widen(const std::string &s)
+std::wstring widen(std::string_view s)
 {
 #ifdef _WIN32
 
@@ -188,7 +188,7 @@ static void utf16_append_code(unsigned int code, std::wstring &result)
 /// \par parameters: String in UTF-8 format
 /// \return String in UTF-16 format. The encoding follows the endianness of the
 ///   architecture iff swap_bytes is true.
-std::wstring utf8_to_utf16_native_endian(const std::string &in)
+std::wstring utf8_to_utf16_native_endian(std::string_view in)
 {
   std::wstring result;
   result.reserve(in.size());
@@ -202,7 +202,7 @@ std::wstring utf8_to_utf16_native_endian(const std::string &in)
 /// Convert UTF8-encoded string to UTF-32 with architecture-native endianness.
 /// \par parameters: String in UTF-8 format
 /// \return String in UTF-32 format.
-std::u32string utf8_to_utf32(const std::string &utf8_str)
+std::u32string utf8_to_utf32(std::string_view utf8_str)
 {
   std::u32string result;
   result.reserve(utf8_str.size());
@@ -347,7 +347,7 @@ std::string utf16_native_endian_to_java(const char16_t ch)
 /// \param in: String in UTF-16 (native endianness) format
 /// \return Valid Java string literal in US-ASCII format, with \\uxxxx escapes
 /// for other characters
-std::string utf16_native_endian_to_java_string(const std::wstring &in)
+std::string utf16_native_endian_to_java_string(std::wstring_view in)
 {
   std::ostringstream result;
   const std::locale loc;

src/util/unicode.h

@@ -11,15 +11,16 @@ Author: Daniel Kroening, kroening@kroening.com
 
 #include <algorithm>
 #include <string>
+#include <string_view>
 #include <vector>
 
 // we follow the ideas suggested at
 // http://www.utf8everywhere.org/
 
-std::string narrow(const wchar_t *s);
-std::wstring widen(const char *s);
-std::string narrow(const std::wstring &s);
-std::wstring widen(const std::string &s);
+std::string narrow(const wchar_t *);
+std::wstring widen(const char *);
+std::string narrow(std::wstring_view);
+std::wstring widen(std::string_view);
 
 // This removes the need to have a #ifdef whenever using std::fstream.
 #ifdef _WIN32
@@ -28,16 +29,16 @@ std::wstring widen(const std::string &s);
 #  define widen_if_needed(s) (s)
 #endif
 
-std::string utf32_native_endian_to_utf8(const std::basic_string<char32_t> &s);
+std::string utf32_native_endian_to_utf8(const std::basic_string<char32_t> &);
 
 /// \param utf8_str: UTF-8 string
 /// \return UTF-32 encoding of the string
-std::u32string utf8_to_utf32(const std::string &utf8_str);
+std::u32string utf8_to_utf32(std::string_view utf8_str);
 
-std::wstring utf8_to_utf16_native_endian(const std::string &in);
-std::string utf16_native_endian_to_java(const char16_t ch);
-std::string utf16_native_endian_to_java(const std::wstring &in);
-std::string utf16_native_endian_to_java_string(const std::wstring &in);
+std::wstring utf8_to_utf16_native_endian(std::string_view);
+std::string utf16_native_endian_to_java(const char16_t);
+std::string utf16_native_endian_to_java(std::wstring_view);
+std::string utf16_native_endian_to_java_string(std::wstring_view);
 
 std::vector<std::string> narrow_argv(int argc, const wchar_t **argv_wide);