strutils: new functions stripTrailingNewlines() and stripTrailingNewlines_inplace()

simgear/misc/strutils.cxx

@@ -238,6 +238,35 @@ namespace simgear {
 	    return do_strip( s, BOTHSTRIP );
 	}
 
+        void
+        stripTrailingNewlines_inplace(string& s)
+        {
+          // The following (harder to read) implementation is much slower on
+          // my system (g++ 6.2.1 on Debian): 11.4 vs. 3.9 seconds on
+          // 50,000,000 iterations performed on a short CRLF-terminated
+          // string---and it is even a bit slower (12.9 seconds) with
+          // std::next(it) instead of (it+1).
+          //
+          // for (string::reverse_iterator it = s.rbegin();
+          //      it != s.rend() && (*it == '\r' || *it == '\n'); /* empty */) {
+          //   it = string::reverse_iterator(s.erase( (it+1).base() ));
+          // }
+
+          // Simple and fast
+          while (!s.empty() && (s.back() == '\r' || s.back() == '\n')) {
+            s.pop_back();
+          }
+        }
+
+        string
+        stripTrailingNewlines(const string& s)
+        {
+          string res = s;
+          stripTrailingNewlines_inplace(res);
+
+          return res;
+        }
+
 	string
 	rpad( const string & s, string::size_type length, char c )
 	{

simgear/misc/strutils.hxx

@@ -70,6 +70,24 @@ namespace simgear {
 	std::string rstrip( const std::string& s );
 	std::string strip( const std::string& s );
 
+	/**
+         * Return a new string with any trailing \r and \n characters removed.
+         * Typically useful to clean a CR-terminated line obtained from
+         * std::getline() which, upon reading CRLF (\r\n), discards the Line
+         * Feed character (\n) but leaves the Carriage Return (\r) in the
+         * string.
+         * @param s Input string
+         * @return The cleaned string
+         */
+        std::string stripTrailingNewlines(const std::string& s);
+
+	/**
+         * Strip any trailing \r and \n characters from a string.
+         * Should have slightly less overhead than stripTrailingNewlines().
+         * @param s Input string (modified in-place)
+         */
+        void stripTrailingNewlines_inplace(std::string& s);
+
         /**
          * Right-padding of a string to a given length
          * @param s String to pad

simgear/misc/strutils_test.cxx

@@ -25,6 +25,34 @@ void test_strip()
   SG_CHECK_EQUAL(strutils::strip("\t \na \t b\r \n "), "a \t b");
 }
 
+void test_stripTrailingNewlines()
+{
+  SG_CHECK_EQUAL(strutils::stripTrailingNewlines("\rfoobar\n\r\n\n\r\r"),
+                 "\rfoobar");
+  SG_CHECK_EQUAL(strutils::stripTrailingNewlines("\rfoobar\r"), "\rfoobar");
+  SG_CHECK_EQUAL(strutils::stripTrailingNewlines("\rfoobar"), "\rfoobar");
+  SG_CHECK_EQUAL(strutils::stripTrailingNewlines(""), "");
+}
+
+void test_stripTrailingNewlines_inplace()
+{
+  string s = "\r\n\r\rfoo\n\r\rbar\n\r\n\r\r\n\r\r";
+  strutils::stripTrailingNewlines_inplace(s);
+  SG_CHECK_EQUAL(s, "\r\n\r\rfoo\n\r\rbar");
+
+  s = "\rfoobar\r";
+  strutils::stripTrailingNewlines_inplace(s);
+  SG_CHECK_EQUAL(s, "\rfoobar");
+
+  s = "\rfoobar";
+  strutils::stripTrailingNewlines_inplace(s);
+  SG_CHECK_EQUAL(s, "\rfoobar");
+
+  s = "";
+  strutils::stripTrailingNewlines_inplace(s);
+  SG_CHECK_EQUAL(s, "");
+}
+
 void test_starts_with()
 {
   SG_VERIFY(strutils::starts_with("banana", "ban"));
@@ -148,6 +176,8 @@ void test_error_string()
 int main(int argc, char* argv[])
 {
     test_strip();
+    test_stripTrailingNewlines();
+    test_stripTrailingNewlines_inplace();
     test_starts_with();
     test_ends_with();
     test_simplify();