fix string.push_front() (#230)

ChangeLog

@@ -1,3 +1,9 @@
+2015-01-16  Kevin Ushey  <kevinushey@gmail.com>
+
+        * inst/include/Rcpp/String.h: fix push_front()
+        * inst/unitTests/runit.String.R: test
+        * inst/unitTests/cpp/String.cpp: test
+
 2015-01-15  Kevin Ushey  <kevinushey@gmail.com>
 
         * inst/include/Rcpp/platform/sysmacros.h: remove leaked macros

inst/include/Rcpp/String.h

@@ -292,7 +292,7 @@ namespace Rcpp {
 
         inline String& push_front( const char* s){
             if( is_na() ) return *this ;
-            setBuffer() ; valid = false ; buffer += s ;
+            setBuffer() ; valid = false ; buffer = s + buffer;
             return *this ;
         }
         inline String& push_front( const std::string& s){

inst/unitTests/cpp/String.cpp

@@ -56,3 +56,8 @@ List test_compare_Strings( String aa, String bb ){
         ) ;
 }
 
+// [[Rcpp::export]]
+String test_push_front(String x) {
+    x.push_front("abc");
+    return x;
+}

inst/unitTests/runit.String.R

@@ -49,5 +49,9 @@ if (.runThisTest) {
             )
         checkEquals( res, target )
     }
-
+
+    test.push.front <- function() {
+        res <- test_push_front("def")
+        checkIdentical(res, "abcdef")
+    }
 }