diff --git a/ChangeLog b/ChangeLog
index 94f2992c..726c2ddd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,7 @@
 2017-04-17  Markus Gans  <guru.mail@muenster.de>
 	* Speed up FString::setNumber() by using a decimal 
 	  string lookup table
+	* FString allocates no new memory if the size sufficient.
 
 2017-04-15  Markus Gans  <guru.mail@muenster.de>
 	* Fix unsigned integer underflow in FString::_insert()
diff --git a/src/fstring.cpp b/src/fstring.cpp
index b80ccd0f..dbe3506a 100644
--- a/src/fstring.cpp
+++ b/src/fstring.cpp
@@ -51,7 +51,7 @@ FString::FString (int len, wchar_t c)
   , c_string(0)
 {
   if ( len > 0 )
-    _replace ( FString(uInt(len), c).string );
+    _assign ( FString(uInt(len), c).string );
   else
     initLength(0);
 }
@@ -87,7 +87,7 @@ FString::FString (int len, char c)
   c_string = 0;
 
   if ( len > 0 )
-    _replace ( FString(uInt(len), c).string );
+    _assign ( FString(uInt(len), c).string );
   else
     initLength(0);
 }
@@ -118,7 +118,7 @@ FString::FString (const FString& s)  // copy constructor
   , c_string(0)
 {
   if ( s.string )
-    _replace (s.string);
+    _assign (s.string);
 }
 
 //----------------------------------------------------------------------
@@ -129,7 +129,7 @@ FString::FString (const std::wstring& s)
   , c_string(0)
 {
   if ( ! s.empty() )
-    _replace ( s.c_str() );
+    _assign ( s.c_str() );
 }
 
 //----------------------------------------------------------------------
@@ -140,7 +140,7 @@ FString::FString (const wchar_t* s)
   , c_string(0)
 {
   if ( s )
-    _replace (s);
+    _assign (s);
 }
 
 //----------------------------------------------------------------------
@@ -158,7 +158,7 @@ FString::FString (const std::string& s)
 
   if ( wc_string )
   {
-    _replace( wc_string );
+    _assign( wc_string );
     delete[] wc_string;
   }
 }
@@ -175,7 +175,7 @@ FString::FString (const char* s)
 
   if ( wc_string )
   {
-    _replace( wc_string );
+    _assign (wc_string);
     delete[] wc_string;
   }
 }
@@ -190,7 +190,7 @@ FString::FString (const wchar_t c)
   wchar_t s[2];
   s[0] = c;
   s[1] = L'\0';
-  _replace (s);
+  _assign (s);
 }
 
 //----------------------------------------------------------------------
@@ -203,7 +203,7 @@ FString::FString (const char c)
   wchar_t s[2];
   s[0] = wchar_t(c & 0xff);
   s[1] = L'\0';
-  _replace (s);
+  _assign (s);
 }
 
 //----------------------------------------------------------------------
@@ -222,7 +222,7 @@ FString::~FString()  // destructor
 FString& FString::operator = (const FString& s)
 {
   if ( s )
-    _replace (s.string);
+    _assign (s.string);
   else
     clear();
 
@@ -233,7 +233,7 @@ FString& FString::operator = (const FString& s)
 FString& FString::operator = (const std::wstring& s)
 {
   if ( ! s.empty() )
-    _replace (s.c_str());
+    _assign (s.c_str());
   else
     clear();
 
@@ -244,7 +244,7 @@ FString& FString::operator = (const std::wstring& s)
 const FString& FString::operator = (const wchar_t* s)
 {
   if ( s )
-    _replace (s);
+    _assign (s);
   else
     clear();
 
@@ -258,7 +258,7 @@ FString& FString::operator = (const std::string& s)
 
   if ( wc_string )
   {
-    _replace( wc_string );
+    _assign( wc_string );
     delete[] wc_string;
   }
   else
@@ -274,7 +274,7 @@ const FString& FString::operator = (const char* s)
 
   if ( wc_string )
   {
-    _replace( wc_string );
+    _assign( wc_string );
     delete[] wc_string;
   }
   else
@@ -289,7 +289,7 @@ const FString& FString::operator = (const wchar_t c)
   wchar_t s[2];
   s[0] = c;
   s[1] = L'\0';
-  _replace (s);
+  _assign (s);
   return (*this);
 }
 
@@ -299,7 +299,7 @@ const FString& FString::operator = (const char c)
   wchar_t s[2];
   s[0] = wchar_t(c & 0xff);
   s[1] = L'\0';
-  _replace (s);
+  _assign (s);
   return (*this);
 }
 
@@ -502,7 +502,7 @@ FString& FString::sprintf (const wchar_t* format, ...)
   std::vswprintf (buffer, buf_size, format, args);
   va_end (args);
 
-  _replace (buffer);
+  _assign (buffer);
   return (*this);
 }
 
@@ -532,7 +532,7 @@ FString& FString::sprintf (const char* format, ...)
 
   if ( wc_string )
   {
-    _replace(wc_string);
+    _assign(wc_string);
     delete[] wc_string;
   }
 
@@ -974,7 +974,7 @@ std::vector<FString> FString::split (const FString& delimiter)
 //----------------------------------------------------------------------
 FString& FString::setString (const wchar_t* s)
 {
-  _replace (s);
+  _assign (s);
   return (*this);
 }
 
@@ -985,7 +985,7 @@ FString& FString::setString (const char* s)
 
   if ( wc_string )
   {
-    _replace (wc_string);
+    _assign (wc_string);
     delete[] wc_string;
   }
 
@@ -1023,7 +1023,7 @@ FString& FString::setNumber (long num)
   if ( neg )
     *--s = '-';
 
-  _replace (s);
+  _assign (s);
   return *this;
 }
 
@@ -1043,7 +1043,7 @@ FString& FString::setNumber (uLong num)
   }
   while ( num );
 
-  _replace (s);
+  _assign (s);
   return *this;
 }
 
@@ -1113,7 +1113,7 @@ FString& FString::setFormatedNumber (long num, char separator)
   if ( neg )
     *--s = '-';
 
-  _replace (s);
+  _assign (s);
   return *this;
 }
 
@@ -1142,7 +1142,7 @@ FString& FString::setFormatedNumber (uLong num, char separator)
   }
   while ( num );
 
-  _replace (s);
+  _assign (s);
   return *this;
 }
 
@@ -2212,30 +2212,33 @@ inline void FString::initLength (uInt len)
 }
 
 //----------------------------------------------------------------------
-inline void FString::_replace (const wchar_t* s)
+inline void FString::_assign (const wchar_t* s)
 {
-  if ( string )
-    delete[](string);
-
-  length =  uInt(std::wcslen(s));
-  bufsize = FWDBUFFER + length + 1;
-
-  try
-  {
-    string = new wchar_t[bufsize]();
-  }
-  catch (const std::bad_alloc& ex)
-  {
-    std::cerr << bad_alloc_str << ex.what() << std::endl;
+  if ( s == string )
     return;
-  }
-/*  catch (std::exception& e)
+
+  uInt new_length = uInt(std::wcslen(s));
+
+  if ( ! string || new_length > bufsize - 1 )
   {
-    std::cerr << "not enough memory for a new FString object "
-              << e.what() << std::endl;
-    return;
-  }*/
+    if ( string )
+      delete[](string);
+
+    bufsize = FWDBUFFER + new_length + 1;
+
+    try
+    {
+      string = new wchar_t[bufsize]();
+    }
+    catch (const std::bad_alloc& ex)
+    {
+      std::cerr << bad_alloc_str << ex.what() << std::endl;
+      return;
+    }
+  }
+
   std::wcsncpy (string, s, bufsize);
+  length = new_length;
 }
 
 //----------------------------------------------------------------------
@@ -2517,7 +2520,7 @@ std::istream& operator >> (std::istream& instr, FString& s)
 
   if ( wc_str )
   {
-    s._replace (wc_str);
+    s._assign (wc_str);
     delete[] wc_str;
   }
 
@@ -2538,7 +2541,7 @@ std::wistream& operator >> (std::wistream& instr, FString& s)
 {
   wchar_t buf[FString::INPBUFFER + 1];
   instr.getline (buf, FString::INPBUFFER);
-  s._replace (buf);
+  s._assign (buf);
   return (instr);
 }
 
diff --git a/src/fstring.h b/src/fstring.h
index 23f6515c..b4bf42ca 100644
--- a/src/fstring.h
+++ b/src/fstring.h
@@ -330,7 +330,7 @@ class FString
 
    // Methods
    void     initLength (uInt);
-   void     _replace (const wchar_t*);
+   void     _assign (const wchar_t*);
    void     _insert (uInt, uInt, const wchar_t*);
    void     _remove (uInt, uInt);
    char*    wc_to_c_str (const wchar_t*) const;
diff --git a/test/string-operations.cpp b/test/string-operations.cpp
index 8c3869f8..afe8610d 100644
--- a/test/string-operations.cpp
+++ b/test/string-operations.cpp
@@ -28,58 +28,96 @@ int main (int, char**)
   std::cout << "--------------[ FString test ]-----------------"
             << std::endl;
 
+  // Test: input stream (operator >>)
   FString in;
   std::cout << "     Input: "; std::cin >> in;
   std::cout << "  instream >> " << in << std::endl;
 
+  // Test: output stream (operator <<)
   FString out = L"A test string for 0 \x20ac";
-  std::cout << " outstream << " << out.c_str() << std::endl;
+  std::cout << " outstream << " << out << std::endl;
+
+  // Test: c-string output
   printf ("     c_str:  \"%s\"\n", out.c_str());
 
+  // Test: copy a c++ string
   FString cpp_str( std::string("c++ String") );
   std::cout << "   cpp_str: \"" << cpp_str << "\"" << std::endl;
+
+  // Test: copy a character
   FString ch('c');
   std::cout << "      char: '" << ch << "'" << std::endl;
+
+  // Test: copy a wide character
   FString wch(L'w');
   std::cout << "   wchar_t: '" << wch << "'" << std::endl;
 
+  // Test: utf-8 string
   FString len = "длина́";
   std::cout << "    length: \"" << len << "\" has "
             << len.getLength() << " characters" << std::endl;
 
+  // Test: convert uppercase letter to lowercase
   FString lower = FString(L"InPut").toLower();
   std::wcout << L"   toLower: " << lower << std::endl;
+
+  // Test: convert lowercase letter to uppercase
   FString upper = FString("inPut").toUpper();
   std::cout << "   toUpper: " << upper << std::endl;
 
+  // Test: concatenate two FStrings (operator +)
   FString add1 = FString("FString + ") + FString("FString");
   std::cout << "       add: " << add1 << std::endl;
+
+  // Test: concatenate a FString and a c++ wide string (operator +)
   FString add2 = FString("FString + ") + std::wstring(L"std::wstring");
   std::cout << "       add: " << add2 << std::endl;
+
+  // Test: concatenate a FString and a wide string (operator +)
   FString add3 = FString("FString + ") + const_cast<wchar_t*>(L"wchar_t*");
   std::cout << "       add: " << add3 << std::endl;
+
+  // Test: concatenate a FString and a c++ string (operator +)
   FString add4 = FString("FString + ") + std::string("std::string");
   std::cout << "       add: " << add4 << std::endl;
+
+  // Test: concatenate a FString and a c-string (operator +)
   FString add5 = FString("FString + ") + const_cast<char*>("char*");
   std::cout << "       add: " << add5 << std::endl;
+
+  // Test: concatenate a FString and a wide character (operator +)
   FString add6 = FString("FString + ") + wchar_t(L'w');
   std::cout << "       add: " << add6 << std::endl;
+
+  // Test: concatenate a FString and a character (operator +)
   FString add7 = FString("FString + ") + char('c');
   std::cout << "       add: " << add7 << std::endl;
 
+  // Test: concatenate a character and a FString (operator +)
   FString add8 = 'c' + FString(" + FString");
   std::cout << "       add: " << add8 << std::endl;
+
+  // Test: concatenate a wide character and a FString (operator +)
   FString add9 = L'w' + FString(" + FString");
   std::cout << "       add: " << add9 << std::endl;
+
+  // Test: concatenate a c-string and a FString (operator +)
   FString add10 = const_cast<char*>("char*") + FString(" + FString");
   std::cout << "       add: " << add10 << std::endl;
+
+  // Test: concatenate a c++ string and a FString (operator +)
   FString add11 = std::string("std::string") + FString(" + FString");
   std::cout << "       add: " << add11 << std::endl;
+
+  // Test: concatenate a wide string and a FString (operator +)
   FString add12 = const_cast<wchar_t*>(L"wchar_t*") + FString(" + FString");
   std::cout << "       add: " << add12 << std::endl;
+
+  // Test: concatenate a c++ wide string and a FString (operator +)
   FString add13 = std::wstring(L"std::wstring") + FString(" + FString");
   std::cout << "       add: " << add13 << std::endl;
 
+  // Test: compare operators ==, <=, <, >=, >, !=
   FString cmp = "compare";
 
   if ( cmp == FString("compare") )
@@ -112,6 +150,7 @@ int main (int, char**)
   else
     std::cout << "       cmp: != Not Ok" << std::endl;
 
+  // Test: split a string with a delimiter and returns a vector (array)  
   FString split_str = "a,b,c,d";
   std::cout << "     split: \""
             << split_str << "\" into substrings ->";
@@ -124,10 +163,13 @@ int main (int, char**)
 
   std::cout << std::endl;
 
+  // Test: format a string with sprintf
   FString formatStr = "";
   std::cout << " formatted: "
             << formatStr.sprintf("sqrt(%d) = %d", 16, 4)
             << std::endl;
+
+  // Test: convert a string to a unsigned long interger
   try
   {
     uLong ulong_num = FString("123456789").toULong();
@@ -142,6 +184,7 @@ int main (int, char**)
     std::cerr << "Arithmetic error: " << ex.what() << std::endl;
   }
 
+  // Test: convert a string to a signed long interger
   try
   {
     long long_num = FString("-9876543210").toLong();
@@ -156,6 +199,7 @@ int main (int, char**)
     std::cerr << "Arithmetic error: " << ex.what() << std::endl;
   }
 
+  // Test: convert a string to a double value
   std::setlocale(LC_NUMERIC, "C");
 
   try
@@ -175,6 +219,7 @@ int main (int, char**)
     std::cerr << "Arithmetic error: " << ex.what() << std::endl;
   }
 
+  // Test: convert integer and double value to a string 
   FString num1, num2, num3;
   num1.setNumber(137);
   num2.setNumber(-512);
@@ -186,6 +231,7 @@ int main (int, char**)
   std::cout << " setNumber:  "
             << num3 << " (long double)" << std::endl;
 
+  // Test: convert and format a integer number with thousand separator
   std::setlocale (LC_NUMERIC, "");
   FString fnum1, fnum2;
 #if defined(__LP64__) || defined(_LP64)
@@ -202,22 +248,33 @@ int main (int, char**)
   std::cout << "setFormatedNumber: "
             << fnum2 << " (signed)"   << std::endl;
 
+  // Test: remove whitespace from the end of a string
   FString trim_str = "  A string \t";
   std::wcout << "    rtrim: \""
              << trim_str.rtrim() << "\"" << std::endl;
+
+  // Test: remove whitespace from the beginning of a string
   std::cout << "    ltrim: \""
             << trim_str.ltrim() << "\"" << std::endl;
+
+  // Test: remove whitespace from the beginning and end of a string
   std::cout << "     trim: \""
             << trim_str.trim()  << "\"" << std::endl;
 
+  // Test: 11 characters from the left of the string
   FString alphabet = "a b c d e f g h i j k l m n o p q r s t u v w x y z";
   std::cout << "     left: \""
             << alphabet.left(11)   << "\"" << std::endl;
+
+  // Test: extract a substring of 27 characters from position 12
   std::cout << "      mid: \""
             << alphabet.mid(13,27) << "\"" << std::endl;
+
+  // Test: 11 characters from the right of the string
   std::cout << "    right: \""
             << alphabet.right(11)  << "\"" << std::endl;
 
+  // Test: insert a string at index position 7
   FString insert_str = "I am a string";
 
   try
@@ -230,7 +287,8 @@ int main (int, char**)
     std::cerr << "Out of Range error: " << ex.what() << std::endl;
   }
 
-  FString index(5); // a string with five characters
+  // Test: get character access at a specified index position
+  FString index(5); // string with five characters
   index = "index";
 
   try
@@ -245,6 +303,7 @@ int main (int, char**)
     std::cerr << "Out of Range error: " << ex.what() << std::endl;
   }
 
+  // Test: character access with std::iterator
   FString stringIterator = "iterator";
   FString::iterator iter;
   iter = stringIterator.begin();
@@ -260,14 +319,17 @@ int main (int, char**)
             << "', back='" << char(stringIterator.back())
             << "')" << std::endl;
 
+  // Test: overwrite string at position 10 with "for t"
   FString overwrite_std = "Overwrite the rest";
   std::cout << "overwrite: "
             << overwrite_std.overwrite("for t", 10) << std::endl;
 
+  // Test: remove 2 characters at position 7
   FString remove_std = "A fast remove";
   std::cout << "   remove: "
             << remove_std.remove(7,2) << std::endl;
 
+  // Test: includes a substring (positive test)
   FString include_std = "string";
 
   if ( include_std.includes("ring") )
@@ -279,6 +341,7 @@ int main (int, char**)
               << include_std << "\" includes no \"ring\" "
               << std::endl;
 
+  // Test: includes a substring (negativ test)
   if ( include_std.includes("data") )
     std::cout << " includes: \""
               << include_std << "\" includes \"data\" "
@@ -288,19 +351,23 @@ int main (int, char**)
               << include_std << "\" includes no \"data\" "
               << std::endl;
 
+  // Test: find and replace a substring
   FString source_str = "computer and software";
   FString replace_str = source_str.replace("computer", "hard-");
   std::cout << "  replace: "
             << replace_str << std::endl;
 
+  // Test: convert tabs to spaces
   FString tab_str = "1234\t5678";
   std::cout << "      tab: "
             << tab_str.expandTabs() << std::endl;
 
+  // Test: backspaces remove characters in the string
   FString bs_str = "t\b\bTesT\bt";
   std::cout << "backspace: "
             << bs_str.removeBackspaces() << std::endl;
 
+  // Test: delete characters remove characters in the string
   FString del_str = "apple \177\177\177pietree";
   std::cout << "   delete: "
             << del_str.removeDel() << std::endl;