changes to exceptions that returned pointer to temporary object

SpMat.h

@@ -39,10 +39,10 @@ class SpMatException: public std::exception
 private:
   std::string m_msg;
 public:
-  SpMatException(const std::string& msg) throw(): m_msg(msg) {}
+  SpMatException(const std::string& msg) throw(): m_msg(std::string("SpMat::")+msg) {}
 
   virtual const char * what() const throw() {
-    return std::string("SpMat::" + m_msg).c_str();
+    return(m_msg.c_str());
   }
 
   ~SpMatException() throw() {}

bfmatrix.h

@@ -42,10 +42,10 @@ class BFMatrixException: public std::exception
 private:
   std::string m_msg;
 public:
-  BFMatrixException(const std::string& msg) throw(): m_msg(msg) {}
+  BFMatrixException(const std::string& msg) throw(): m_msg(std::string("BFMatrix::")+msg) {}
 
   virtual const char * what() const throw() {
-    return std::string("BFMatrix::" + m_msg).c_str();
+    return(m_msg.c_str());
   }
 
   ~BFMatrixException() throw() {}

nonlin.h

@@ -65,10 +65,10 @@ class NonlinException: public std::exception
 private:
   std::string m_msg;
 public:
-  NonlinException(const std::string& msg) throw(): m_msg(msg) {}
+  NonlinException(const std::string& msg) throw(): m_msg(std::string("Nonlin: msg=")+msg) {}
 
   virtual const char * what() const throw() {
-    return std::string("Nonlin: msg=" + m_msg).c_str();
+    return(m_msg.c_str());
   }
 
   ~NonlinException() throw() {}