diff --git a/src/ast/array_decl_plugin.cpp b/src/ast/array_decl_plugin.cpp
index 44c423c09..211c67953 100644
--- a/src/ast/array_decl_plugin.cpp
+++ b/src/ast/array_decl_plugin.cpp
@@ -141,7 +141,7 @@ func_decl * array_decl_plugin::mk_map(func_decl* f, unsigned arity, sort* const*
         std::ostringstream buffer;
         buffer << "map expects to take as many arguments as the function being mapped, "
                << "it was given " << arity << " but expects " << f->get_arity();
-        m_manager->raise_exception(buffer.str().c_str());
+        m_manager->raise_exception(buffer.str());
         return nullptr;
     }
     if (arity == 0) {
@@ -158,14 +158,14 @@ func_decl * array_decl_plugin::mk_map(func_decl* f, unsigned arity, sort* const*
         if (!is_array_sort(domain[i])) {
             std::ostringstream buffer;
             buffer << "map expects an array sort as argument at position " << i;
-            m_manager->raise_exception(buffer.str().c_str());
+            m_manager->raise_exception(buffer.str());
             return nullptr;
         }
         if (get_array_arity(domain[i]) != dom_arity) {
             std::ostringstream buffer;
             buffer << "map expects all arguments to have the same array domain,  "
                    << "this is not the case for argument " << i;
-            m_manager->raise_exception(buffer.str().c_str());
+            m_manager->raise_exception(buffer.str());
             return nullptr;
         }
         for (unsigned j = 0; j < dom_arity; ++j) {
@@ -173,7 +173,7 @@ func_decl * array_decl_plugin::mk_map(func_decl* f, unsigned arity, sort* const*
                 std::ostringstream buffer;
                 buffer << "map expects all arguments to have the same array domain, "
                        << "this is not the case for argument " << i;
-                m_manager->raise_exception(buffer.str().c_str());
+                m_manager->raise_exception(buffer.str());
                 return nullptr;
             }
         }
@@ -181,7 +181,7 @@ func_decl * array_decl_plugin::mk_map(func_decl* f, unsigned arity, sort* const*
             std::ostringstream buffer;
             buffer << "map expects the argument at position " << i 
                    << " to have the array range the same as the function";
-            m_manager->raise_exception(buffer.str().c_str());
+            m_manager->raise_exception(buffer.str());
             return nullptr;
         }
     }
@@ -244,7 +244,7 @@ func_decl* array_decl_plugin::mk_select(unsigned arity, sort * const * domain) {
     if (num_parameters != arity) {
         std::stringstream strm;
         strm << "select requires " << num_parameters << " arguments, but was provided with " << arity << " arguments";
-        m_manager->raise_exception(strm.str().c_str());
+        m_manager->raise_exception(strm.str());
         return nullptr;
     }
     ptr_buffer<sort> new_domain; // we need this because of coercions.
@@ -256,7 +256,7 @@ func_decl* array_decl_plugin::mk_select(unsigned arity, sort * const * domain) {
             std::stringstream strm;
             strm << "domain sort " << sort_ref(domain[i+1], *m_manager) << " and parameter ";
             strm << parameter_pp(parameters[i], *m_manager) << " do not match";
-            m_manager->raise_exception(strm.str().c_str());
+            m_manager->raise_exception(strm.str());
             UNREACHABLE();
             return nullptr;
         }
@@ -284,7 +284,7 @@ func_decl * array_decl_plugin::mk_store(unsigned arity, sort * const * domain) {
         std::ostringstream buffer;
         buffer << "store expects the first argument to be an array taking " << num_parameters+1 
                << ", instead it was passed " << (arity - 1) << "arguments";
-        m_manager->raise_exception(buffer.str().c_str());
+        m_manager->raise_exception(buffer.str());
         UNREACHABLE();
         return nullptr;
     }
diff --git a/src/ast/ast.cpp b/src/ast/ast.cpp
index b84dac136..c73e2f1d8 100644
--- a/src/ast/ast.cpp
+++ b/src/ast/ast.cpp
@@ -1584,8 +1584,8 @@ void ast_manager::raise_exception(char const * msg) {
     throw ast_exception(msg);
 }
 
-void ast_manager::raise_exception(std::string const&  msg) {
-    throw ast_exception(msg.c_str());
+void ast_manager::raise_exception(std::string &&  msg) {
+    throw ast_exception(std::move(msg));
 }
 
 
diff --git a/src/ast/ast.h b/src/ast/ast.h
index 9c6c811b0..1c25ff9ec 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -1574,7 +1574,7 @@ public:
 
     // Equivalent to throw ast_exception(msg)
     Z3_NORETURN void raise_exception(char const * msg);
-    Z3_NORETURN void raise_exception(std::string const& s);
+    Z3_NORETURN void raise_exception(std::string && s);
 
     std::ostream& display(std::ostream& out, parameter const& p);
 
diff --git a/src/ast/ast_smt_pp.cpp b/src/ast/ast_smt_pp.cpp
index ea220f7e7..48daf6988 100644
--- a/src/ast/ast_smt_pp.cpp
+++ b/src/ast/ast_smt_pp.cpp
@@ -951,7 +951,7 @@ void ast_smt_pp::display_smt2(std::ostream& strm, expr* n) {
         strm << "(set-logic " << m_logic << ")\n";
     }
     if (!m_attributes.empty()) {
-        strm << "; " << m_attributes.c_str();
+        strm << "; " << m_attributes;
     }
 
 #if 0
diff --git a/src/ast/bv_decl_plugin.cpp b/src/ast/bv_decl_plugin.cpp
index 738444b3b..4ffd7d6cb 100644
--- a/src/ast/bv_decl_plugin.cpp
+++ b/src/ast/bv_decl_plugin.cpp
@@ -624,7 +624,7 @@ func_decl * bv_decl_plugin::mk_func_decl(decl_kind k, unsigned num_parameters, p
             if (m.get_sort(args[i]) != r->get_domain(i)) {
                 std::ostringstream buffer;
                 buffer << "Argument " << mk_pp(args[i], m) << " at position " << i << " does not match declaration " << mk_pp(r, m);
-                m.raise_exception(buffer.str().c_str());
+                m.raise_exception(buffer.str());
                 return nullptr;
             }
         }
diff --git a/src/ast/datatype_decl_plugin.cpp b/src/ast/datatype_decl_plugin.cpp
index 8bf0abbb3..146c7359f 100644
--- a/src/ast/datatype_decl_plugin.cpp
+++ b/src/ast/datatype_decl_plugin.cpp
@@ -342,7 +342,7 @@ namespace datatype {
                 std::ostringstream buffer;
                 buffer << "second argument to field update should be " << mk_ismt2_pp(rng, m) 
                        << " instead of " << mk_ismt2_pp(domain[1], m);
-                m.raise_exception(buffer.str().c_str());
+                m.raise_exception(buffer.str());
                 return nullptr;
             }
             range = domain[0];
diff --git a/src/ast/dl_decl_plugin.cpp b/src/ast/dl_decl_plugin.cpp
index 01b06518e..43cf50662 100644
--- a/src/ast/dl_decl_plugin.cpp
+++ b/src/ast/dl_decl_plugin.cpp
@@ -54,7 +54,7 @@ namespace datalog {
         }
         std::ostringstream buffer;
         buffer << msg << ", value is not within bound " << low << " <= " << val << " <= " << up;
-        m_manager->raise_exception(buffer.str().c_str());
+        m_manager->raise_exception(buffer.str());
         return false;
     }
 
@@ -676,7 +676,7 @@ namespace datalog {
         }
         std::stringstream strm;
         strm << "sort '" << mk_pp(s, m) << "' is not recognized as a sort that contains numeric values.\nUse Bool, BitVec, Int, Real, or a Finite domain sort";
-        m.raise_exception(strm.str().c_str());
+        m.raise_exception(strm.str());
         return nullptr;
     }
 
diff --git a/src/ast/rewriter/enum2bv_rewriter.cpp b/src/ast/rewriter/enum2bv_rewriter.cpp
index 65250282c..f6f2d6f85 100644
--- a/src/ast/rewriter/enum2bv_rewriter.cpp
+++ b/src/ast/rewriter/enum2bv_rewriter.cpp
@@ -86,7 +86,7 @@ struct enum2bv_rewriter::imp {
         void throw_non_fd(expr* e) {
             std::stringstream strm;
             strm << "unable to handle nested data-type expression " << mk_pp(e, m);
-            throw rewriter_exception(strm.str().c_str());
+            throw rewriter_exception(strm.str());
         }
 
         void check_for_fd(unsigned n, expr* const* args) {
diff --git a/src/ast/rewriter/rewriter_types.h b/src/ast/rewriter/rewriter_types.h
index 094357fed..77ab42b2a 100644
--- a/src/ast/rewriter/rewriter_types.h
+++ b/src/ast/rewriter/rewriter_types.h
@@ -46,7 +46,7 @@ inline br_status unsigned2br_status(unsigned u) {
 
 class rewriter_exception : public default_exception {
 public:                                                
-    rewriter_exception(char const * msg):default_exception(msg) {}
+    rewriter_exception(std::string && msg) : default_exception(std::move(msg)) {}
 };
 
 #endif
diff --git a/src/ast/seq_decl_plugin.cpp b/src/ast/seq_decl_plugin.cpp
index 20e1fb36c..7576e43c0 100644
--- a/src/ast/seq_decl_plugin.cpp
+++ b/src/ast/seq_decl_plugin.cpp
@@ -400,7 +400,7 @@ void seq_decl_plugin::match_right_assoc(psig& sig, unsigned dsz, sort *const* do
         std::ostringstream strm;
         strm << "Unexpected number of arguments to '" << sig.m_name << "' ";
         strm << "at least one argument expected " << dsz << " given";
-        m.raise_exception(strm.str().c_str());
+        m.raise_exception(strm.str());
     }
     bool is_match = true;
     for (unsigned i = 0; is_match && i < dsz; ++i) {
@@ -420,7 +420,7 @@ void seq_decl_plugin::match_right_assoc(psig& sig, unsigned dsz, sort *const* do
         if (range) {
             strm << " and range: " << mk_pp(range, m);
         }
-        m.raise_exception(strm.str().c_str());
+        m.raise_exception(strm.str());
     }
     range_out = apply_binding(binding, sig.m_range);
     SASSERT(range_out);
@@ -434,7 +434,7 @@ void seq_decl_plugin::match(psig& sig, unsigned dsz, sort *const* dom, sort* ran
         std::ostringstream strm;
         strm << "Unexpected number of arguments to '" << sig.m_name << "' ";
         strm << sig.m_dom.size() << " arguments expected " << dsz << " given";
-        m.raise_exception(strm.str().c_str());
+        m.raise_exception(strm.str());
     }
     bool is_match = true;
     for (unsigned i = 0; is_match && i < dsz; ++i) {
@@ -459,13 +459,13 @@ void seq_decl_plugin::match(psig& sig, unsigned dsz, sort *const* dom, sort* ran
             strm << mk_pp(sig.m_dom[i].get(), m) << " ";
         }
 
-        m.raise_exception(strm.str().c_str());
+        m.raise_exception(strm.str());
     }
     if (!range && dsz == 0) {
         std::ostringstream strm;
         strm << "Sort of polymorphic function '" << sig.m_name << "' ";
         strm << "is ambiguous. Function takes no arguments and sort of range has not been constrained";
-        m.raise_exception(strm.str().c_str());
+        m.raise_exception(strm.str());
     }
     range_out = apply_binding(m_binding, sig.m_range);
     SASSERT(range_out);
diff --git a/src/cmd_context/cmd_context.cpp b/src/cmd_context/cmd_context.cpp
index c58453460..9de183ca8 100644
--- a/src/cmd_context/cmd_context.cpp
+++ b/src/cmd_context/cmd_context.cpp
@@ -797,7 +797,7 @@ void cmd_context::insert(symbol const & s, func_decl * f) {
         msg += " '";
         msg += s.str();
         msg += "' (with the given signature) already declared";
-        throw cmd_exception(msg.c_str());
+        throw cmd_exception(std::move(msg));
     }
     if (s != f->get_name()) {
         TRACE("func_decl_alias", tout << "adding alias for: " << f->get_name() << ", alias: " << s << "\n";);
@@ -1142,7 +1142,7 @@ void cmd_context::mk_app(symbol const & s, unsigned num_args, expr * const * arg
             for (unsigned i = 0; i < fs.get_num_entries(); ++i) {
                 buffer << "\ndeclared: " << mk_pp(fs.get_entry(i), m()) << " ";
             }
-            throw cmd_exception(buffer.str().c_str());
+            throw cmd_exception(buffer.str());
         }
         if (well_sorted_check_enabled())
             m().check_sort(f, num_args, args);
diff --git a/src/parsers/smt2/smt2parser.cpp b/src/parsers/smt2/smt2parser.cpp
index bf1e25e57..c103b0276 100644
--- a/src/parsers/smt2/smt2parser.cpp
+++ b/src/parsers/smt2/smt2parser.cpp
@@ -482,7 +482,7 @@ namespace smt2 {
             if (context[0]) msg += ": ";
             msg += "unknown sort '";
             msg += id.str() + "'";
-            throw parser_exception(msg.c_str());
+            throw parser_exception(std::move(msg));
         }
 
         void consume_sexpr() {
@@ -1633,7 +1633,7 @@ namespace smt2 {
         void unknown_var_const_name(symbol id) {
             std::string msg = "unknown constant/variable '";
             msg += id.str() + "'";
-            throw parser_exception(msg.c_str());
+            throw parser_exception(std::move(msg));
         }
 
         rational m_last_bv_numeral; // for bv, bvbin, bvhex
@@ -2431,7 +2431,7 @@ namespace smt2 {
                 buffer << "invalid function definition, sort mismatch. Expcected "
                        << mk_pp(f->get_range(), m()) << " but function body has sort "
                        << mk_pp(m().get_sort(body), m());
-                throw parser_exception(buffer.str().c_str());
+                throw parser_exception(buffer.str());
             }
             m_ctx.insert_rec_fun(f, bindings, ids, body);
         }
diff --git a/src/smt/smt_quantifier.cpp b/src/smt/smt_quantifier.cpp
index 008da06ec..d0ca05ff9 100644
--- a/src/smt/smt_quantifier.cpp
+++ b/src/smt/smt_quantifier.cpp
@@ -173,7 +173,7 @@ namespace smt {
             if (num_instances > 0) {
                 out << "[quantifier_instances] ";
                 out.width(10);
-                out << q->get_qid().str().c_str() << " : ";
+                out << q->get_qid().str() << " : ";
                 out.width(6);
                 out << num_instances << " : ";
                 out.width(3);
diff --git a/src/util/gparams.cpp b/src/util/gparams.cpp
index 9ab3123a2..6b5919f8e 100644
--- a/src/util/gparams.cpp
+++ b/src/util/gparams.cpp
@@ -172,7 +172,7 @@ public:
         }
         for (unsigned i = 0; i < n; i++) {
             if (tmp[i] == '.') {
-                param_name = tmp.substr(i+1).c_str();
+                param_name = tmp.c_str() + i + 1;
                 tmp.resize(i);
                 mod_name   = tmp.c_str();
                 return;