diff --git a/src/debug.h b/src/debug.h
index 295c665..f7752fa 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -41,5 +41,5 @@ static void dump8(unsigned char* to_dump, unsigned long offset,
 }
 
 //
-#define TRACE(x) cout<<__FUNCTION__<<": "<<(x)<<endl;
-#define TRACE2(x, y) cout<<__FUNCTION__<<": "<<(x)<<(y)<<endl;
+#define TRACE(...) do { (void)printf(__FUNCTION__ ": "); (void)printf(__VA_ARGS__); } while(0)
+
diff --git a/src/rpn-general.h b/src/rpn-general.h
index 5da11a4..0c5b4ec 100644
--- a/src/rpn-general.h
+++ b/src/rpn-general.h
@@ -14,15 +14,13 @@ void good_bye()
 void help()
 {
     // software name
-    cout<<endl;
-    cout<<ATTR_BOLD<<uname<<ATTR_OFF<<endl;
-    cout<<endl;
+    printf("\n" ATTR_BOLD "%s" ATTR_OFF "\n", uname);
 
     // description
-    cout<<description<<endl<<endl;
+    printf("%s\n\n", description);
 
     // syntax
-    cout<<syntax<<endl;
+    printf("%s\n", syntax);
 
     // keywords
     for(unsigned int i=0; i<sizeof(_keywords)/sizeof(_keywords[0]); i++)
@@ -31,30 +29,30 @@ void help()
         {
             // titles in bold
             if (_keywords[i].type==cmd_undef)
-                cout<<ATTR_BOLD;
+                printf(ATTR_BOLD);
             // show title or keyword + comment
-            cout<<_keywords[i].name<<"\t"<<_keywords[i].comment<<endl;
+            printf("%s\t%s\n", _keywords[i].name, _keywords[i].comment.c_str());
             if (_keywords[i].type==cmd_undef)
-                cout<<ATTR_OFF;
+                printf(ATTR_OFF);
         }
     }
-    cout<<endl;
+    printf("\n");
 
     // show mode
-    cout<<"Current float mode is ";
+    printf("Current float mode is ");
     switch(number::s_mode)
     {
-        case number::std: cout << "'std'"; break;
-        case number::fix: cout << "'fix'"; break;
-        case number::sci: cout << "'sci'"; break;
-        default: cout << "unknown"; break;
+        case number::std: printf("'std'"); break;
+        case number::fix: printf("'fix'"); break;
+        case number::sci: printf("'sci'"); break;
+        default: printf("unknown"); break;
     }
-    cout<<" with "<<number::s_current_precision<<" digits"<<endl;
+    printf(" with %d digits\n", number::s_current_precision);
 
     // calc precision and rounding mode
-    cout<<"Current floating point precision is "<<(int)s_mpfr_prec<<" bits"<<endl;
-    cout<<"Current rounding mode is '"<<s_mpfr_rnd_str[s_mpfr_rnd]<<"'"<<endl;
-    cout<<endl<<endl;
+    printf("Current floating point precision is %d bits\n", (int)s_mpfr_prec);
+    printf("Current rounding mode is '%s'\n", s_mpfr_rnd_str[s_mpfr_rnd]);
+    printf("\n\n");
 }
 
 void std()
diff --git a/src/rpn-store.h b/src/rpn-store.h
index a26e421..8f33eb2 100644
--- a/src/rpn-store.h
+++ b/src/rpn-store.h
@@ -37,33 +37,28 @@ void edit(void)
 {
     MIN_ARGUMENTS(1);
 
-    stringstream out;
-
-    if (((object*)_stack->back())->_type == cmd_number)
+    FILE* tmp = tmpfile();
+    if (tmp != NULL)
     {
-        switch(number::s_mode)
+        // re-write stack objet in a stream
+        ((object*)_stack->pop_back())->show(tmp);
+
+        // edit: stuff chars using readline facility
+        int len = (int)ftell(tmp);
+        rewind(tmp);
+        for(int i=0;i<len;i++)
         {
-        case number::std:
-            out.precision(number::s_current_precision);
-            out.unsetf(ios_base::floatfield);
-            break;
-        case number::fix:
-            out << setprecision(number::s_current_precision) << fixed;
-            break;
-        case number::sci:
-            out << setprecision(number::s_current_precision) << scientific;
-            break;
+            char readc;
+            if (fread(&readc, 1, 1, tmp) == 1)
+                rl_stuff_char(readc);
+            else
+            {
+                ERR_CONTEXT(ret_runtime_error);
+                break;
+            }
         }
+        fclose(tmp);
     }
-
-    // re-write stack objet in a stream
-    ((object*)_stack->pop_back())->show(out);
-
-    // edit: stuff chars using readline facility
-    string str = out.str();
-
-    for(int i=0;i<str.size();i++)
-        rl_stuff_char(str[i]);
 }
 
 // carefull : this is not a langage command
@@ -129,25 +124,25 @@ void vars(void)
     for (int i=0; i<(int)_global_heap->size(); i++)
     {
         (void)_global_heap->get_by_index(i, name, obj, size);
-        cout<<"var "<<i+1<<": name '"<<name<<"', type "<<cmd_type_string[obj->_type]<<", value ";
+        printf("var %d: name '%s', type %s, value ", i+1, name.c_str(), cmd_type_string[obj->_type]);
         obj->show();
-        cout<<endl;
+        printf("\n");
     }
     if (_parent_local_heap != NULL)
     {
         for (int i=0; i<(int)_parent_local_heap->size(); i++)
         {
             (void)_parent_local_heap->get_by_index(i, name, obj, size);
-            cout<<"local var "<<i+1<<": name '"<<name<<"', type "<<cmd_type_string[obj->_type]<<", value ";
+            printf("local var %d: name '%s', type %s, value ", i+1, name.c_str(), cmd_type_string[obj->_type]);
             obj->show();
-            cout<<endl;
+            printf("\n");
         }
     }
     for (int i=0; i<(int)_local_heap.size(); i++)
     {
         (void)_local_heap.get_by_index(i, name, obj, size);
-        cout<<"local var "<<i+1<<": name '"<<name<<"', type "<<cmd_type_string[obj->_type]<<", value ";
+        printf("local var %d: name '%s', type %s, value ", i+1, name.c_str(), cmd_type_string[obj->_type]);
         obj->show();
-        cout<<endl;
+        printf("\n");
     }
 }
diff --git a/src/rpn-string.h b/src/rpn-string.h
index 27846d9..029c3e0 100644
--- a/src/rpn-string.h
+++ b/src/rpn-string.h
@@ -6,15 +6,23 @@ void instr()
     if (_stack->get_type(0) != cmd_string)
     {
         // write the object in stack(0) in a string and remove this obj
-        stringstream out;
-        ((object*)_stack->pop_back())->show(out);
+        FILE* tmp = tmpfile();
+        if (tmp != NULL)
+        {
+            ((object*)_stack->pop_back())->show(tmp);
 
-        // reserve the correct size in stack
-        unsigned int str_size = (unsigned int)out.str().size();
-        ostring* str = (ostring*)_stack->allocate_back(str_size+1+sizeof(ostring), cmd_string);
+            // reserve the correct size in stack
+            unsigned int str_size = (unsigned int)ftell(tmp);
+            ostring* str = (ostring*)_stack->allocate_back(str_size+1+sizeof(ostring), cmd_string);
+            str->_size = str_size;
 
-        // fill the obj
-        str->set(out.str().c_str(), str_size);
+            // fill the obj
+            if (fread(str->_value, str_size, 1, tmp) != str_size)
+                ERR_CONTEXT(ret_runtime_error);
+            fclose(tmp);
+        }
+        else
+            ERR_CONTEXT(ret_runtime_error);
     }
 }
 
@@ -29,8 +37,6 @@ void strout()
 
     // make program from string in stack level 1
     if (program::parse(entry.c_str(), prog) == ret_ok)
-    {
         // run it
         prog.run(*_stack, *_global_heap, &_local_heap);
-    }
 }
diff --git a/src/rpn-test-core.h b/src/rpn-test-core.h
index 3643b9b..0282edf 100644
--- a/src/rpn-test-core.h
+++ b/src/rpn-test-core.h
@@ -36,22 +36,19 @@ void program::test()
         {
             getline(test_file, entry);
             if (entry.substr(0,2)=="##")
-            {
-                cout << entry;
-                cout << endl;
-            }
+                printf("%s\n", entry.c_str());
             else if (entry.substr(0,2)=="# ")
             {
                 // indicates the status of previous test
                 if (failed == false && tests > 0)
-                    cout<<FG_GREEN<<" PASSED"<<COLOR_OFF<<endl;
+                    printf(FG_GREEN " PASSED" COLOR_OFF "\n");
                 failed = false;
 
                 // read a test title
                 test_title = entry;
                 is_first_step = true;
                 is_test_error_shown = false;
-                cout << test_title;
+                printf("%s", test_title.c_str());
             }
             // treat "-> stack size should be "
             else if (entry.find(stack_size, 0) == 0)
@@ -72,15 +69,15 @@ void program::test()
                     // count fail test and step
                     if (!is_test_error_shown)
                     {
-                        cout<<FG_RED<<" FAIL"<<COLOR_OFF<<endl;
+                        printf(FG_RED " FAIL" COLOR_OFF "\n");
                         tests_failed++;
                         is_test_error_shown = true;
                     }
                     steps_failed++;
 
                     // show failure
-                    cout<<"\t"<<entry<<endl;
-                    cout<<"\tbut real stack size is "<<FG_RED<<stk.size()<<COLOR_OFF<<endl;
+                    printf("\t%s\n", entry.c_str());
+                    printf("\tbut real stack size is " FG_RED "%d" COLOR_OFF "\n", stk.size());
                     failed = true;
                 }
                 is_first_step = false;
@@ -97,32 +94,51 @@ void program::test()
                 string stack_should_be = entry.substr(stack_value.size());
                 string stack_is;
                 string tmp;
-                for (int i = 0; i < (int)stk.size(); i++)
+                
+                FILE* tmp_file = tmpfile();
+                if (tmp_file != NULL)
                 {
-                    stringstream os;
-                    if (i > 0)
-                        stack_is += ", ";
-                    ((object*)stk.seq_obj(i))->show(os);
-                    getline(os, tmp);
-                    stack_is += tmp;
-                }
-                if (stack_is != stack_should_be)
-                {
-                    // count fail test and step
-                    if (!is_test_error_shown)
+                    char* line;
+                    for (int i = 0; i < (int)stk.size(); i++)
                     {
-                        cout<<FG_RED<<" FAIL"<<COLOR_OFF<<endl;
-                        tests_failed++;
-                        is_test_error_shown = true;
-                    }
-                    steps_failed++;
+                        if (i > 0)
+                            stack_is += ", ";
 
-                    // show failure
-                    cout<<"\t"<<entry<<endl;
-                    cout<<"\tbut real stack is "<<FG_RED<<stack_is<<COLOR_OFF<<endl;
-                    failed = true;
+                        rewind(tmp_file);
+                        ((object*)stk.seq_obj(i))->show(tmp_file);
+                        line = NULL;
+                        if (getline(&line, NULL, tmp_file) >=0)
+                        {
+                            stack_is += line;
+                            free(line);
+                        }
+                        else
+                        {
+                            ERR_CONTEXT(ret_runtime_error);
+                            break;
+                        }
+                    }
+                    if (stack_is != stack_should_be)
+                    {
+                        // count fail test and step
+                        if (!is_test_error_shown)
+                        {
+                            printf(FG_RED " FAIL" COLOR_OFF "\n");
+                            tests_failed++;
+                            is_test_error_shown = true;
+                        }
+                        steps_failed++;
+
+                        // show failure
+                        printf("\t%s\n", entry.c_str());
+                        printf("\tbut real stack size is " FG_RED "%s" COLOR_OFF "\n", stack_is.c_str());
+                        failed = true;
+                    }
+                    is_first_step = false;
+                    fclose(tmp_file);
                 }
-                is_first_step = false;
+                else
+                    ERR_CONTEXT(ret_runtime_error);
             }
             // treat "-> error should be "
             else if (entry.find(cmd_error, 0) == 0)
@@ -142,15 +158,15 @@ void program::test()
                     // count fail test and step
                     if (!is_test_error_shown)
                     {
-                        cout<<FG_RED<<" FAIL"<<COLOR_OFF<<endl;
+                        printf(FG_RED " FAIL" COLOR_OFF "\n");
                         tests_failed++;
                         is_test_error_shown = true;
                     }
                     steps_failed++;
 
                     // show failure
-                    cout<<"\t"<<entry<<endl;
-                    cout<<"\tbut last error is "<<FG_RED<<last_err<<COLOR_OFF<<endl;
+                    printf("\t%s\n", entry.c_str());
+                    printf("\tbut last error is " FG_RED "%d" COLOR_OFF "\n", last_err);
                     failed = true;
                 }
                 is_first_step = false;
@@ -177,27 +193,27 @@ void program::test()
         // last test
         // indicates the status of previous test
         if (failed == false && tests > 0)
-            cout << FG_GREEN << " PASSED" << COLOR_OFF << endl;
+            printf(FG_GREEN " PASSED" COLOR_OFF "\n");
 
         // cerr back
         cerr.rdbuf(cerr_old_buffer);
         
         // conclusion
-        cout<<endl<<"Run "<<tests<<" tests: "<<tests-tests_failed<<" passed, ";
+        printf("\nRun %d tests: %d passed, ", tests, tests-tests_failed);
         if(tests_failed>0)
-            cout<<FG_RED;
-        cout<<tests_failed<<" failed";
+            printf(FG_RED);
+        printf("%d failed", tests_failed);
         if(tests_failed>0)
-            cout<<COLOR_OFF;
+            printf(COLOR_OFF);
         
-        cout<<" ("<<steps<<" steps: "<<steps-steps_failed<<" passed, ";
+        printf(" (%d steps:  %d passed, ", steps, steps-steps_failed);
         if(steps_failed>0)
-            cout<<FG_RED;
-        cout<<steps_failed<<" failed";
+            printf(FG_RED);
+        printf("%d failed", steps_failed);
         if(steps_failed>0)
-            cout<<COLOR_OFF;
-        cout<<")"<<endl;
+            printf(COLOR_OFF);
+        printf(")\n");
     }
     else
-        cerr << "test file '"<<test_filename<<"' not found" << endl;
+        fprintf(stderr, "test file '%s' not found\n", test_filename.c_str());
 }
diff --git a/src/rpn.cpp b/src/rpn.cpp
index 383004b..e0a1ae7 100644
--- a/src/rpn.cpp
+++ b/src/rpn.cpp
@@ -143,7 +143,7 @@ struct object
 
     //
     unsigned int size() { return _size; }
-    void show(ostream& stream = cout);
+    void show(FILE* stream = stdout);
 };
 
 struct number : public object
@@ -344,42 +344,38 @@ struct branch : public object
     char _value[0];
 };
 
-void object::show(ostream& stream)
+void object::show(FILE* stream)
 {
-    //char buffer[512];
-
     switch(_type)
     {
     case cmd_number:
         switch(((number*)this)->_representation)
         {
             case number::dec:
-                (void)mpfr_printf(s_mpfr_printf_format.c_str(), ((number*)this)->_value.mpfr);
-                //stream<<buffer;
+                mpfr_fprintf(stream, s_mpfr_printf_format.c_str(), ((number*)this)->_value.mpfr);
                 break;
             case number::hex:
-                (void)mpfr_printf(string(MPFR_FORMAT_HEX).c_str(), ((number*)this)->_value.mpfr);                
-                //stream<<buffer;
+                mpfr_fprintf(stream, string(MPFR_FORMAT_HEX).c_str(), ((number*)this)->_value.mpfr);                
                 break;
             case number::bin:
-                cout<<"<binary representation TODO>";
+                fprintf(stream, "<binary representation TODO>\n");
         }
         break;
     case cmd_string:
-        stream << "\"" << ((ostring*)this)->_value << "\"";
+        fprintf(stream, "\"%s\"", ((ostring*)this)->_value);
         break;
     case cmd_program:
-        stream << "<<" << ((oprogram*)this)->_value << ">>";
+        fprintf(stream, "<<%s>>", ((oprogram*)this)->_value);
         break;
     case cmd_symbol:
-        stream << "'" << ((symbol*)this)->_value << "'";
+        fprintf(stream, "'%s'", ((oprogram*)this)->_value);
         break;
     case cmd_keyword:
     case cmd_branch:
-        stream << ((keyword*)this)->_value;
+        fprintf(stream, "%s", ((keyword*)this)->_value);
         break;
     default:
-        stream << "< unknown object representation >";
+        fprintf(stream, "< unknown object representation >");
         break;
     }
 }
@@ -749,7 +745,7 @@ public:
         if (st.size() == 1)
         {
             ((object*)st.back())->show();
-            cout<<endl;
+            printf("\n");
         }
         else
         {
@@ -757,9 +753,9 @@ public:
             for (int i = st.size()-1; i>=0; i--)
             {
                 if (show_sep)
-                    cout<<i+1<<separator;
+                    printf("%d%s", i+1, separator.c_str());
                 ((object*)st[i])->show();
-                cout<<endl;
+                printf("\n");
             }
         }
     }