Add C++11 Fl_Valuator::format API.

This is helpful for writing language wrapper, in
this particular case for PyFLTK.

FL/Fl_Color_Chooser.H

@@ -1,7 +1,7 @@
 //
 // Color chooser header file for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2019 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -30,6 +30,8 @@
 #include <FL/Fl_Choice.H>
 #include <FL/Fl_Value_Input.H>
 
+#include <string>
+
 #ifndef FL_DOXYGEN
 
 /** For internal use only */
@@ -60,6 +62,7 @@ public:
 class FL_EXPORT Flcc_Value_Input : public Fl_Value_Input {
 public:
   int format(char*) override;
+  std::string format_str() override;
   Flcc_Value_Input(int X, int Y, int W, int H) : Fl_Value_Input(X,Y,W,H) {}
 };
 

FL/Fl_Valuator.H

@@ -1,7 +1,7 @@
 //
 // Valuator header file for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2022 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -24,6 +24,8 @@
 #include "Fl_Widget.H"
 #endif
 
+#include <string>
+
 // shared type() values for classes that work in both directions:
 #define FL_VERTICAL             0 ///< The valuator can work vertically
 #define FL_HORIZONTAL           1 ///< The valuator can work horizontally
@@ -126,6 +128,7 @@ public:
   int value(double);
 
   virtual int format(char*);
+  virtual std::string format_str();
   double round(double); // round to nearest multiple of step
   double clamp(double); // keep in range
   double increment(double, int); // add n*step to value

src/Fl_Color_Chooser.cxx

@@ -1,7 +1,7 @@
 //
 // Color chooser for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2023 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -32,6 +32,7 @@
 // The "hue box" can be a circle or rectilinear.
 // You get a circle by defining this:
 #define CIRCLE 1
+
 // And the "hue box" can auto-update when the value changes
 // you get this by defining this:
 #define UPDATE_HUE_BOX 1
@@ -98,11 +99,21 @@ static const Fl_Menu_Item mode_menu[] = {
 };
 
 #ifndef FL_DOXYGEN
+
 int Flcc_Value_Input::format(char* buf) {
   Fl_Color_Chooser* c = (Fl_Color_Chooser*)parent();
   if (c->mode() == M_HEX) return snprintf(buf, 5,"0x%02X", int(value()));
   else return Fl_Valuator::format(buf);
 }
+
+// Note: although Flcc_Value_Input is marked private in the header files,
+// it nevertheless is publicly accessible, so implement this here just in case.
+std::string Flcc_Value_Input::format_str() {
+  char buffer[129];
+  int size = format(buffer);
+  return std::string(buffer, size);
+}
+
 #endif // !FL_DOXYGEN
 
 void Fl_Color_Chooser::set_valuators() {

src/Fl_Counter.cxx

@@ -1,7 +1,7 @@
 //
 // Counter widget for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2022 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -102,8 +102,8 @@ void Fl_Counter::draw() {
   draw_box(tbt, tx, y(), tw, h(), FL_BACKGROUND2_COLOR);
   fl_font(textfont(), textsize());
   fl_color(active_r() ? textcolor() : fl_inactive(textcolor()));
-  char str[128]; format(str);
-  fl_draw(str, tx, y(), tw, h(), FL_ALIGN_CENTER);
+  std::string str = format_str();
+  fl_draw(str.c_str(), tx, y(), tw, h(), FL_ALIGN_CENTER);
   if (Fl::focus() == this) draw_focus(tbt, tx, y(), tw, h());
   if (!(damage()&FL_DAMAGE_ALL)) return; // only need to redraw text
 

src/Fl_Valuator.cxx

@@ -1,7 +1,7 @@
 //
 // Valuator widget for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2016 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -175,7 +175,7 @@ int Fl_Valuator::format(char* buffer) {
   int i, c = 0;
   char temp[32];
   // output a number with many digits after the decimal point. This
-  // seems to be needed to get high precission
+  // seems to be needed to get high precision
   snprintf(temp, sizeof(temp), "%.12f", A/B);
   // strip all trailing 0's
   for (i=(int) strlen(temp)-1; i>0; i--) {
@@ -190,3 +190,16 @@ int Fl_Valuator::format(char* buffer) {
   // MRS: THIS IS A HACK - RECOMMEND ADDING BUFFER SIZE ARGUMENT
   return snprintf(buffer, 128, "%.*f", c, v);
 }
+
+/**
+  \brief C++11 API for Fl_Valuator::format(char* buffer).
+  Users can override either version to change the format of the text output
+  in the valuator.
+  \return the formatted text of the current value
+  \see Fl_Valuator::format(char* buffer)
+ */
+std::string Fl_Valuator::format_str() {
+  char buffer[129];
+  int size = format(buffer);
+  return std::string(buffer, size);
+}

src/Fl_Value_Input.cxx

@@ -1,7 +1,7 @@
 //
 // Value input widget for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2010 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -51,9 +51,8 @@ void Fl_Value_Input::resize(int X, int Y, int W, int H) {
 }
 
 void Fl_Value_Input::value_damage() {
-  char buf[128];
-  format(buf);
-  input.value(buf);
+  std::string buf = format_str();
+  input.value(buf.c_str());
   input.mark(input.insert_position()); // turn off selection highlight
 }
 

src/Fl_Value_Output.cxx

@@ -1,7 +1,7 @@
 //
 // Value output widget for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2010 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -34,11 +34,10 @@ void Fl_Value_Output::draw() {
     fl_color(color());
     fl_rectf(X, Y, W, H);
   }
-  char buf[128];
-  format(buf);
+  std::string buf = format_str();
   fl_color(active_r() ? textcolor() : fl_inactive(textcolor()));
   fl_font(textfont(), textsize());
-  fl_draw(buf,X,Y,W,H,FL_ALIGN_LEFT);
+  fl_draw(buf.c_str(),X,Y,W,H,FL_ALIGN_LEFT);
 }
 
 int Fl_Value_Output::handle(int event) {

src/Fl_Value_Slider.cxx

@@ -1,7 +1,7 @@
 //
 // Value Slider widget for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2022 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -53,11 +53,10 @@ void Fl_Value_Slider::draw() {
                   sww-Fl::box_dw(box()),
                   shh-Fl::box_dh(box()));
   draw_box(box(),bxx,byy,bww,bhh,color());
-  char buf[128];
-  format(buf);
+  std::string buf = format_str();
   fl_font(textfont(), textsize());
   fl_color(active_r() ? textcolor() : fl_inactive(textcolor()));
-  fl_draw(buf, bxx, byy, bww, bhh, FL_ALIGN_CLIP);
+  fl_draw(buf.c_str(), bxx, byy, bww, bhh, FL_ALIGN_CLIP);
 }
 
 int Fl_Value_Slider::handle(int event) {

test/adjuster.cxx

@@ -1,7 +1,7 @@
 //
 // Adjuster test program for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2010 by Bill Spitzak and others.
+// Copyright 1998-2026 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -23,29 +23,30 @@
 void adjcb(Fl_Widget *o, void *v) {
   Fl_Adjuster *a = (Fl_Adjuster*)o;
   Fl_Box *b = (Fl_Box *)v;
-  a->format((char *)(b->label()));
+  std::string new_label = a->format_str();
+  b->copy_label(new_label.c_str());
   b->redraw();
 }
 
 int main(int argc, char ** argv) {
-   Fl_Double_Window window(320,100,argv[0]);
+  Fl_Double_Window window(320, 100, argv[0]);
 
-   char buf1[100];
-   Fl_Box b1(FL_DOWN_BOX,20,30,80,25,buf1);
-   b1.color(FL_WHITE);
-   Fl_Adjuster a1(20+80,30,3*25,25);
-   a1.callback(adjcb,&b1);
-   adjcb(&a1,&b1);
+  Fl_Box b1(20, 30, 80, 25);
+  b1.box(FL_DOWN_BOX);
+  b1.color(FL_WHITE);
+  Fl_Adjuster a1(20+80, 30, 3*25, 25);
+  a1.callback(adjcb, &b1);
+  adjcb(&a1, &b1);
 
-   char buf2[100];
-   Fl_Box b2(FL_DOWN_BOX,20+80+4*25,30,80,25,buf2);
-   b2.color(FL_WHITE);
-   Fl_Adjuster a2(b2.x()+b2.w(),10,25,3*25);
-   a2.callback(adjcb,&b2);
-   adjcb(&a2,&b2);
+  Fl_Box b2(20+80+4*25, 30, 80, 25);
+  b2.box(FL_DOWN_BOX);
+  b2.color(FL_WHITE);
+  Fl_Adjuster a2(b2.x()+b2.w(), 10, 25, 3*25);
+  a2.callback(adjcb, &b2);
+  adjcb(&a2, &b2);
 
-   window.resizable(window);
-   window.end();
-   window.show(argc, argv);
-   return Fl::run();
+  window.resizable(window);
+  window.end();
+  window.show(argc, argv);
+  return Fl::run();
 }