Fl_Input

API reference for the Fl_Input class in FLTK

Fl_Input

The Fl_Input widget displays a single line of text and allows the user to edit it. It provides comprehensive text editing capabilities with support for UTF-8, clipboard operations, and keyboard navigation.

Header File

#include <FL/Fl_Input.H>

Class Overview

Fl_Input is the standard single-line text input widget in FLTK. It features:

• Single-line text editing with full UTF-8 support
• Mouse and keyboard-based text selection
• Clipboard integration (cut, copy, paste)
• Undo/redo functionality
• Customizable appearance and behavior
• Support for input validation and filtering

Inheritance

Fl_Widget
  └── Fl_Input_
        └── Fl_Input

Inherits from: Fl_Input_ (which inherits from Fl_Widget)

Constructor

Fl_Input(int X, int Y, int W, int H, const char *L = 0)

Creates a new single-line input field.

X · int

The X coordinate of the input field relative to the enclosing window

Y · int

The Y coordinate of the input field relative to the enclosing window

W · int

Width of the input field in pixels

H · int

Height of the input field in pixels

L · const char* · default: "nullptr"

Label text displayed next to the input field

Public Methods

handle()

int handle(int event) override

Handles events for the input field including keyboard input, mouse clicks, and clipboard operations.

event · int

The FLTK event type (e.g., FL_KEYBOARD, FL_PUSH, FL_PASTE)

Returns: int - 1 if handled, 0 otherwise

Protected Methods

draw()

void draw() override

Draws the input field with its current text and cursor. Called automatically by FLTK.

Inherited Methods from Fl_Input_

The Fl_Input class inherits extensive functionality from Fl_Input_:

Text Management

• value() / value(const char*) - Get or set the text content
• size() - Get the length of text in bytes
• maximum_size() / maximum_size(int) - Get or set maximum text length
• insert(const char*) - Insert text at cursor position
• replace(int, int, const char*) - Replace text in a range
• cut() - Cut selected text to clipboard
• copy() - Copy selected text to clipboard
• undo() - Undo last edit operation

Selection and Cursor

• position() / position(int) - Get or set cursor position
• mark() / mark(int) - Get or set selection mark
• position(int, int) - Set cursor position and selection mark
• insert_position() - Get current cursor position

Appearance

• textcolor() / textcolor(Fl_Color) - Get or set text color
• textfont() / textfont(Fl_Font) - Get or set text font
• textsize() / textsize(Fl_Fontsize) - Get or set text size
• cursor_color() / cursor_color(Fl_Color) - Get or set cursor color

Behavior

• readonly() / readonly(int) - Get or set read-only mode
• wrap() / wrap(int) - Get or set text wrapping (multiline variants)
• tab_nav() / tab_nav(int) - Control tab key navigation

Mouse and Keyboard Bindings

Mouse Operations

Mouse Action	Behavior
Button 1 Click	Moves cursor to click point
Button 1 Drag	Selects characters
Double Click	Selects word
Triple Click	Selects all text
Shift+Click	Extends selection
Button 2	Pastes selection buffer at click point
Button 3	Acts like button 1

Keyboard Shortcuts

Windows/Linux → Mac → Function

Windows/Linux	Mac	Function
Ctrl+A	Cmd+A	Select all text
Ctrl+C	Cmd+C	Copy to clipboard
Ctrl+V	Cmd+V	Paste from clipboard
Ctrl+X	Cmd+X	Cut to clipboard
Ctrl+Z	Cmd+Z	Undo
Shift+Ctrl+Z	Shift+Cmd+Z	Redo
Backspace	Backspace	Delete character left
Delete	Delete	Delete character right
Shift+Delete	Shift+Delete	Cut to clipboard
Shift+Insert	-	Paste from clipboard
Arrow Keys	Arrow Keys	Cursor movement (combine with Shift to select)
Home	Cmd+Left	Move to start of line
End	Cmd+Right	Move to end of line
Ctrl+Left	Alt+Left	Move word left
Ctrl+Right	Alt+Right	Move word right
Ctrl+Backspace	Alt+Backspace	Delete word left
Ctrl+Delete	Alt+Delete	Delete word right

Usage Example

From test/input.cxx:

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Input.H>
#include <FL/Fl_Float_Input.H>
#include <FL/Fl_Int_Input.H>
#include <FL/Fl_Secret_Input.H>
#include <FL/Fl_Button.H>
#include <stdio.h>

void input_cb(Fl_Widget *ob) {
  printf("Callback for %s: '%s'\n", 
         ob->label(), 
         ((Fl_Input*)ob)->value());
}

int main(int argc, char **argv) {
  Fl_Window *window = new Fl_Window(400, 300);
  
  int y = 10;
  
  // Normal text input
  Fl_Input *normal = new Fl_Input(70, y, 300, 30, "Normal:");
  normal->tooltip("Normal input field");
  normal->callback(input_cb);
  normal->when(FL_WHEN_CHANGED);
  y += 35;
  
  // Float input (validates floating-point numbers)
  Fl_Float_Input *floatinput = new Fl_Float_Input(70, y, 300, 30, "Float:");
  floatinput->tooltip("Floating-point number input (F1)");
  floatinput->shortcut(FL_F+1);
  y += 35;
  
  // Integer input (validates integers)
  Fl_Int_Input *intinput = new Fl_Int_Input(70, y, 300, 30, "Int:");
  intinput->tooltip("Integer number input (F2)");
  intinput->shortcut(FL_F+2);
  y += 35;
  
  // Secret input (password field)
  Fl_Secret_Input *secret = new Fl_Secret_Input(70, y, 300, 30, "&Secret:");
  secret->tooltip("Password input field (Alt-S)");
  y += 35;
  
  window->end();
  window->show(argc, argv);
  return Fl::run();
}

Advanced Example: Input Validation

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Input.H>
#include <ctype.h>

void validate_cb(Fl_Widget *w, void *) {
  Fl_Input *input = (Fl_Input*)w;
  const char *text = input->value();
  
  // Example: only allow alphanumeric characters
  for (int i = 0; text[i]; i++) {
    if (!isalnum(text[i]) && text[i] != ' ') {
      input->color(FL_RED);
      input->redraw();
      return;
    }
  }
  
  input->color(FL_WHITE);
  input->redraw();
}

int main(int argc, char **argv) {
  Fl_Window *window = new Fl_Window(350, 100);
  
  Fl_Input *input = new Fl_Input(10, 30, 330, 30, "Alphanumeric only:");
  input->align(FL_ALIGN_TOP_LEFT);
  input->callback(validate_cb);
  input->when(FL_WHEN_CHANGED);
  
  window->end();
  window->show(argc, argv);
  return Fl::run();
}

Input Variants

FLTK provides several specialized input classes:

• Fl_Float_Input - Validates floating-point numbers
• Fl_Int_Input - Validates integer numbers
• Fl_Secret_Input - Password field (displays bullets)
• Fl_Multiline_Input - Multi-line text input
• Fl_File_Input - File path input with browse button

See Also

• Fl_Output - Read-only text display
• Fl_Text_Editor - Advanced multi-line text editor
• Fl_Text_Display - Multi-line text display
• Fl_Input_ - Base class for input widgets