Support changing color mode at runtime

README.md

@@ -1626,10 +1626,53 @@ std::cerr << toml::format_error("[error] value should be positive",
                                 hints, /*colorize = */ true) << std::endl;
 ```
 
-Note: It colorize `[error]` in red. That means that it detects `[error]` prefix
+Note: It colorizes `[error]` in red. That means that it detects `[error]` prefix
 at the front of the error message. If there is no `[error]` prefix,
 `format_error` adds it to the error message.
 
+Compared to the `TOML11_COLORIZE_ERROR_MESSAGE` macro that enables colorization
+statically, toml11 provides `toml::color::enable` & `toml::color::disable`
+functions to dynamically change the color mode. This feature overwrites
+`TOML11_COLORIZE_ERROR_MESSAGE` and the `colorize` argument of
+`toml::format_error` when you call `enable`.
+
+Note: If either `TOML11_COLORIZE_ERROR_MESSAGE` is defined or the `colorize`
+argument is used, it takes precedence, meaning that `disable` won't work.
+Accordingly, we highly recommend using only one of them.
+
+```cpp
+toml::color::enable();  // enable colorization
+toml::color::disable(); // disable colorization
+```
+
+If you use user-defined error message, you can manage the setting as follows:
+
+```cpp
+toml::color::enable();
+std::cerr << toml::format_error("[error] value should be positive",
+                                data.at("num"), "positive number required",
+                                hints) << std::endl; // colorized
+
+toml::color::disable();
+std::cerr << toml::format_error("[error] value should be positive",
+                                data.at("num"), "positive number required",
+                                hints) << std::endl; // NOT colorized
+```
+
+Or you may use toml11 in your application like:
+
+```cpp
+std::vector<std::string> args(argv + 1, argv + argc);
+auto result = std::find(args.begin(), args.end(), "--color");
+if (result != args.end()) {
+    toml::color::enable();
+} else {
+    toml::color::disable();
+}
+
+// use toml11 ...
+```
+
 ## Opting out of the default `[error]` prefix
 
 toml11 prints error messages with the `[error]` prefix by default.

toml/color.hpp

@@ -17,11 +17,36 @@ namespace color_ansi
 {
 namespace detail
 {
+
 inline int colorize_index()
 {
     static const int index = std::ios_base::xalloc();
     return index;
 }
+
+// Control color mode globally
+class color_mode {
+public:
+    inline void enable() {
+        should_color_ = true;
+    }
+    inline void disable() {
+        should_color_ = false;
+    }
+
+    inline bool should_color() const {
+        return should_color_;
+    }
+
+    static color_mode& status() {
+        static color_mode status_;
+        return status_;
+    }
+
+private:
+    bool should_color_ = false;
+};
+
 } // detail
 
 inline std::ostream& colorize(std::ostream& os)
@@ -55,6 +80,18 @@ inline std::ostream& cyan   (std::ostream& os)
 {if(os.iword(detail::colorize_index()) == 1) {os << "\033[36m";} return os;}
 inline std::ostream& white  (std::ostream& os)
 {if(os.iword(detail::colorize_index()) == 1) {os << "\033[37m";} return os;}
+
+inline void enable() {
+    return detail::color_mode::status().enable();
+}
+inline void disable() {
+    return detail::color_mode::status().disable();
+}
+
+inline bool should_color() {
+    return detail::color_mode::status().should_color();
+}
+
 } // color_ansi
 
 // ANSI escape sequence is the only and default colorization method currently

toml/source_location.hpp

@@ -125,7 +125,7 @@ inline std::string format_underline(const std::string& message,
 
     std::ostringstream retval;
 
-    if(colorize)
+    if(color::should_color() || colorize)
     {
         retval << color::colorize; // turn on ANSI color
     }