custom printfArgFormatter template param

fmt/format.cc

@@ -686,8 +686,8 @@ FMT_FUNC Arg fmt::internal::FormatterBase::do_get_arg(
   return arg;
 }
 
-template <typename Char>
-void fmt::internal::PrintfFormatter<Char>::parse_flags(
+template <typename Char, typename PAF>
+void fmt::internal::PrintfFormatter<Char, PAF>::parse_flags(
     FormatSpec &spec, const Char *&s) {
   for (;;) {
     switch (*s++) {
@@ -713,8 +713,8 @@ void fmt::internal::PrintfFormatter<Char>::parse_flags(
   }
 }
 
-template <typename Char>
-Arg fmt::internal::PrintfFormatter<Char>::get_arg(
+template <typename Char, typename PAF>
+Arg fmt::internal::PrintfFormatter<Char, PAF>::get_arg(
     const Char *s, unsigned arg_index) {
   (void)s;
   const char *error = 0;
@@ -725,8 +725,8 @@ Arg fmt::internal::PrintfFormatter<Char>::get_arg(
   return arg;
 }
 
-template <typename Char>
-unsigned fmt::internal::PrintfFormatter<Char>::parse_header(
+template <typename Char, typename PAF>
+unsigned fmt::internal::PrintfFormatter<Char, PAF>::parse_header(
   const Char *&s, FormatSpec &spec) {
   unsigned arg_index = UINT_MAX;
   Char c = *s;
@@ -759,8 +759,8 @@ unsigned fmt::internal::PrintfFormatter<Char>::parse_header(
   return arg_index;
 }
 
-template <typename Char>
-void fmt::internal::PrintfFormatter<Char>::format(
+template <typename Char, typename PAF >
+  void fmt::internal::PrintfFormatter<Char,PAF>::format(
     BasicWriter<Char> &writer, BasicCStringRef<Char> format_str) {
   const Char *start = format_str.c_str();
   const Char *s = start;
@@ -853,11 +853,12 @@ void fmt::internal::PrintfFormatter<Char>::format(
     start = s;
 
     // Format argument.
-    internal::PrintfArgFormatter<Char>(writer, spec).visit(arg);
+    PAF(writer, spec).visit(arg);
   }
   write(writer, start, s);
 }
 
+
 FMT_FUNC void fmt::report_system_error(
     int error_code, fmt::StringRef message) FMT_NOEXCEPT {
   // 'fmt::' is for bcc32.

fmt/format.h

@@ -378,6 +378,7 @@ class BasicWriter;
 typedef BasicWriter<char> Writer;
 typedef BasicWriter<wchar_t> WWriter;
 
+// Define default ArgFormatter and BasicFormatter.
 template <typename Char>
 class ArgFormatter;
 
@@ -1939,7 +1940,7 @@ class FormatterBase {
 };
 
 // A printf formatter.
-template <typename Char>
+ template <typename Char, typename PAF = fmt::internal::PrintfArgFormatter<Char> >
 class PrintfFormatter : private FormatterBase {
  private:
   void parse_flags(FormatSpec &spec, const Char *&s);
@@ -3187,9 +3188,9 @@ FMT_API void print(std::FILE *f, CStringRef format_str, ArgList args);
  */
 FMT_API void print(CStringRef format_str, ArgList args);
 
-template <typename Char>
+ template <typename Char>
 void printf(BasicWriter<Char> &w, BasicCStringRef<Char> format, ArgList args) {
-  internal::PrintfFormatter<Char>(args).format(w, format);
+   internal::PrintfFormatter<Char>(args).format(w, format);
 }
 
 /**
@@ -3815,8 +3816,10 @@ struct UdlArg {
   }
 };
 
+
 } // namespace internal
 
+
 inline namespace literals {
 
 /**
@@ -3850,6 +3853,7 @@ inline internal::UdlArg<wchar_t>
 operator"" _a(const wchar_t *s, std::size_t) { return {s}; }
 
 } // inline namespace literals
+
 } // namespace fmt
 #endif // FMT_USE_USER_DEFINED_LITERALS
 

test/CMakeLists.txt

@@ -80,6 +80,7 @@ add_fmt_test(printf-test)
 add_fmt_test(string-test)
 add_fmt_test(util-test mock-allocator.h)
 add_fmt_test(macro-test)
+add_fmt_test(custom-formatter-test)
 
 # Enable stricter options for one test to make sure that the header is free of
 # warnings.

test/custom-formatter-test.cc

@@ -0,0 +1,41 @@
+#include "fmt/format.h"
+#include <iostream>
+
+// A custom argument formatter that doesn't print `-` for floating-point values
+// rounded to 0.
+class CustomArgFormatter :
+  public fmt::BasicArgFormatter<CustomArgFormatter, char>  {
+  public:
+  CustomArgFormatter(fmt::BasicFormatter<char, CustomArgFormatter> &f,
+                     fmt::FormatSpec &s, const char *fmt)
+    : fmt::BasicArgFormatter<CustomArgFormatter, char>(f, s, fmt) {}
+
+  void visit_double(double value) {
+    if (round(value * pow(10, spec().precision())) == 0)
+      value = 0;
+    fmt::BasicArgFormatter<CustomArgFormatter, char>::visit_double(value);
+  }
+};
+
+std::string custom_format(const char *format_str, fmt::ArgList args) {
+  fmt::MemoryWriter writer;
+  // Pass custom argument formatter as a template arg to BasicFormatter.
+  fmt::BasicFormatter<char, CustomArgFormatter> formatter(args, writer);
+  formatter.format(format_str);
+  return writer.str();
+}
+FMT_VARIADIC(std::string, custom_format, const char *)
+
+std::string printfer(const char* fstr, fmt::ArgList args){
+  fmt::MemoryWriter writer;
+  fmt::internal::PrintfFormatter<char> pfer(args);
+  pfer.format(writer,fstr);
+  return writer.str();
+}
+
+FMT_VARIADIC(std::string, printfer, const char*);
+
+int main() {
+  std::cout << custom_format("custom: {:.2f}", -0.000001) << std::endl;
+  std::cout << printfer("printf: %.2f", -0.0001) << std::endl;
+}