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

@@ -237,7 +237,7 @@ typedef __int64          intmax_t;
 # define FMT_BUILTIN_CLZLL(n) __builtin_clzll(n)
 #endif
 
-// Some compilers masquerade as both MSVC and GCC-likes or 
+// Some compilers masquerade as both MSVC and GCC-likes or
 // otherwise support __builtin_clz and __builtin_clzll, so
 // only define FMT_BUILTIN_CLZ using the MSVC intrinsics
 // if the clz and clzll builtins are not available.
@@ -253,7 +253,7 @@ inline uint32_t clz(uint32_t x) {
 
   assert(x != 0);
   // Static analysis complains about using uninitialized data
-  // "r", but the only way that can happen is if "x" is 0, 
+  // "r", but the only way that can happen is if "x" is 0,
   // which the callers guarantee to not happen.
 # pragma warning(suppress: 6102)
   return 31 - r;
@@ -279,7 +279,7 @@ inline uint32_t clzll(uint64_t x) {
 
   assert(x != 0);
   // Static analysis complains about using uninitialized data
-  // "r", but the only way that can happen is if "x" is 0, 
+  // "r", but the only way that can happen is if "x" is 0,
   // which the callers guarantee to not happen.
 # pragma warning(suppress: 6102)
   return 63 - r;
@@ -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;
 
@@ -1296,7 +1297,7 @@ public:
   MakeArg() {
     type = Arg::NONE;
   }
-  
+
   template <typename T>
   MakeArg(const T &value)
   : Arg(MakeValue<Formatter>(value)) {
@@ -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);
@@ -2091,7 +2092,7 @@ struct ArgArray;
 template <unsigned N>
 struct ArgArray<N, true/*IsPacked*/> {
   typedef Value Type[N > 0 ? N : 1];
-  
+
   template <typename Formatter, typename T>
   static Value make(const T &value) {
 #ifdef __clang__
@@ -2287,7 +2288,7 @@ class SystemError : public internal::RuntimeError {
   Formats an error returned by an operating system or a language runtime,
   for example a file opening error, and writes it to *out* in the following
   form:
-   
+
   .. parsed-literal::
      *<message>*: *<system-message>*
 
@@ -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.
@@ -129,7 +130,7 @@ if (FMT_PEDANTIC)
     "${CMAKE_CURRENT_BINARY_DIR}/compile-test"
     --build-generator ${CMAKE_GENERATOR}
     --build-makeprogram ${CMAKE_MAKE_PROGRAM}
-    --build-options 
+    --build-options
     "-DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}"
     "-DCPP11_FLAG=${CPP11_FLAG}"
     "-DSUPPORTS_USER_DEFINED_LITERALS=${SUPPORTS_USER_DEFINED_LITERALS}")

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;
+}