Allow formatting C strings as pointers (#223)

format.cc

@@ -409,6 +409,12 @@ class BasicArgFormatter : public ArgVisitor<Impl, void> {
 
   FMT_DISALLOW_COPY_AND_ASSIGN(BasicArgFormatter);
 
+  void write_pointer(const void *p) {
+    spec_.flags_ = HASH_FLAG;
+    spec_.type_ = 'x';
+    writer_.write_int(reinterpret_cast<uintptr_t>(p), spec_);
+  }
+
  protected:
   BasicWriter<Char> &writer() { return writer_; }
   const FormatSpec &spec() const { return spec_; }
@@ -462,6 +468,15 @@ class BasicArgFormatter : public ArgVisitor<Impl, void> {
     *out = internal::CharTraits<Char>::cast(value);
   }
 
+  void visit_cstring(const char *value) {
+    if (spec_.type_ == 'p') {
+      write_pointer(value);
+      return;
+    }
+    Arg::StringValue<char> str = {value, 0};
+    writer_.write_str(str, spec_);
+  }
+
   void visit_string(Arg::StringValue<char> value) {
     writer_.write_str(value, spec_);
   }
@@ -475,9 +490,7 @@ class BasicArgFormatter : public ArgVisitor<Impl, void> {
   void visit_pointer(const void *value) {
     if (spec_.type_ && spec_.type_ != 'p')
       report_unknown_type(spec_.type_, "pointer");
-    spec_.flags_ = HASH_FLAG;
-    spec_.type_ = 'x';
-    writer_.write_int(reinterpret_cast<uintptr_t>(value), spec_);
+    write_pointer(value);
   }
 };
 

format.h

@@ -1186,6 +1186,9 @@ class ArgVisitor {
     return FMT_DISPATCH(visit_unhandled_arg());
   }
 
+  Result visit_cstring(const char *) {
+    return FMT_DISPATCH(visit_unhandled_arg());
+  }
   Result visit_string(Arg::StringValue<char>) {
     return FMT_DISPATCH(visit_unhandled_arg());
   }
@@ -1220,11 +1223,8 @@ class ArgVisitor {
       return FMT_DISPATCH(visit_double(arg.double_value));
     case Arg::LONG_DOUBLE:
       return FMT_DISPATCH(visit_long_double(arg.long_double_value));
-    case Arg::CSTRING: {
-      Arg::StringValue<char> str = arg.string;
-      str.size = 0;
-      return FMT_DISPATCH(visit_string(str));
-    }
+    case Arg::CSTRING:
+      return FMT_DISPATCH(visit_cstring(arg.string.value));
     case Arg::STRING:
       return FMT_DISPATCH(visit_string(arg.string));
     case Arg::WSTRING:

test/format-test.cc

@@ -1336,7 +1336,7 @@ TEST(FormatterTest, FormatWChar) {
 }
 
 TEST(FormatterTest, FormatCString) {
-  check_unknown_types("test", "s", "string");
+  check_unknown_types("test", "sp", "string");
   EXPECT_EQ("test", format("{0}", "test"));
   EXPECT_EQ("test", format("{0:s}", "test"));
   char nonconst[] = "nonconst";

test/printf-test.cc

@@ -425,6 +425,8 @@ TEST(PrintfTest, Pointer) {
   int n;
   void *p = &n;
   EXPECT_PRINTF(fmt::format("{}", p), "%p", p);
+  const char *s = "test";
+  EXPECT_PRINTF(fmt::format("{:p}", s), "%p", s);
 }
 
 TEST(PrintfTest, Custom) {

test/util-test.cc

@@ -593,6 +593,7 @@ struct TestVisitor : fmt::internal::ArgVisitor<TestVisitor, Result> {
   Result visit_double(double value) { return value; }
   Result visit_long_double(long double value) { return value; }
   Result visit_char(int value) { return static_cast<char>(value); }
+  Result visit_cstring(const char *s) { return s; }
   Result visit_string(Arg::StringValue<char> s) { return s.value; }
   Result visit_wstring(Arg::StringValue<wchar_t> s) { return s.value; }
   Result visit_pointer(const void *p) { return p; }