PR#394: don't always append the ".0" if the double value rounds to zero because some custom formats *will* include it (e.g. %.2f).

Also try to accomodate formats to explicitly exclude the decimal (e.g. %.0f).

json_object.c

@@ -15,6 +15,7 @@
 #include "strerror_override.h"
 
 #include <assert.h>
+#include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stddef.h>
@@ -787,7 +788,6 @@ static int json_object_double_to_json_string_format(struct json_object* jso,
 {
 	char buf[128], *p, *q;
 	int size;
-	double dummy; /* needed for modf() */
 	/* Although JSON RFC does not support
 	NaN or Infinity as numeric values
 	ECMA 262 section 9.8.1 defines
@@ -807,24 +807,20 @@ static int json_object_double_to_json_string_format(struct json_object* jso,
 	{
 		const char *std_format = "%.17g";
 
+		if (!format)
+		{
 #if defined(HAVE___THREAD)
 			if (tls_serialization_float_format)
-			std_format = tls_serialization_float_format;
+				format = tls_serialization_float_format;
 			else
 #endif
 			if (global_serialization_float_format)
-			std_format = global_serialization_float_format;
+				format = global_serialization_float_format;
-		if (!format)
+			else
 				format = std_format;
+		}
 		size = snprintf(buf, sizeof(buf), format, jso->o.c_double);
-		if (modf(jso->o.c_double, &dummy) == 0  && size >= 0 && size < (int)sizeof(buf) - 2)
+
-		{
-			// Ensure it looks like a float, even if snprintf didn't.
-			strcat(buf, ".0");
-			size += 2;
-		}
-	}
-	// although unlikely, snprintf can fail
 		if (size < 0)
 			return -1;
 
@@ -833,6 +829,22 @@ static int json_object_double_to_json_string_format(struct json_object* jso,
 			*p = '.';
 		else
 			p = strchr(buf, '.');
+
+		int format_drops_decimals = 0;
+		if (format == std_format || strstr(format, ".0f") == NULL)
+			format_drops_decimals = 1;
+
+		if (size < (int)sizeof(buf) - 2 &&
+		    isdigit((int)buf[0]) && /* Looks like *some* kind of number */
+			!p && /* Has no decimal point */
+		    strchr(buf, 'e') == NULL && /* Not scientific notation */
+			format_drops_decimals)
+		{
+			// Ensure it looks like a float, even if snprintf didn't,
+			//  unless a custom format is set to omit the decimal.
+			strcat(buf, ".0");
+			size += 2;
+		}
 		if (p && (flags & JSON_C_TO_STRING_NOZERO))
 		{
 			/* last useful digit, always keep 1 zero */
@@ -844,6 +856,10 @@ static int json_object_double_to_json_string_format(struct json_object* jso,
 			*(++p) = 0;
 			size = p-buf;
 		}
+	}
+	// although unlikely, snprintf can fail
+	if (size < 0)
+		return -1;
 
 	if (size >= (int)sizeof(buf))
 		// The standard formats are guaranteed not to overrun the buffer,

tests/test_double_serializer.c

@@ -54,4 +54,24 @@ int main()
 	printf("obj.to_string(back to default format)=%s\n", json_object_to_json_string(obj));
 
 	json_object_put(obj);
+
+	obj = json_object_new_double(12.0);
+	printf("obj(12.0).to_string(default format)=%s\n", json_object_to_json_string(obj));
+	if (json_c_set_serialization_double_format("%.0f", JSON_C_OPTION_GLOBAL) < 0)
+		printf("ERROR: json_c_set_serialization_double_format() failed");
+	printf("obj(12.0).to_string(%%.0f)=%s\n", json_object_to_json_string(obj));
+
+	if (json_c_set_serialization_double_format("%.0g", JSON_C_OPTION_GLOBAL) < 0)
+		printf("ERROR: json_c_set_serialization_double_format() failed");
+	printf("obj(12.0).to_string(%%.0g)=%s\n", json_object_to_json_string(obj));
+
+	if (json_c_set_serialization_double_format("%.2g", JSON_C_OPTION_GLOBAL) < 0)
+		printf("ERROR: json_c_set_serialization_double_format() failed");
+	printf("obj(12.0).to_string(%%.1g)=%s\n", json_object_to_json_string(obj));
+
+	// Reset to default to free memory
+	if (json_c_set_serialization_double_format(NULL, JSON_C_OPTION_GLOBAL) < 0)
+		printf("ERROR: json_c_set_serialization_double_format() failed");
+
+	json_object_put(obj);
 }

tests/test_double_serializer.expected

@@ -12,3 +12,7 @@ obj.to_string(with thread format)=T0.52X
 obj.to_string(long thread format)=Ttttttttttttt0.52xxxxxxxxxxxxxxxxxxX
 obj.to_string(back to global format)=x0.524y
 obj.to_string(back to default format)=0.52381
+obj(12.0).to_string(default format)=12.0
+obj(12.0).to_string(%.0f)=12
+obj(12.0).to_string(%.0g)=1e+01
+obj(12.0).to_string(%.1g)=12.0