Number decimal point

README.md

@@ -200,6 +200,8 @@ typedef struct cJSON
     /* writing to valueint is DEPRECATED, use cJSON_SetNumberValue instead */
     int valueint;
     double valuedouble;
+    /* Decimal places used when printing non-integral values; 0 uses default formatting. */
+    int decimal_places;
     char *string;
 } cJSON;
 ```
@@ -279,6 +281,44 @@ To iterate over an object, you can use the `cJSON_ArrayForEach` macro the same w
 
 cJSON also provides convenient helper functions for quickly creating a new item and adding it to an object, like `cJSON_AddNullToObject`. They return a pointer to the new item or `NULL` if they failed.
 
+`cJSON_AddNumberWithPrecisionToObject` specifies the number of digits after the decimal point when printing a non-integral value. Non-integral values are padded or rounded as needed. Integral values are printed without a decimal point or trailing zeroes. `decimal_places` must be between 1 and 14. For example, the following rounds the representation of pi to six decimal places while leaving an integral value unchanged:
+
+```c
+/* Returns a heap-allocated string that must be released with cJSON_free. */
+char *create_numbers_with_precision(void)
+{
+    char *string = NULL;
+    cJSON *object = cJSON_CreateObject();
+
+    if (object == NULL)
+    {
+        return NULL;
+    }
+
+    if (cJSON_AddNumberWithPrecisionToObject(object, "pi", 3.141592653589793, 6) == NULL)
+    {
+        goto end;
+    }
+
+    if (cJSON_AddNumberWithPrecisionToObject(object, "integer", 3.0, 5) == NULL)
+    {
+        goto end;
+    }
+
+    string = cJSON_PrintUnformatted(object);
+
+end:
+    cJSON_Delete(object);
+    return string;
+}
+```
+
+The generated JSON is:
+
+```json
+{"pi":3.141593,"integer":3}
+```
+
 ### Parsing JSON
 
 Given some JSON in a zero terminated string, you can parse it with `cJSON_Parse`.

cJSON.c

@@ -619,14 +619,20 @@ static cJSON_bool print_number(const cJSON * const item, printbuffer * const out
     }
     else
     {
-        /* Try 15 decimal places of precision to avoid nonsignificant nonzero digits */
-        length = sprintf((char*)number_buffer, "%1.15g", d);
-
-        /* Check whether the original double can be recovered */
-        if ((sscanf((char*)number_buffer, "%lg", &test) != 1) || !compare_double((double)test, d))
-        {
-            /* If not, print with 17 decimal places of precision */
-            length = sprintf((char*)number_buffer, "%1.17g", d);
+        /* Apply decimal-place formatting only when the value has a fractional part. */
+        if (item->decimal_places && (ceil(d) != d)) {
+            /* Then convert it to string */
+            length = sprintf((char*) number_buffer, "%.*f", item->decimal_places, d);
+        } else {
+            /* Try 15 decimal places of precision to avoid nonsignificant nonzero digits */
+            length = sprintf((char*)number_buffer, "%1.15g", d);
+
+            /* Check whether the original double can be recovered */
+            if ((sscanf((char*)number_buffer, "%lg", &test) != 1) || !compare_double((double)test, d))
+            {
+                /* If not, print with 17 decimal places of precision */
+                length = sprintf((char*)number_buffer, "%1.17g", d);
+            }
         }
     }
 
@@ -2207,6 +2213,27 @@ CJSON_PUBLIC(cJSON*) cJSON_AddNumberToObject(cJSON * const object, const char *
     return NULL;
 }
 
+CJSON_PUBLIC(cJSON*) cJSON_AddNumberWithPrecisionToObject(cJSON * const object, const char * const name, const double n, int decimal_places)
+{
+    cJSON *number_item;
+
+    if (decimal_places <= 0 || decimal_places > 14)
+    {
+        return NULL;
+    }
+
+    number_item = cJSON_CreateNumber(n);
+
+    if (add_item_to_object(object, name, number_item, &global_hooks, false))
+    {
+        number_item->decimal_places = decimal_places;
+        return number_item;
+    }
+
+    cJSON_Delete(number_item);
+    return NULL;
+}
+
 CJSON_PUBLIC(cJSON*) cJSON_AddStringToObject(cJSON * const object, const char * const name, const char * const string)
 {
     cJSON *string_item = cJSON_CreateString(string);

cJSON.h

@@ -117,6 +117,8 @@ typedef struct cJSON
     int valueint;
     /* The item's number, if type==cJSON_Number */
     double valuedouble;
+    /* Decimal places used when printing non-integral values; 0 uses default formatting. */
+    int decimal_places;
 
     /* The item's name string, if this item is the child of, or is in the list of subitems of an object. */
     char *string;
@@ -272,6 +274,7 @@ CJSON_PUBLIC(cJSON*) cJSON_AddTrueToObject(cJSON * const object, const char * co
 CJSON_PUBLIC(cJSON*) cJSON_AddFalseToObject(cJSON * const object, const char * const name);
 CJSON_PUBLIC(cJSON*) cJSON_AddBoolToObject(cJSON * const object, const char * const name, const cJSON_bool boolean);
 CJSON_PUBLIC(cJSON*) cJSON_AddNumberToObject(cJSON * const object, const char * const name, const double number);
+CJSON_PUBLIC(cJSON*) cJSON_AddNumberWithPrecisionToObject(cJSON * const object, const char * const name, const double n, int decimal_places);
 CJSON_PUBLIC(cJSON*) cJSON_AddStringToObject(cJSON * const object, const char * const name, const char * const string);
 CJSON_PUBLIC(cJSON*) cJSON_AddRawToObject(cJSON * const object, const char * const name, const char * const raw);
 CJSON_PUBLIC(cJSON*) cJSON_AddObjectToObject(cJSON * const object, const char * const name);

cJSON_Utils.c

@@ -840,7 +840,7 @@ static int apply_patch(cJSON *object, const cJSON *patch, const cJSON_bool case_
     {
         if (opcode == REMOVE)
         {
-            static const cJSON invalid = { NULL, NULL, NULL, cJSON_Invalid, NULL, 0, 0, NULL};
+            static const cJSON invalid = { NULL, NULL, NULL, cJSON_Invalid, NULL, 0, 0, 0, NULL};
 
             overwrite_item(object, invalid);
 

tests/cjson_add.c

@@ -255,6 +255,44 @@ static void cjson_add_number_should_add_number(void)
     cJSON_Delete(root);
 }
 
+static void assert_add_number_with_precision_prints(const char *expected, double number, int decimal_places)
+{
+    cJSON *root = cJSON_CreateObject();
+    char *printed = NULL;
+
+    TEST_ASSERT_NOT_NULL(cJSON_AddNumberWithPrecisionToObject(root, "number", number, decimal_places));
+
+    printed = cJSON_PrintUnformatted(root);
+    TEST_ASSERT_EQUAL_STRING(expected, printed);
+
+    cJSON_free(printed);
+    cJSON_Delete(root);
+}
+
+static void cjson_add_number_with_precision_should_format_output(void)
+{
+    assert_add_number_with_precision_prints("{\"number\":1.20}", 1.2, 2);
+    assert_add_number_with_precision_prints("{\"number\":1.24}", 1.236, 2);
+    assert_add_number_with_precision_prints("{\"number\":-1.200}", -1.2, 3);
+    assert_add_number_with_precision_prints("{\"number\":3}", 3.0, 5);
+    assert_add_number_with_precision_prints("{\"number\":0.12345678901234}", 0.12345678901234, 14);
+}
+
+static void cjson_add_number_with_precision_should_reject_invalid_precision(void)
+{
+    cJSON *root = cJSON_CreateObject();
+    char *printed = NULL;
+
+    TEST_ASSERT_NULL(cJSON_AddNumberWithPrecisionToObject(root, "number", 1.2, 0));
+    TEST_ASSERT_NULL(cJSON_AddNumberWithPrecisionToObject(root, "number", 1.2, 15));
+
+    printed = cJSON_PrintUnformatted(root);
+    TEST_ASSERT_EQUAL_STRING("{}", printed);
+
+    cJSON_free(printed);
+    cJSON_Delete(root);
+}
+
 static void cjson_add_number_should_fail_with_null_pointers(void)
 {
     cJSON *root = cJSON_CreateObject();
@@ -448,6 +486,8 @@ int CJSON_CDECL main(void)
     RUN_TEST(cjson_add_bool_should_fail_on_allocation_failure);
 
     RUN_TEST(cjson_add_number_should_add_number);
+    RUN_TEST(cjson_add_number_with_precision_should_format_output);
+    RUN_TEST(cjson_add_number_with_precision_should_reject_invalid_precision);
     RUN_TEST(cjson_add_number_should_fail_with_null_pointers);
     RUN_TEST(cjson_add_number_should_fail_on_allocation_failure);
 

tests/misc_tests.c

@@ -239,7 +239,7 @@ static void cjson_should_not_follow_too_deep_circular_references(void)
 
 static void cjson_set_number_value_should_set_numbers(void)
 {
-    cJSON number[1] = {{NULL, NULL, NULL, cJSON_Number, NULL, 0, 0, NULL}};
+    cJSON number[1] = {{NULL, NULL, NULL, cJSON_Number, NULL, 0, 0, 0, NULL}};
 
     cJSON_SetNumberValue(number, 1.5);
     TEST_ASSERT_EQUAL(1, number->valueint);
@@ -361,7 +361,7 @@ static void cjson_replace_item_via_pointer_should_replace_items(void)
 
 static void cjson_replace_item_in_object_should_preserve_name(void)
 {
-    cJSON root[1] = {{NULL, NULL, NULL, 0, NULL, 0, 0, NULL}};
+    cJSON root[1] = {{NULL, NULL, NULL, 0, NULL, 0, 0, 0, NULL}};
     cJSON *child = NULL;
     cJSON *replacement = NULL;
     cJSON_bool flag = false;

tests/readme_examples.c

@@ -165,6 +165,34 @@ static char *create_monitor_with_helpers(void)
     return string;
 }
 
+/* Returns a heap-allocated string that must be released with cJSON_free. */
+static char *create_numbers_with_precision(void)
+{
+    char *string = NULL;
+    cJSON *object = cJSON_CreateObject();
+
+    if (object == NULL)
+    {
+        return NULL;
+    }
+
+    if (cJSON_AddNumberWithPrecisionToObject(object, "pi", 3.141592653589793, 6) == NULL)
+    {
+        goto end;
+    }
+
+    if (cJSON_AddNumberWithPrecisionToObject(object, "integer", 3.0, 5) == NULL)
+    {
+        goto end;
+    }
+
+    string = cJSON_PrintUnformatted(object);
+
+end:
+    cJSON_Delete(object);
+    return string;
+}
+
 /* return 1 if the monitor supports full hd, 0 otherwise */
 static int supports_full_hd(const char * const monitor)
 {
@@ -232,6 +260,16 @@ static void create_monitor_with_helpers_should_create_a_monitor(void)
     free(monitor);
 }
 
+static void create_numbers_with_precision_should_round_and_preserve_integers(void)
+{
+    char *numbers = create_numbers_with_precision();
+
+    TEST_ASSERT_NOT_NULL(numbers);
+    TEST_ASSERT_EQUAL_STRING("{\"pi\":3.141593,\"integer\":3}", numbers);
+
+    cJSON_free(numbers);
+}
+
 static void supports_full_hd_should_check_for_full_hd_support(void)
 {
     static const char *monitor_without_hd = "{\n\
@@ -252,6 +290,7 @@ int CJSON_CDECL main(void)
 
     RUN_TEST(create_monitor_should_create_a_monitor);
     RUN_TEST(create_monitor_with_helpers_should_create_a_monitor);
+    RUN_TEST(create_numbers_with_precision_should_round_and_preserve_integers);
     RUN_TEST(supports_full_hd_should_check_for_full_hd_support);
 
     return UNITY_END();