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print: support float pretty print

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Code below:

float a = 0.00001;
cJSON *root = cJSON_CreateObject();
cJSON_AddNumberToObject(root, "a", a);
printf("%s\n", cJSON_Print(root));

Maybe it will print:
{
        "a":    9.9999997473787516e-06
}

But that's not what we really want, we want this:
{
	"a":    1e-5
}

Signed-off-by: dubaowei <517883875@qq.com>
This commit is contained in:
dubaowei 2021-12-20 19:12:58 +08:00
parent 203a0dec6f
commit 3cd7b59a0c
1 changed files with 17 additions and 4 deletions
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15
cJSON.c
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@ -535,6 +535,11 @@ static void update_offset(printbuffer * const buffer)
} }
/* securely comparison of floating-point variables */ /* securely comparison of floating-point variables */
static cJSON_bool compare_float(float a, float b)
{
float maxVal = fabs(a) > fabs(b) ? fabs(a) : fabs(b);
return (fabs(a - b) <= maxVal * FLT_EPSILON);
}
static cJSON_bool compare_double(double a, double b) static cJSON_bool compare_double(double a, double b)
{ {
double maxVal = fabs(a) > fabs(b) ? fabs(a) : fabs(b); double maxVal = fabs(a) > fabs(b) ? fabs(a) : fabs(b);
@ -550,6 +555,7 @@ static cJSON_bool print_number(const cJSON * const item, printbuffer * const out
size_t i = 0; size_t i = 0;
unsigned char number_buffer[26] = {0}; /* temporary buffer to print the number into */ unsigned char number_buffer[26] = {0}; /* temporary buffer to print the number into */
unsigned char decimal_point = get_decimal_point(); unsigned char decimal_point = get_decimal_point();
float test_f = 0.0;
double test = 0.0; double test = 0.0;
if (output_buffer == NULL) if (output_buffer == NULL)
@ -564,7 +570,13 @@ static cJSON_bool print_number(const cJSON * const item, printbuffer * const out
} }
else else
{ {
/* Try 15 decimal places of precision to avoid nonsignificant nonzero digits */ /* Try 7 decimal places of precision to avoid nonsignificant nonzero digits */
length = sprintf((char*)number_buffer, "%1.7g", (float)d);
/* Check whether the original double can be recovered */
if ((sscanf((char*)number_buffer, "%g", &test_f) != 1) || !compare_float(test_f, (float)d))
{
/* If not, print with 17 decimal places of precision */
length = sprintf((char*)number_buffer, "%1.15g", d); length = sprintf((char*)number_buffer, "%1.15g", d);
/* Check whether the original double can be recovered */ /* Check whether the original double can be recovered */
@ -574,6 +586,7 @@ static cJSON_bool print_number(const cJSON * const item, printbuffer * const out
length = sprintf((char*)number_buffer, "%1.17g", d); length = sprintf((char*)number_buffer, "%1.17g", d);
} }
} }
}
/* sprintf failed or buffer overrun occurred */ /* sprintf failed or buffer overrun occurred */
if ((length < 0) || (length > (int)(sizeof(number_buffer) - 1))) if ((length < 0) || (length > (int)(sizeof(number_buffer) - 1)))