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Add define to set significant digits when writing json floats and dou… #891

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Add define to set significant digits when writing json floats and dou… #891

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1 change: 1 addition & 0 deletions docs/guides/json.md
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Expand Up @@ -35,6 +35,7 @@ A `wvalue` can be treated as an object or even a list (setting a value by using

JSON does not allow floating point values like `NaN` or `INF`, Crow will output `null` instead of `NaN` or `INF` when converting `wvalue` to a string. (`{"Key": NaN}` becomes `{"Key": null}`)

To serialize `#!cpp float` and `#!cpp double` with a given number of significant digits, say 6 (the default), use the macros `#!cpp #define CROW_JSON_FLOAT_PRECISION 6` and `#!cpp #define CROW_JSON_DOUBLE_PRECISION 6`.
<br><br>

Additionally, a `wvalue` can be initialized as an object using an initializer list, an example object would be `wvalue x = {{"a", 1}, {"b", 2}}`. Or as a list using `wvalue x = json::wvalue::list({1, 2, 3})`, lists can include any type that `wvalue` supports.<br><br>
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17 changes: 13 additions & 4 deletions include/crow/json.h
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Expand Up @@ -2,6 +2,15 @@

//#define CROW_JSON_NO_ERROR_CHECK
//#define CROW_JSON_USE_MAP
//#define CROW_JSON_FLOAT_PRECISION FLT_DIG
//#define CROW_JSON_DOUBLE_PRECISION DBL_DIG

#ifndef CROW_JSON_FLOAT_PRECISION
#define CROW_JSON_FLOAT_PRECISION 6
#endif
#ifndef CROW_JSON_DOUBLE_PRECISION
#define CROW_JSON_DOUBLE_PRECISION 6
#endif

#include <string>
#ifdef CROW_JSON_USE_MAP
Expand Down Expand Up @@ -1874,17 +1883,17 @@ namespace crow // NOTE: Already documented in "crow/app.h"
if (v.nt == num_type::Double_precision_floating_point)
{
#ifdef _MSC_VER
sprintf_s(outbuf, sizeof(outbuf), "%.*g", DECIMAL_DIG, v.num.d);
sprintf_s(outbuf, sizeof(outbuf), "%.*g", CROW_JSON_DOUBLE_PRECISION, v.num.d);
#else
snprintf(outbuf, sizeof(outbuf), "%.*g", DECIMAL_DIG, v.num.d);
snprintf(outbuf, sizeof(outbuf), "%.*g", CROW_JSON_DOUBLE_PRECISION, v.num.d);
#endif
}
else
{
#ifdef _MSC_VER
sprintf_s(outbuf, sizeof(outbuf), "%f", v.num.d);
sprintf_s(outbuf, sizeof(outbuf), "%.*g", CROW_JSON_FLOAT_PRECISION, v.num.d);
#else
snprintf(outbuf, sizeof(outbuf), "%f", v.num.d);
snprintf(outbuf, sizeof(outbuf), "%.*g", CROW_JSON_FLOAT_PRECISION, v.num.d);
#endif
}
char *p = &outbuf[0], *o = nullptr; // o is the position of the first trailing 0
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36 changes: 26 additions & 10 deletions tests/unittest.cpp
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Expand Up @@ -1124,22 +1124,38 @@ TEST_CASE("json::wvalue::wvalue(std::int64_t)")

TEST_CASE("json::wvalue::wvalue(float)")
{
float f = 4.2;
json::wvalue value = f;
{
float f = 3.14159265359;
json::wvalue value = f;

CHECK(value.t() == json::type::Number);
CHECK(value.dump() == "4.2");
CHECK(value.t() == json::type::Number);
CHECK(value.dump() == "3.14159");
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this is only true for CROW_JSON_FLOAT_PRECISION = 6 , so shouldn't this be part of test equation?

}
{
float f = 314159265.359;
json::wvalue value = f;

CHECK(value.t() == json::type::Number);
CHECK(value.dump() == "3.14159e+08");
}
} // json::wvalue::wvalue(float)

TEST_CASE("json::wvalue::wvalue(double)")
{
double d = 0.036303908355795146;
json::wvalue value = d;
{
double d = 0.036303908355795146;
json::wvalue value = d;

CHECK(value.t() == json::type::Number);
auto dumped_value = value.dump();
CROW_LOG_DEBUG << dumped_value;
CHECK(std::abs(utility::lexical_cast<double>(dumped_value) - d) < numeric_limits<double>::epsilon());
CHECK(value.t() == json::type::Number);
CHECK(value.dump() == "0.0363039");
}
{
double d = 36303908355795.146;
json::wvalue value = d;

CHECK(value.t() == json::type::Number);
CHECK(value.dump() == "3.63039e+13");
}
} // json::wvalue::wvalue(double)

TEST_CASE("json::wvalue::wvalue(char const*)")
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