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Re: Improper use of Null [message #52331 is a reply to message #52318]

Mon, 09 September 2019 20:23

Sender Ghost
Messages: 301
Registered: November 2008

Senior Member

Hello Iñaki.

I think, there is some explanation in "U++ Core Tutorial" about int and int64 types, where Null "defined as lowest number the type can represent".

Following example may show how it works:

#include <Core/Core.h>
#include <iostream>

using namespace Upp;

CONSOLE_APP_MAIN
{
	int i = Null;
	int64 i64 = Null;
	double d = Null;
	Value v = Null;

	std::cout << "i = " << i << std::endl
		<< "i64 = " << i64 << std::endl
		<< "d = " << d << std::endl
		<< "v = " << ~AsString(v) << std::endl;

	if ((i == i64) && (i64 == d) && (d == v))
		NEVER();
	else
		Cout() << "This is how it works\n";

	Value vi = i,
		vi64 = i64,
		vd = d,
		vv = v;

	if ((vi == vi64) && (vi64 == vd) && (vd == vv))
		Cout() << "This is how it works\n";
	else
		NEVER();
}

With following results:

i = -2147483648
i64 = -9223372036854775808
d = -1e+308
v = 
This is how it works
This is how it works

where i is assigned to INT_NULL (equal to INT_MIN) and i64 is assigned to INT64_NULL (equal to INT64_MIN) values. In other words, i > i64 and int64 type may include INT_NULL (which is not equal to INT64_NULL) in its range.

I guess, possible to use Value type for intermediate Null value, e.g. to "transfer" Null value from some type to another type:

#include <Core/Core.h>

using namespace Upp;

CONSOLE_APP_MAIN
{
	int a = Null;
	int64 b = Value(a);

	if (IsNull(b))
		Cout() << "I wanted this\n";
	else
		Cout() << "Oh no!\n";
}

Other examples

#include <Core/Core.h>

using namespace Upp;

#define PRINT_RESULT(x) \
	if (IsNull(x)) \
		Cout() << "I wanted this\n"; \
	else \
		Cout() << "Oh no!\n";

#define TEST1(type) { \
	Cout() << typeid(type).name() << ": "; \
	int a = Null; \
	type b = a; \
	PRINT_RESULT(b); \
}

#define TEST2(type) { \
	Cout() << typeid(type).name() << ": "; \
	int a = Null; \
	type b = IsNull(a) ? Null : a; \
	PRINT_RESULT(b); \
}

#define TEST3(type) { \
	Cout() << typeid(type).name() << ": "; \
	int a = Null; \
	type b; \
	if (IsNull(a)) \
		b = Null; \
	else \
		b = a; \
	PRINT_RESULT(b); \
}

#define TEST4(type) { \
	Cout() << typeid(type).name() << ": "; \
	int a = Null; \
	type b = Value(a); \
	PRINT_RESULT(b); \
}

#define TYPES(d) Cout() << #d << '\n'; \
	d(int); \
	d(int64); \
	d(double); \
	d(Value);

CONSOLE_APP_MAIN
{
	TYPES(TEST1);
	TYPES(TEST2);
	TYPES(TEST3);
	TYPES(TEST4);
}

Results:

TEST1
i: I wanted this
x: Oh no!
d: Oh no!
N3Upp5ValueE: I wanted this
TEST2
i: I wanted this
x: Oh no!
d: Oh no!
N3Upp5ValueE: I wanted this
TEST3
i: I wanted this
x: I wanted this
d: I wanted this
N3Upp5ValueE: I wanted this
TEST4
i: I wanted this
x: I wanted this
d: I wanted this
N3Upp5ValueE: I wanted this

#include <Core/Core.h>

using namespace Upp;

CONSOLE_APP_MAIN
{
	int a = Null;
#if 1
	int64 b = a; // Not Null [*]
#elif 0
	double b = a; // Not Null [*]
#elif 0
	Value b = a; // Null [*]
#elif 0
	int64 b = Null; // Null
#elif 0
	double b = Null; // Null
#elif 0
	Value b = Null; // Null
#elif 0
	int64 b = IsNull(a) ? Null : a; // Not Null [*]
#elif 0
	double b = IsNull(a) ? Null : a; // Not Null [*]
#elif 0
	Value b = IsNull(a) ? Null : a; // Null [*]
#elif 0
	int64 b;
	if (IsNull(a))
		b = Null; // Null
	else
		b = a;
#elif 0
	double b;
	if (IsNull(a))
		b = Null; // Null
	else
		b = a;
#elif 0
	Value b;
	if (IsNull(a))
		b = Null; // Null
	else
		b = a;
#elif 0
	int64 b = IsNull(a) ? INT64_NULL : a; // Null
#else
	double b = IsNull(a) ? DOUBLE_NULL : a; // Null
#endif

	if (IsNull(b))
		Cout() << "I wanted this\n";
	else
		Cout() << "Oh no!\n";
}

[Updated on: Thu, 12 September 2019 16:45]

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