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Home » Extra libraries, Code snippets, applications etc. » C++ language problems and code snippets » Dumb bug. Improper use of Null
| Dumb bug. Improper use of Null [message #52318] |
Thu, 05 September 2019 12:13  |
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koldo
Messages: 3432
Registered: August 2008
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Senior Veteran |
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int a = Null;
int64 b = a;
if (IsNull(b))
Cout() << "I wanted this";
else
Cout() << "Oh no!";
Best regards
Iñaki
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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
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Senior Member |
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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] Report message to a moderator |
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| Re: Improper use of Null [message #52333 is a reply to message #52332] |
Mon, 09 September 2019 22:27 |
Sender Ghost
Messages: 301
Registered: November 2008
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Senior Member |
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mirek wrote on Mon, 09 September 2019 18:59That said, perhaps we could introduce something like
int64 x = NvlTo<int64>(s);
Something like this?
#include <Core/Core.h>
using namespace Upp;
template <class T, class C>
T NvlTo(const C& x)
{
if (IsNull(x))
return Null;
return x;
};
template <class T>
void Print(const T& x)
{
if (IsNull(x))
Cout() << "I wanted this\n";
else
Cout() << x << '\n';
}
CONSOLE_APP_MAIN
{
#if 1
int a = Null;
int64 b = NvlTo<int64>(a);
Print(b);
a = -10;
b = NvlTo<int64>(a);
Print(b);
#else
int a = Null;
int64 b, c = 0;
const int n = 1000000000;
{
RTIMING("NvlTo");
for (int i = 0; i < n; ++i) {
b = NvlTo<int64>(a);
c += b + 1;
}
}
Print(c);
ASSERT(c == n);
c = 0;
{
RTIMING("Value");
for (int i = 0; i < n; ++i) {
b = Value(a);
c += b + 1;
}
}
Print(c);
ASSERT(c == n);
#endif
}
With following results:
I wanted this
-10
Thanks.
[Updated on: Tue, 10 September 2019 21:10] Report message to a moderator |
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| Re: Improper use of Null [message #52613 is a reply to message #52333] |
Wed, 30 October 2019 08:11 |
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koldo
Messages: 3432
Registered: August 2008
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Senior Veteran |
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"A ship in the beach is a lighthouse to the sea" 
Other scenario to watch out for:
MyFunction(double val) {
if (IsNull(val))
Cout() << "Null";
else
Cout() << "Not Null";
}
...
MyFunction(Null); // "Null"
MyFunction(false ? 1 : Null); // "Not Null". The call sets INT_NULL instead of DOUBLE_NULL
Best regards
Iñaki
[Updated on: Wed, 30 October 2019 08:12] Report message to a moderator |
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