There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:
// File1.cs
using System;
namespace Outer.Inner
{
class Foo
{
static void Bar()
{
double d = Math.PI;
}
}
}
Now imagine that someone adds another file (File2.cs) to the project that looks like this:
// File2.cs
namespace Outer
{
class Math
{
}
}
The compiler searches Outer
before looking at those using
directives outside the namespace, so it finds Outer.Math
instead of System.Math
. Unfortunately (or perhaps fortunately?), Outer.Math
has no PI
member, so File1 is now broken.
This changes if you put the using
inside your namespace declaration, as follows:
// File1b.cs
namespace Outer.Inner
{
using System;
class Foo
{
static void Bar()
{
double d = Math.PI;
}
}
}
Now the compiler searches System
before searching Outer
, finds System.Math
, and all is well.
Some would argue that Math
might be a bad name for a user-defined class, since there's already one in System
; the point here is just that there is a difference, and it affects the maintainability of your code.
It's also interesting to note what happens if Foo
is in namespace Outer
, rather than Outer.Inner
. In that case, adding Outer.Math
in File2 breaks File1 regardless of where the using
goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using
directive.
Best Answer
This usually occurs when your oracle client is not in the PATH of your computer.
Make sure that the
PATH
environment variable contains both<Oracle client path>
and<Oracle client path>\bin
.Also, this can happen if the
SID
of the database you want to connect to is simply not defined in thetnsnames.ora
file under your oracle client installation path. If I recall correctly - it is under<Oracle client path>\network\admin\tnsnames.ora
Edit: The registry should contain an ORACLE entry set under:
HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\
There should be a key named
HOME0
with string values: ORACLE_HOME and ID. I assume there are other values required as well - but those two I'm sure of. Check that ORACLE_HOME points correctly to the oracle client location.