What is the purpose of this empty typedef statement?

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I am looking at a legacy VC++ ActiveX project and find these statements in a header file:

typedef enum CursorMode {Fixed, Floating, Snap};
typedef enum Crosshair  {XY, X, Y};

I got this warning message:

Warning	C4091	'typedef ': ignored on left of 'Crosshair' when no variable is declared	NTGraph	c:\demo_temp\ntgraph_src\ntgraphctl.h

what is the purpose or benefit to do this ? try to get some insights from gurus in this community...

Thanks a million!

What I have tried:

I removed these typedef keyword and compile the project, no more warnings...

Posted 3-Jan-21 10:59am

Southmountain

Updated 3-Jan-21 20:08pm

v2

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3 solutions

Solution 1

Enumeration declaration - cppreference.com[^]

A useful usage is to make comparisons or assignments easier to read. Like:

C++

if (myCursorMode == CursorMode.Fixed)
{
  //do whatever
}

or

C++

if (whatever condition)
{
  myCursorMode = CursorMode.Snap;
}

instead of:

C++

if (myCursorMode == 1)
{
  //do whatever
}

or

C++

if (whatever condition)
{
  myCursorMode = 3;
}

As you don't say anything about the warnings I suppose they were like:
"XXX being declared but never used"?

If not... only because now it compiles without warning doesn't necessarily mean that it will be correctly executed. It might be that you get a runtime exception.

Without more information... difficult to say what it was.

Posted 3-Jan-21 11:13am

Nelek

Comments

Southmountain 3-Jan-21 18:24pm

here is the warning message:

Warning	C4091	'typedef ': ignored on left of 'Crosshair' when no variable is declared	NTGraph	c:\demo_temp\ntgraph_src\ntgraphctl.h

Nelek 4-Jan-21 13:58pm

Read Solution 2 and 3, the warning is coming because the code is not in the correct order or the typdef is not needed.

CPallini 4-Jan-21 2:04am

5.

Nelek 4-Jan-21 13:23pm

Thanks Carlo

Solution 3

(In addition to other solutions...) Please note in C++ you don't need the typedef at all, in the enum declaration. Try, for instance

C++

#include <iostream>
using namespace std;

enum CursorMode {Fixed, Floating, Snap};

int main()
{
  cout << Floating << endl;
}

Posted 3-Jan-21 20:08pm

CPallini

Comments

Southmountain 4-Jan-21 15:08pm

got it. Thank you!

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OriginalGriff · Accepted Answer · 2021-01-03T11:21:00

Solution 2

Well, it won't compile, but apart from that ...

If you correct it:

typedef enum {Fixed, Floating, Snap} CursorMode;

All it's doing is declaring an enum that (in both cases) has three possible values, and using typedef to give it a type name that can be used like char, or int.

typedef enum {Fixed, Floating, Snap} CursorMode;
...
CursorMode cm = Floating;
cout << cm;

Posted 3-Jan-21 11:21am

OriginalGriff

Comments

Southmountain 3-Jan-21 18:27pm

thank you for your insight!

OriginalGriff 4-Jan-21 3:25am

You're welcome!

CPallini 4-Jan-21 2:02am

5.