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Matthew Layton
Matthew Layton

Reputation: 42260

Implicit enum values in C++

I am working on porting some interop code from the DWM Api in C++ to C#. The DWMWINDOWATTRIBUTE enum only explicitly defines, one value, and I want to know if the remaining values (commented) are correct?

typedef enum _DWMWINDOWATTRIBUTE { 
  DWMWA_NCRENDERING_ENABLED          =  1,
  DWMWA_NCRENDERING_POLICY,          // 2
  DWMWA_TRANSITIONS_FORCEDISABLED,   // 3
  DWMWA_ALLOW_NCPAINT,               // 4
  DWMWA_CAPTION_BUTTON_BOUNDS,       // 5
  DWMWA_NONCLIENT_RTL_LAYOUT,        // 6
  DWMWA_FORCE_ICONIC_REPRESENTATION, // 7
  DWMWA_FLIP3D_POLICY,               // 8
  DWMWA_EXTENDED_FRAME_BOUNDS,       // 9
  DWMWA_HAS_ICONIC_BITMAP,           // 10
  DWMWA_DISALLOW_PEEK,               // 11
  DWMWA_EXCLUDED_FROM_PEEK,          // 12
  DWMWA_CLOAK,                       // 13
  DWMWA_CLOAKED,                     // 14
  DWMWA_FREEZE_REPRESENTATION,       // 15
  DWMWA_LAST                         // 16
} DWMWINDOWATTRIBUTE;

Upvotes: 1

Views: 1239

Answers (3)

juanchopanza
juanchopanza

Reputation: 227410

Yes, in the C++03 and C++11 standards, 7.2 Enumeration declarations [dcl.enum]:

...An enumerator-definition without an initializer gives the enumerator the value obtained by increasing the value of the previous enumerator by one.

Also note that, in the absence of an initializer, the first enum value is 0. From the same section:

If the first enumerator has no initializer, the value of the corresponding constant is zero.

Upvotes: 5

Syed Mauze Rehan
Syed Mauze Rehan

Reputation: 1145

Yes that is correct, if you provide a value for the first entry then all the next entries are obtained by increasing the value of the prev enum by 1.

In this case, since you gave the first enum entry a value the next entries are 2,3,4,... respectively.

If you don't provide it, then it starts with a 0 (by default)

Upvotes: 1

Farzan Hajian
Farzan Hajian

Reputation: 2019

Yes enum values are incremented automatically. In C# you can also use the same syntax

public enum _DWMWINDOWATTRIBUTE { DWMWA_NCRENDERING_ENABLED = 1,...}

Upvotes: 1

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