Enum as parameter of function in C/C++

Question

Can somebody give me an example where we really need an enum to be a parameter in function?

I think you would better help yourself by asking a different question. The reason for using an enum as a function parameter is the same as the reason for using an enum anywhere else in your code. — Ben Cottrell, Sep 02 '12 at 08:21
"really need" is too strong; you never do, but using them can make your code clearer, easier to maintain, and less bug-prone (especially in C++) — Clifford, Sep 02 '12 at 10:51

juanchopanza · Answer 1 · 2012-09-02T11:13:46.563

5

Besides making code clearer, in C++ it enforces at compile time that a function only work with one out of a set of possible values:

namespace Foo
{
enum Bar { A, B, C };

void foo(Bar b) { .... }
void foo2(int i) { /* only ints between 0 and 5 make sense */ }
}


int main()
{
  Foo::Bar b = Foo::A;
  Foo::foo(b);   // OK
  Foo::foo(245); // Compile-time error!
  Foo::foo2(6);  // Compiles, triggering some run-time error or UB 
}

edited Sep 02 '12 at 11:13

answered Sep 02 '12 at 08:09

juanchopanza

223,364
34
402
480

True of C++ but not of C which does not enforce type checking of enum types. A C compiler may however issue a warning, but may not do so as described here: http://stackoverflow.com/questions/8597426/enum-type-check-in-c-gcc – Clifford Sep 02 '12 at 10:49
@Clifford thanks for pointing that out. I hadn't realised the question was about two different languages, which is nonsense. – juanchopanza Sep 02 '12 at 11:13
"nonsense" may be a bit strong - the languages share some identical syntax and are interoperable, it is perhaps naive but not unreasonable to assume identical semantics for the same syntax - the gotcha being they are not identical. – Clifford Sep 02 '12 at 12:00

score 2 · Answer 2 · answered Sep 02 '12 at 08:07

2

There is no need for enums, but they make software more readable. Example:

void write( const std::string&, bool flush );

And now the calling side:

write( "Hello World", true );

If an enum had been used, on the calling side it becomes more clearly what the second parameter means:

enum flush_type { flush, no_flush };
void write( const std::string&, flush_type flush );

and again the calling side:

write( "Hello World", flush );

answered Sep 02 '12 at 08:07

Torsten Robitzki

3,041
1
21
35

1

Not really, the use of enumerations limits what you can pass as function argument to values of the enumeration. – juanchopanza Sep 02 '12 at 08:11
@juanchopanza: Exactly. What should the function do with an unanticipated value? Enums help clarify what the function has been designed to do. – Pontus Gagge Sep 02 '12 at 08:14
@PontusGagge and may force a compiler error, as in the example in my answer. – juanchopanza Sep 02 '12 at 08:15
@juanchopanza: Only forces an error in C++. – Clifford Sep 02 '12 at 10:53

score 0 · Answer 3 · answered Sep 02 '12 at 08:10

0

The function setColor in button, need to get parameter color, which sould be enum.

answered Sep 02 '12 at 08:10

LeeNeverGup

1,096
8
23

Note that every enum is equivalet to consts in the machine language – LeeNeverGup Sep 02 '12 at 08:13

Enum as parameter of function in C/C++

3 Answers3