C++ syntax error: Enumeration members must be unique, how should I modify it?

When we write a C program, we sometimes encounter the following error message:

"C syntax error: enumeration members must be unique"

This is because in the enumeration Within a type, the names of enumeration members must be unique and cannot be repeated.

So, how to correct this error? Several solutions are given below.

Method 1: Manually modify the names of enumeration members

The simplest method is to manually modify the names of enumeration members to ensure that they are unique. For example, change duplicate member names to different names.

For example, if we define an enumeration type that contains two members with the same member name, as shown below:

enum Fruit
{
    Banana,
    Apple,
    Strawberry,
    Apple
};

The compiler will prompt "C syntax Error: Enumeration members must be unique". We can change one of the member names to a different name, as shown below:

enum Fruit
{
    Banana,
    Apple,
    Strawberry,
    Orange
};

This will resolve this error.

Method 2: Use typedef to define a new enumeration type

If we don’t want to modify the original enumeration type, we can also use typedef to define a new enumeration type and replace the original Enum types renamed.

For example, we can rename the above Fruit enumeration type to FruitType:

typedef enum
{
    Banana,
    Apple,
    Strawberry,
    Apple
} FruitType;

In this way, FruitType can be used in the program to replace the original Fruit enumeration type.

Method 3: Use enumeration class

C 11 introduces the new feature of enum class (enum class), which can limit the namespace of enumeration members when defining the enumeration type, so that This can avoid naming conflict problems.

For example, we can use enum class to define an enumeration type named Fruit and limit the namespace of its members to Fruit:

enum class Fruit
{
    Banana,
    Apple,
    Strawberry,
    Apple
};

At this time, if we define two enumeration types with the same name member, the compiler will report an error instead of a warning.

Summary:

In C, enumeration members must be unique and cannot be repeated. If the compiler prompts "C syntax error: enumeration members must be unique", you can manually modify the enumeration member names, use typedef to define a new enumeration type, or use an enumeration class to solve the problem. The method of using enumeration classes is a new feature introduced in C 11, which can effectively avoid the problem of naming conflicts of enumeration members.

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