C++ compilation error: Wrong fully qualified type name, how to fix it?

C is an object-oriented programming language that is widely used to develop various types of applications. When writing C code, you often encounter compilation errors. Among them, "fully qualified type name error" is a common compilation error. This article will introduce the causes of this error and how to correct it.

Fully qualified type name refers to using a namespace to define the type name, for example:

namespace mynamespace {
    class MyClass {
    public:
        void myMethod();
    };
}

In the above code, mynamespace::MyClass is the fully qualified type name. When using a fully qualified type name, the namespace and type name must be used to identify the type. For example:

mynamespace::MyClass object;

A fully qualified type name error occurs if the wrong namespace or type name is used, or if the correct scope resolution operator is not used.

Here are some common examples of fully qualified type name errors:

1. Namespace error:

namespace yournamespace {
    class YourClass {
    public:
        void yourMethod();
    };
}

mynamespace::YourClass object;    // 错误：mynamespace中没有YourClass

In this example, we want to use YourClass class in yournamespace, but mistakenly added it to mynamespace. The compiler will prompt an error because there is no class named YourClass in mynamespace.

2. Type name error:

namespace mynamespace {
    class MyClass {
    public:
        void myMethod();
    };
}

mynamespace::MyOtherClass object;    // 错误：未定义类型MyOtherClass

In this example, we referenced a non-existent type name MyOtherClass. The compiler will issue an error because this type is not defined.

3. Scope resolution operator error:

namespace mynamespace {
    class MyClass {
    public:
        void myMethod();
    };
}

MyClass::myMethod() {    // 错误：要使用命名空间限定MyClass
    // ...
}

In this example, we defined a member function myMethod() outside the class definition, but did not use namespace qualification MyClass. The compiler will prompt an error because MyClass is defined in the namespace.

To solve the fully qualified type name error, you need to find the cause of the error and modify it. Based on the error message, the code can be analyzed and the location of the error can be found. Then, you can modify it by:

1. Confirm the correctness of the namespace and type name.
2. Use a namespace and type name to identify the type when using a fully qualified type name, for example:

mynamespace::MyClass object;

3. Use a namespace to qualify a class name when defining a member function , for example:

namespace mynamespace {
    class MyClass {
    public:
        void myMethod();
    };
}

void mynamespace::MyClass::myMethod() {
    // ...
}

With the above modifications, you can avoid fully qualified type name errors and compile C code smoothly.

In short, fully qualified type name errors are common compilation errors in C programming. To avoid this kind of error, you can pay attention to the correctness of the namespace and type name, and use the namespace and type name to identify the type when using a fully qualified type name. By carefully analyzing error messages and making necessary modifications, you can successfully compile C code and develop high-quality applications.

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