C++ compilation error: The template parameter is not applicable to this type. How should I modify it?

C is a widely used programming language with many templates that allow programmers to quickly create codes that are common to various data types and algorithms. However, you will also encounter some compilation errors when using templates, one of which is "template parameters are not applicable to this type". This article will detail the background, causes, and solutions to this error.

Background

Template in C is a general programming pattern that can be used to generate a variety of different types of code. For example, we can use templates to create a general function that can receive different types of parameters and dynamically call different codes based on the type.

Template parameters in C are divided into two types: type parameters and non-type parameters. Type parameters refer to the data type to be used in the template, while non-type parameters refer to some constants or function pointers, etc. These parameters must be determined at compile time.

Normally, the type parameters used in the template should be applicable to various data types, but sometimes a compilation error occurs, prompting "the template parameters are not applicable to this type." Next, we will introduce the causes and solutions of this error.

Cause

The template parameter is not applicable to this type error is usually caused by the following reasons:

1. Template parameter type mismatch:

When we define a template, the type of the template parameters should conform to the data type we require to pass in. If the data type passed in does not match the template parameter type, an error will be reported.

For example, in the following code, we define a template function and use the template parameter T inside the function:

template <typename T>
void print(T value) {
    cout << value << endl;
}

Then we call this function and pass in a string as a parameter, An error will be reported:

print("hello");  // 模板参数不适用于这个类型

This is because the parameter type in the template function must be the same as the type of the incoming parameter. What is passed in here is a string constant, and the template parameter type is T, so it appears. mistake.

2. The type is not defined:

When we use an undefined type as a template parameter, the compiler cannot find the type and will report an error.

For example, in the following code, we define a template class that uses an undefined type parameter:

template <typename T>
class Test {
public:
    void print(T value) {
        cout << value << endl;
    }
};

int main() {
    Test<UnknownType> a; // 模板参数不适用于这个类型
    return 0;
}

In the above code, we define an undefined type named UnknownType Define the type and pass it as a template parameter when defining a template class, which will cause an error at compile time.

3. Template parameters do not meet the requirements:

Sometimes we will add some restrictions to the template parameters, such as only allowing certain data types to be passed in. When the data type we pass in does not meet the restrictions, an error will be reported.

For example, in the following code, we define a template function that only allows integer type parameters to be passed in:

template <typename T>
void print(T value) {
    static_assert(is_integral<T>::value, "只允许传入整数类型的参数");
    cout << value << endl;
}

int main() {
    print(3.14); // 模板参数不适用于这个类型
    return 0;
}

In the above code, we use the is_integral template to determine the template parameter type Whether it is an integer type, if not, an error message will be printed. When calling the print function, we pass in floating-point parameters, which will cause compilation to fail.

Solution

When a compilation error occurs that the template parameter is not suitable for this type, we can try the following solutions:

1. Confirm the template parameter type Whether it matches the incoming parameter type

When this error occurs, you should first check whether the template parameter type and the incoming parameter type match. If they do not match, they need to be modified.

2. Confirm whether the type used has been defined

If an undefined type is used as a template parameter, you need to define the type in the program or use a defined type type.

3. Confirm whether the template parameters meet the requirements

When using a template with restrictions, you should ensure that the parameter types passed in meet the requirements. If it does not comply, you need to modify the parameter type or modify the restrictions.

Summary

Template is a very important feature in C, which allows us to write general code more flexibly. However, when using templates, you will also encounter some compilation errors, one of which is "template parameters are not applicable to this type". This article introduces the causes and solutions of this error with code examples, hoping to help readers better understand and use C templates.

The above is the detailed content of C++ compilation error: The template parameter is not applicable to this type. How should I modify it?. For more information, please follow other related articles on the PHP Chinese website!