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Home Backend Development C++ How to solve C++ syntax error: 'expected primary-expression before '.' token'?

How to solve C++ syntax error: 'expected primary-expression before '.' token'?

Aug 26, 2023 pm 07:43 PM
c++ syntax error primary-expression '' token

如何解決C++語法錯誤:\'expected primary-expression before \'.\' token\'?

How to solve C syntax error: 'expected primary-expression before '.' token'?

When writing programs in C, we sometimes encounter various syntax errors. One of the common errors is 'expected primary-expression before '.' token'. When we use incorrect syntax to access members of a class in our code, the compiler will report this error.

This error is usually caused by the following reasons:

  1. Incorrectly using the dot operator (.) to access a member variable or member function of a non-class object.
  2. Incorrectly used the dot operator (.) to access a member variable or member function of a pointer object instead of using the arrow operator (->).
  3. When we use an undeclared or undefined class object as a prefix for a member variable or member function, the compiler cannot recognize the object.

Here are some sample codes to illustrate how to solve this error:

Example 1:

#include <iostream>
using namespace std;

int main() {
    int length = 10;
    cout.length;  // 錯誤:應該使用點運算符來訪問一個類對象的成員
    return 0;
}

Fix: Change cout.length to cout<

Example 2:

#include <iostream>
using namespace std;

class MyClass {
public:
    void printHello() {
        cout<<"Hello"<<endl;
    }
};

int main() {
    MyClass* myObject;
    myObject.printHello();  // 錯誤:應該使用箭頭運算符來訪問指針對象的成員
    return 0;
}

Fixation method: Modify myObject.printHello() to myObject->printHello().

Example 3:

#include <iostream>
using namespace std;

class MyClass {
public:
    void printHello() {
        cout<<"Hello"<<endl;
    }
};

int main() {
    MyClass myObject;
    MyObject.printHello();  // 錯誤:使用了未定義的對象
    return 0;
}

Repair method: Modify MyObject.printHello() to myObject.printHello().

Through the above repair methods, we can solve the 'expected primary-expression before '.' token' error. It should be noted that the solution to this error is to fix it according to the specific code situation and ensure that the correct syntax is used to access the members of the class. At the same time, when writing code, we must also carefully check and review the code to avoid such common grammatical errors to improve the quality and stability of the program.

To summarize, the 'expected primary-expression before '.' token' error is caused by using incorrect syntax when accessing members of the class. We can easily resolve this error by declaring and defining class objects using the correct use of dot and arrow operators. When we encounter such errors, we can carefully check the code and make repairs according to the specific situation to ensure the normal operation of the program.

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