C++ compilation error: Undefined structure assignment cannot be made, how to solve it?

It is very common for errors to occur when compiling C programs. One of the common errors is "undefined structure assignment cannot be made". This error is usually caused by calling an undefined or undeclared structure variable in the program, causing the compiler to be unable to perform the structure assignment operation.

To solve this problem, we need to better understand the relevant knowledge of structures and structure assignments, and choose different solutions for different situations. Below, we will introduce in detail how to solve the problem of "undefined structure assignment cannot be performed".

1. Understand structure and structure assignment

Structure is a very important data type in C, which is usually used to describe some complex entity objects. In C, structures can contain variables of different types, such as integer, floating point, character, etc.

Structure assignment refers to assigning the value of one structure variable to another structure variable, such as:

struct person
{
    int age;
    char name[20];
};

int main()
{
    person p1, p2;
    p1.age = 20;
    strcpy(p1.name, "Jack");
    p2 = p1; //结构体赋值
    return 0;
}

In the above example, we defined a person structure, Contains two variables, age and name. Then, we defined two person type variables p1 and p2 in the main function. After assigning a value to p1, we assigned its value to p2. This is the structure assignment operation.

2. Methods to solve "Undefined structure assignment cannot be performed"

1. Check whether the structure definition is correct

A common reason is that an undefined structure is called. Defined or undeclared structure variables. If we use an undefined or undeclared structure variable, the compiler will not be able to perform structure assignment, and will report the error "Cannot perform undefined structure assignment".

So, when we encounter this error, we first need to check whether the structure we use has been correctly defined. We can check the following points:

(1) Whether the name of the structure is correct;

(2) Whether the syntax of the structure definition is correct;

(3) Whether Define the structure variable before using it.

If there is an error when defining the structure, we should correct the error in time and recompile the program.

2. Check whether the structure variable is named correctly

In the program, when we define variables, we need to pay attention to the uniqueness of the variable name and cannot define it repeatedly. If we name a structure variable the same as another variable, the compiler will not be able to recognize the object we assign and will report the error "Undefined structure assignment cannot be made".

Therefore, we need to check whether the variable name is unique. If there are duplicate variable names, we should modify and recompile the program in time.

3. Confirm that the structure variable is defined in the appropriate location

In C, the structure variable must be defined before use, otherwise the compiler will not be able to perform structure assignment. Therefore, when the "Cannot assign to undefined structure" error occurs, we need to check whether our structure variables are defined in the correct location. Specifically, we need to ensure the following points:

(1) Whether the structure variable is defined before use;

(2) Whether the structure variable is correctly scoped Including;

(3)Whether the structure variables are initialized correctly.

If we find that there is a problem with the location of the structure variable definition, we should put it in the correct location and recompile the program.

4. Use structure pointers correctly in programs

In C, we can perform structure assignment operations by defining pointers pointing to structures. However, if an error occurs when using pointers, the compiler will be unable to perform structure assignment and report an error "Cannot perform undefined structure assignment".

Therefore, when using structure pointers, we need to pay attention to some issues:

(1) Whether the structure pointed to by the pointer has been correctly defined;

(2) Whether the pointer has been correctly initialized or assigned;

(3) Whether the structure assignment is performed before the pointer points to the structure.

If these problems exist, we need to stop using structure pointers and modify the program.

3. Summary

During the compilation process of C program, it is a very common situation that the error "cannot assign an undefined structure" appears. If we encounter this kind of error, we need to carefully analyze the cause and choose the correct solution according to different situations. Through this article, I believe everyone has understood how to correctly solve the "undefined structure assignment cannot be performed" error.

The above is the detailed content of C++ compilation error: Undefined structure assignment cannot be made, how to solve it?. For more information, please follow other related articles on the PHP Chinese website!