Solve the "error: expected casing-sequence before 'datatype'" problem in C++ code

Solve the "error: expected casing-sequence before 'datatype'" problem in C code

In the process of writing C code, we often encounter Various error messages, one of the common errors is "error: expected casing-sequence before 'datatype'". This error usually occurs when using custom data types or classes, and it means that the compiler cannot recognize the name of a certain data type or class.

In order to solve this problem, we need to first figure out the cause of this error. Generally speaking, this error is caused by the following situations:

1. The header file is not introduced correctly
2. The name of the class or data type is spelled incorrectly
3. The same name There is a conflict in the variables or functions
4. The declaration order of the class or data type is wrong

Below we use some code examples to illustrate how to solve this problem:

1. The header file was not introduced correctly

#include <iostream>

int main() {
  // 假设我们在这里使用了一个自定义的数据类型Point
  Point p;
  // ...
  return 0;
}

In the above code, we wanted to use a custom data type Point, but we forgot to introduce the corresponding header file. At this time, the compiler will report an error and prompt "error: expected casing-sequence before 'Point'" because the compiler cannot find the definition of the Point data type. In order to solve this problem, we need to add the #include statement at the beginning of the code:

#include <iostream>
#include "point.h"

int main() {
  Point p;
  // ...
  return 0;
}

2. The name of the class or data type is misspelled

#include <iostream>

int main() {
  // 假设我们想要使用一个自定义的数据类型叫做MyData
  Mydata data;
  // ...
  return 0;
}

In the above code, we misspelled the name of the custom data type MyData as Mydata. The compiler will report an error and prompt "error: expected casing-sequence before 'data'" because the compiler cannot recognize the data type Mydata. In order to solve this problem, we only need to change the misspelling to the correct name:

#include <iostream>

int main() {
  MyData data;
  // ...
  return 0;
}

3. There is a conflict between variables or functions with the same name

#include <iostream>

int main() {
  // 假设我们在这里定义了一个同名的变量
  Point Point;
  // ...
  return 0;
}

Above In the code, we defined a variable Point with the same name in the main function, which conflicts with the custom data type Point. The compiler will report an error and prompt "error: expected casing-sequence before 'Point'" because the compiler cannot distinguish whether it is a variable or a data type. In order to solve this problem, we need to modify the name of the variable to avoid duplication with the data type name:

#include <iostream>

int main() {
  Point myPoint;
  // ...
  return 0;
}

4. The declaration order of the class or data type is wrong

#include <iostream>

class Point {
private:
  int x;
  int y;
public:
  Point(int a, int b) {
    x = a;
    y = b;
  }
};

int main() {
  Point p(1, 2);
  // ...
  return 0;
}

The above code , we defined the main function before using the custom data type Point. At this time, the compiler will report an error and prompt "error: expected casing-sequence before 'Point'" because the compiler cannot find the definition of the Point data type in the main function. In order to solve this problem, we need to place the definition of the custom data type before the main function:

#include <iostream>

class Point {
private:
  int x;
  int y;
public:
  Point(int a, int b) {
    x = a;
    y = b;
  }
};

int main() {
  Point p(1, 2);
  // ...
  return 0;
}

Through the above example, we can see that solving "error: expected casing-sequence before 'datatype'" The main methods to solve the problem are to check the introduction of header files, the spelling of names, avoid conflicts between variables and functions with the same name, and the declaration order of classes or data types. As long as you find the cause of the error based on the specific error message and make appropriate modifications, you can solve the problem. Hope this article can be helpful to readers.

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