Header file duplicate definition problem solving "c1014 error“

For example, now there are three files , Two header files , One .cpp file
header1.h

#include "header2.h"

int fun2();

header2.h

#include "header1.h"

int fun();

main.cpp

#include "header1.h"

int main()
{
    
	return 0;
}

The compiler will replace the header file in the preprocessing process , Finally, the following code is formed , The header file 1 Include header file 2, The header file 2 Also includes header file 1, Nesting with each other , This is the compiler will report an error “C1014 Contains too many files : depth = 1024 ”

#include "header1.h"
...
int fun();

int fun2();

int main()
{
    
	return 0;
}

There are two solutions ：

• One is #ifndef solve
  But this name is customized , There may be the same time , For example, two files are written at the same time HEADER_1, This will reduce the number of header files , Therefore, it is suggested to adopt the second

header1.h

#ifndef HEADER_1
#define HEADER_1
#include "header2.h"

int fun2();
#endif

header2.h

#ifndef HEADER_2
#define HEADER_2
#include "header1.h"

int fun();
#endif

main.cpp

#include "header1.h"

int main()
{
    
	return 0;
}

After the header file is expanded

#define HEADER_1
#define HEADER_2

#ifndef HEADER_1
#define HEADER_1
#include "header2.h"

int fun2();
#endif

int fun();

int fun2();

int main()
{
    
	return 0;
}

• The other is to adopt #pragma once
  The principle of this implementation is , There will be a count inside , Indicates that this header file will only be expanded once

header1.h

#pragma once
#include "header2.h"

int fun2();

header2.h

#pragma once
#include "header1.h"

int fun();

main.cpp

#include "header1.h"

int main()
{
    
	return 0;
}