Thread: Why it give warning message, how will it remove

Code:

Test1.h
---------------------
#ifndef TEST1_H_
#define TEST1_H_

#include "Test2.h"

typedef struct _Test1{
    int a;
    int b;

    int (*add)(struct _Test1 *test1, struct _Test2 *test2);
}Test1;

Test1 newTest1();

#endif /* TEST1_H_ */

Test1.c
-----------------------------

#include "Test1.h"

static int test1_add(Test1 *test1, Test2 *test2){
    return (test1->a + test1->b) + (test2->c + test2->d);
}

Test1 newTest1(){
    Test1 test1;
    test1.a = 5;
    test1.b =6;
    test1.add = &test1_add;
    return test1;
}

Test2.h
------------------------

#ifndef TEST2_H_
#define TEST2_H_

#include "Test1.h"


typedef struct _Test2{
    int c;
    int d;

    int (*substract)(struct _Test2 *test2, struct _Test1 *test1);
}Test2;

Test2 newtest2();

#endif /* TEST2_H_ */

Test2.c
----------------------------------
#include "Test2.h"

static int test2_substract(Test2 *test2, Test1 *test1){
    return (test2->c + test2->d) - (test1->a + test1->b);
}

Test2 newtest2(){
    Test2 test2 ;
    test2.c = 15;
    test2.d = 25;
    test2.substract = &test2_substract;
    return test2;
}

MakeFile
--------------------------------
all:
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"Test1.d" -MT"Test1.d" -o "Test1.o" "Test1.c"
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"Test2.d" -MT"Test2.d" -o "Test2.o" "Test2.c"
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o "main.o" "main.c"

warning message:
-------------------------------
make all 
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"Test1.d" -MT"Test1.d" -o "Test1.o" "Test1.c"
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"Test2.d" -MT"Test2.d" -o "Test2.o" "Test2.c"
In file included from Test1.h:12,
                 from Test1.c:10:
Test2.h:18: warning: ‘struct _Test1.h declared inside parameter list
Test2.h:18: warning: its scope is only this definition or declaration, which is probably not what you want
In file included from Test2.h:12,
                 from Test2.c:9:
Test1.h:17: warning: ‘struct _Test2.h declared inside parameter list
Test1.h:17: warning: its scope is only this definition or declaration, which is probably not what you want
gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o "main.o" "main.c"
gcc -o RountStruct Test1.o Test2.o main.o
In file included from Test1.h:12,
                 from main.c:9:
Test2.h:18: warning: ‘struct _Test1.h declared inside parameter list
Test2.h:18: warning: its scope is only this definition or declaration, which is probably not what you want
main.c: In function ‘main’:
main.c:21: warning: passing argument 2 of ‘test2.substract’ from incompatible pointer type
        #gcc -o RountStruct Test1.o Test2.o main.o