Problems with linking inline functions in C++

Question

test2.h

#ifndef TEST2_H_INCLUDED
#define TEST2_H_INCLUDED
#include "test1.h"

inline int add(int,int);

#endif // TEST2_H_INCLUDED

test2.cpp

#include "test2.h"

inline int add(int a,int b){
    return a+b;
}

main.cpp

#include <iostream>
#include "test2.h"

int main()
{
    std::cout << add(1,2);
    return 0;
}

Eror:

warning: inline function add(int,int) used but never defined
undefined reference to add(int,int)
ld returned 1 exit status

But if I remove inline from the files, the code compiles and executes fine. What am I doing wrong?

Note: I have seen all the threads on stack overflow,although they were similar to my question, the answers could not solve my issue

Using the mingw compiler with Code Blocks

Answer 1

您必须在头文件中定义内联函数，更多信息请参见 https://stackoverflow.com/questions/5057021/why-are-c-inline-functions-in-the-header#:~:text=If% 20you%20want%20to%20put,compiler%20cannot%20inline%20the%20function 。

Answer 2

//test2.h
#ifndef TEST2_H_INCLUDED
#define TEST2_H_INCLUDED
#include "test1.h"

inline int add(int a,int b) {
    return a+b;
}

#endif // TEST2_H_INCLUDED