C++ – Compile and link multiple files

March 11, 2022

I have a project with the following structure:

Item.cpp
Item.h
main.cpp
Makefile

The following source code is in the Item.h file:

class Item {
    public:
        Item();
        ~Item();
};

The following source code is in the Item.cpp file:

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

Item::Item() {
    std::cout << "Item created..." << std::endl;
}

Item::~Item() {
    std::cout << "Item destroyed..." << std::endl;
}

The following source code is the content of the main.cpp file:

#include "Item.h"

#include <iostream>


int main() {
    std::cout << "Initialize program..." << std::endl;
    Item item_1();
    std::cout << "Hello world!" << std::endl;

    return 0;
}

And finally, the following source code is the Makefile file:

CXX = g++

all: main item
    $(CXX) -o sales.o main.o Item.o

main:
    $(CXX) -c main.cpp

item:
    $(CXX) -c Item.cpp

clean:
    rm -rf *.o

When I run the make command and then I run the compiled code with the command ./sales.o, I get the following output:

Initialize program...
Hello world!

Why is the output of the constructor method of the class Item not printed in the console? I found in some web pages that you can compile the source codes in steps and then you can link it with the -o option when using g++ but it does not work in this case. How can I compile this source codes step by step and then link it in the Makefile?

>Solution :

I’m surely you ignored this warning :

warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]

#include "Item.h"

#include <iostream>


int main() {
    std::cout << "Initialize program..." << std::endl;
    Item item_1;
    std::cout << "Hello world!" << std::endl;

    return 0;
}

just remove parentheses it will be work
test : https://godbolt.org/z/KrdrhvsrW