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i'm new to compiling c ++ programs with makefile on linux. trying to include a header file inside another the compiler gives me the following error:

In file included from main.cpp:5:
send_file.hpp:2:10: fatal error: connection.hpp: No such file or directory
    2 | #include <connection.hpp>
      |          ^~~~~~~~~~~~~~~~
compilation terminated.
make: *** [makefile:5: main.o] Error 1

This is the send_file.hpp file:

#include <string>
#include <connection.hpp>
using namespace std;

class SendFile
{
public:
    static bool send_file(string filename, Connection *connection);
};

This is the connection.hpp file

#pragma once

#include <string>
#include <sys/types.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <exception>
using namespace std;
#define PORT 12345

class Connection
{
public:
    Connection();
    Connection(string ip_addr, string filename);
    void set_ip_address(string ip_addr);
    void set_filename(string filename);
    string get_ip_address();
    string get_filename();
    bool open_connection();
    bool send_string(string msg);
private:
    string ip_addr;
    string filename;
    sockaddr_in server_addr;// server's IP address
    int client_sock;
};

and, finally this is makefile

output: main.o ipaddress.o file.o connection.o send_file.o
    g++ main.o ipaddress.o file.o connection.o send_file.o -o output

main.o: main.cpp
    g++ -c main.cpp

ipaddress.o: ipaddress.cpp ipaddress.hpp
    g++ -c ipaddress.cpp

file.o: file.cpp file.hpp
    g++ -c file.cpp

connection.o: connection.cpp connection.hpp
    g++ -c connection.cpp

send_file.o: send_file.cpp send_file.hpp
    g++ -c send_file.cpp

target: dependencies
    action

clean:
    rm *.o

thank you very much for helping

Davide Bianchi
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    Btw: If you're using `#include "..."` instead of `#include <...>` files are searched relative to the current source file first and not searched in system directories, which is what I'd recommend doing for your own headers here, since every source is in the same dir. This has the added benefit of enabling IDEs to find the headers even if they don't have access to the info in the makefile. – fabian Aug 20 '22 at 10:18
  • `make` includes good default rules which you should take advantage of. If you delete your recipe for `main`, the default rules will work if you simply use `make CPPFLAGS=-I. main`. If you delete most of the rules, you will get better behavior. Honestly, your makefile should be one line: `output: main.o ipaddress.o file.o connection.o send_file.o`. – William Pursell Aug 20 '22 at 12:53

1 Answers1

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I usually employ the template below for Makefile (adapted to the names of your files).

I believe main.o should be created last, after all the dependencies it uses. Same for modules that are dependencies of some other modules.

CXX = g++
CXXFLAGS = -Wall

OBJECTS = ipaddress.o file.o connection.o send_file.o main.o

main: $(OBJECTS)
        $(CXX) $(CXXFLAGS) -o $@ $^
        
$(OBJECTS): ipaddress.hpp file.hpp connection.hpp send_file.hpp
Giogre
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