g++ using a object file in external directory

Question

Context:

I am current learning c/c++ compiling on my raspberry pi b+ model (started last week), but having trouble using a header file inside a object file.

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File locations:

main.cpp - ~/src/c++/projects/web_server

http_socket.o - ~/src/c++/web

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g++ output for g++ -o webserver ~/src/c++/web/http_socket.o -std=c++0x main.cpp

main.cpp:3:25: fatal error: http_socket.h: No such file or directory compilation terminated.

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main.cpp

#include "http_socket.h"

int main() { return 0; }

http_socket.cpp

#include "http_socket.h"
#include <string>

using namespace std;

http_responce::http_responce(string status_Code, string date, string server, string content_Type, string content_Length) {
Status_Code = status_Code;
Date = date;
Server = server;
Content_Type = content_Type;
Content_Length = content_Length;
}

http_socket.h

#ifndef HTTP_SOCKET_H
#define HTTP_SOCKET_H

#include <string>

using namespace std;

class http_responce 
{
    public:
    string Status_Code;
    string Date;
    string Server;
    string Content_Type;
    string Content_Length;

    http_responce(string status_Code, string date, string server, string content_Type, string content_Length);

    private:

    protected:
};

#endif

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Addition note:

I am very new to this language and accustomed to using an IDE, so please forgive me if it is something very trivial that I have missed.

Answer 1

Just as you are telling g++ where to find the http_socket.o object file, you need to help it out and tell it where it can find the http_socket.h header file you are including from main.cpp. You do this by passing the -I preprocessor option to g++ with the directory that contains http_socket.h.

Assuming http_socket.h is in the same folder as http_socket.o, you would use -I ~/src/c++/web so that your full command line for building webserver would be the following:

g++ -I ~/src/c++/web -o webserver ~/src/c++/web/http_socket.o -std=c++0x main.cpp

From the GCC documentation:

-I dir

Add the directory dir to the list of directories to be searched for header files. Directories named by -I are searched before the standard system include directories. If the directory dir is a standard system include directory, the option is ignored to ensure that the default search order for system directories and the special treatment of system headers are not defeated . If dir begins with =, then the = will be replaced by the sysroot prefix; see --sysroot and -isysroot.