compile and run c++ program with own header files in linux

Question

This is my first go at making my own header file. I am trying to make a simple Hello World program in C++ on Ubuntu. made 3 files as follows :

//hello.h file

#ifndef HELLO_H
#define HELLO_H

//my own code

void hello();

#endif

//hello.cpp file

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

using namespace std;

void hello()
{
    cout << "This line is printed from header.";
}

//main.cpp file

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

using namespace std;

int main()
{
    cout << "in main" << endl << endl;
    hello();
    return 0;
}

I've tried

g++ -I /home/Desktop/hello/ -c hello.cpp -o hello.o

to compile header file and this command worked.

then, while doing

g++ -o main main.cpp

I am ending up with following error:

/tmp/ccb0DwHP.o: In function `main':
main.cpp:(.text+0x2e): undefined reference to `hello()'
collect2: error: ld returned 1 exit status

Please suggest whether changes need to be made in any file or in any command in the terminal?

thank you

Options -c and -o together are not recommended (not to say prohibited). g++ warns of that. — Sandburg
– Sandburg, Commented Jan 18, 2019 at 22:09

ohmu · Accepted Answer · 2015-03-07 16:05:38Z

9

You don't link to hello.o in the command below:

g++ -o main main.cpp

Try this:

g++ -o main main.cpp hello.o

Or for such simple program, just issue the command below:

g++ -o main main.cpp hello.cpp

For ease of use, create a makefile, then you just run make:

make

A simple makefile:

helloprogram: hello.h hello.cpp main.cpp

    g++ -o helloprogram main.cpp hello.cpp

clean:

    rm helloprogram

edited Mar 7, 2015 at 16:05

ohmu

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answered Mar 6, 2015 at 5:57

Frank Zhang

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2 Comments

Sahil Arora Over a year ago

When we use iostream or something like that, we do not compile using g++ main.cpp iostream.cpp. Why does that work and not our program?

Sandburg Over a year ago

@SahilArora No, the standard library is a dependency : shared libraries, that means they are either header only or already compiled (.so).

Ningrong Ye · Accepted Answer · 2019-01-18 21:58:35Z

0

Put hello.h in Path2Hello;

g++ -o main -I Path2Hello main.cpp hello.cpp

ps: -I option to specify an alternate include directory (for header files).

answered Jan 18, 2019 at 21:58

Ningrong Ye

1,28712 silver badges10 bronze badges

Comments

jainath kumhar · Accepted Answer · 2021-01-17 14:37:20Z

-2

To compile and run a C language program, you need a C compiler. To setup a C language compiler in your Computer/laptop, there are two ways:

Download a full fledged IDE like Turbo C or Microsoft Visual C++, which comes along with a C language compiler. Or, you use any text editor to edit the program files and download the C compiler separately.

answered Jan 17, 2021 at 14:37

jainath kumhar

11 bronze badge

1 Comment

jainath kumhar Over a year ago

for more info refer to this link: studytonight.com/c/compile-and-run-c-program.php

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