What is ld returned exit status 1?

Question

The following is the code I've written in an implementation file for a function that calculates median of a double vector :

#include<algorithm>
#include<stdexcept>
#include<vector>
#include "median.h"
using std::domain_error;
using std::vector;

double median(vector<double> vect)
{
    typedef vector<double>::size_type vec_sz;
    vec_sz size=vect.size();
    if(size==0)
        throw domain_error("median of an empty vector");
    sort(vect.begin(),vect.end());
    vec_sz mid= size/2;
    return size%2==0 ? (vect[mid]+vect[mid-1])/2 : vect[mid];
}

I get the following when I compile it using g++ median.cpp on the command line:

/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/Scrt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status

It's the error you posted: *undefined reference to main*. You don't have a `main` function. — chris, Jan 05 '18 at 03:39
Please show the command line you used to compile and link your program. — jww, Jan 05 '18 at 03:40
@chris I saw this from Accelerated C++ and there is no main function inclusion in their program — lakshay.angrish, Jan 05 '18 at 03:41
Possible duplicate of [What is an undefined reference/unresolved external symbol error and how do I fix it?](https://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix) — Ken White, Jan 05 '18 at 03:42
@lakshay.angrish, Then it's presumably meant to be compiled separately and linked with something else that does have a `main` function. The book should go over how to build its code. — chris, Jan 05 '18 at 03:47
@chris The book says that by defining functions in seperate files, we can compile the functions seperately and before our main program. And, I actually tried to include this function implementation's header file in a test program with a main function, but that still gives the same error. — lakshay.angrish, Jan 05 '18 at 03:51
Possible duplicate of [How do I link object files in C? Fails with "Undefined symbols for architecture x86\_64"](https://stackoverflow.com/questions/15441877/how-do-i-link-object-files-in-c-fails-with-undefined-symbols-for-architecture) — jww, Jan 05 '18 at 04:05

score 0 · Answer 1 · answered Jan 05 '18 at 04:07

The error is because you don't have a main function. Create a main function and call the median function from main function.

#include<algorithm>
#include<stdexcept>
#include<vector>
#include "median.h"
using std::domain_error;
using std::vector;

double median(vector<double> vect)
{
    typedef vector<double>::size_type vec_sz;
    vec_sz size=vect.size();
    if(size==0)
        throw domain_error("median of an empty vector");
    sort(vect.begin(),vect.end());
    vec_sz mid= size/2;
    return size%2==0 ? (vect[mid]+vect[mid-1])/2 : vect[mid];
}

void main()
{
   // call the median(vector<double> vect) function from here
    vector<double> vect = {10,20,30}; // initialize with numbers 
    double retval = median(vect);
}

What is ld returned exit status 1?

1 Answers1