Compiled archive with ar, compiles manually, ld does not find

Question

I have compiled a hello world library to test my build setup:

// hw.cpp
#include<iostream>
#include"hw.h"

void hw(){ std::cout << "hw"<<std::endl; }

// hw.h
void hw();

// main.cpp
#include"hw.h"
int main(int argv, char ** argc){
  hw();
  return 0;
}

// BUILD COMMAND (ommitting proj directories, replacing with '.')
g++ -I. -o hw.o hw.cpp

// Archive Command
ar -rcs hw.a hw.o

// Compile (works as expected)
g++ -I. -o hw main.cpp hw.a

// Compile with ld
g++ -I. -L. -o hw main.cpp -lhw

And the result is failure. I have tried absolute paths, looked at ld documentation; and in general burnt time trying to figure out this issue.

What could be going on here?

Exact error code:

/usr/bin/ld: cannot find -lhw
collect2: error: ld returned 1 exit status

Answer 1

I'm guessing your error message, but after trying your code myself, I think that your problem is that ld cannot find your library. Libraries have to be named with the prefix lib. Rename hw.a to libhw.a and it should work.