Unable to compile Hello World

Question

Sorry if this is a repeat question, but I couldn't find an answer that worked.

I'm writing a Hello World C program for the first time in a long time. I'm fairly certain the code is right, but it won't compile.

Running MAC OS 10.13.6 and I just downloaded XCode last week. The program compiles into an object file using

cc -c test.c -o test.o

without a problem. However, I can't create an executable using

cc test.o -o test

Here's the code:

#include <stdio.h>
int Main()
{
    printf("Hello World");
    return 0;
}

When I go to create the executable, I get

Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64

I'm guessing I need to add some compiler flags but can't figure out which ones.

`int Main()` this is not how you write a main function in C. — tkausl, Jan 20 '19 at 15:38
Names in C are case sensitive, and the entry point function needs to be named "main", not "Main". — John Bollinger, Jan 20 '19 at 15:38
And when `main()` takes no parameters it is `int main(void)`. — Swordfish, Jan 20 '19 at 16:24
Apart from the multiple comments above which tell you how to fix. I would bet that your build tools also told you so. Could you show the verbatim full error message you got? a) The one you got. b) The one you get when you use strict warnings and a nitpicking configuration of build tools. Start with `-Wall`. — Yunnosch, Jan 20 '19 at 16:28
See it tells you that it is looking for something called "main" not "Main". Even though the "_" might be confusing, this should have made you aware of the capitalisation mistake. Reading error messages really is the best first level of help with anything that does not build. — Yunnosch, Jan 20 '19 at 16:30
@alk People tend to confuse beginner mistakes with bad questions. — Yunnosch, Jan 20 '19 at 16:34

score 5 · Accepted Answer · edited Jan 20 '19 at 16:38

It sounds like you are just starting out in your journey into c code. This is a great opportunity to learn about c, compiling, and linking.

What you have written can compile just fine into an object file (containing a function called Main()). However, to link into an executable that can run from your OS, you need to define an entry point which is assumed to be a function called main (case sensitive as John mentioned above).

Check out this resource: http://www.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html for an explanation of what the gcc compiler gets up to behind the scenes.

You just need to make a couple of small changes to get your code to work as expected:

#include <stdio.h>

int main(void) {
    printf("Hello, world!\n");
    return 0;
}

Main needs to be lowercase main.
While int main() will work, int main(void) is technically more accurate (see void main(void) vs main())
You probably want a line new line after Hello, world!, so add the \n. (https://www.tutorialspoint.com/c_standard_library/c_function_printf.htm)

Unable to compile Hello World

1 Answers1