C - programming a makefile and how they work - c

Question

So given three files:
main.h
#include <stdio.h>
void printFunc(*char);
main.c
#include "main.h"
int main(){
printFunc("Hello World\n");
return 0;
}
printFunc.c
#include "main.h"
void printFunc(char *string){
printf("%s", string);
return;
}
You can compile using gcc on a linux machine as follows:
gcc -g -Wall -c file1.c //compile but do not link file
gcc -g -Wall -c file2.c //same
gcc file1.o file2.o -o main //executable "main"
or
gcc -g -Wall file1.c file2.c -o main
But I am concerned with how the header file gets included. I came across this when I was working on creating a "makefile" when I noticed that some tutorials will do something like this:
main : main.o printFunc.o
gcc -o main main.o printFunc.o
main.o : main.c
gcc -g -Wall -c -o main.o main.c
printFunc.o : printFunc.c
gcc -g -Wall -c -o printFunc.o printFunc.c
and others will include the header file as a dependent with:
main : main.o printFunc.o //main.h EDIT
//commands
main.o : printFunc.o main.h
//commands
Finally:
So, is it necessary to include the header file as a dependent to the executable? When does the include file get placed within the sources?
And also one could use this command:
executableName : dependencies.o //and a header file?
gcc -g -Wall -o executableSource.c
Which could be done with the line:
gcc -g -Wall -o executableName executableSource.c
Will the second command be run but the first is shorthand notation?
And finally, I thought the "-o" command was "send output to", if you will. If that way, it seems intuitive to run the command like:
gcc compileThisFile andSendOutputTo thisExecutableFile
gcc someSource.c -o executableFile
But with the notation listed above its more like:
gcc sendOutputTo thisExecutableFile fromThisSource
Is that correct?

Answer 1

main : main.o printFun.o main.h is definitely wrong. That's saying that the header is a prerequisite for linking. A header is a prerequisite for compilation.
Assuming what you really meant was to specify the header as a compilation dependency (e.g. printFunc.o : printFunc.c printFunc.h), this means that if the header changes, the object file will be automatically regenerated. If you don't, then it won't.

Answer 2

A dependency in Makefile is saying that whenever any of the listed files change, run the command again. It does not mean that the listed file will be included into the compilation or linking. You still need the regular #include "main.h" in your sources.
Thus, this works too:
printFunc.o : printFunc.c someReadmeFile.txt
gcc -g -Wall -c -o printFunc.o printFunc.c
Whenever printFunc.c or someReadmeFile.txt is updated, gcc -g -Wall .... will be executed again.
I hope it's clearer now.