C++ Execute a function through cmd or shell - c++

Question

First thing,sorry my bad english and any mistakes in asking.
I've searched it a lot,but i was not able to explain in simple words.
I work with Linux servers and command line, i'm used to calling programs through it like
./program foo -u adm -p 123
But i always wondered how make programs to act like that,i mean call a specific function and write parameters without needing to open program itself.
In other words.
If i code a C++ like that,and compile
#include <iostream>
using namespace std;
void SayHello(string Name)
{
cout << " Hello " << Name;
}
how can i call it through the command line like
./Program SayHello CARLOS
Sorry about my ignorance,but it's something that i want to learn.
Thanks for your attention

Answer 1

If you want to call a function of your program based on the arguments, you could do something like:
int main(int argc, char* argv[]) {
if(argc > 2){
if(strcmp(argv[1], "SayHello") == 0){
SayHello(argv[2]);
}
}
return 0;
}
Of course this is just a sketch and i can be improved if what you want to achieve is more complex.
You could also build a more dynamic solution if you want other functions than the "SayHello" one to be callable too.

Answer 2

int main( int argc, char** argv )
Here argc refers to the number of argument (arg count)
argv refers to the argument array ("char*" array) (arg value)
Calling your program from command line will result in a main entry with these parameters ; it remains to parse them and launch the command accordingly.

Answer 3

void main() {
char *name[] = {
"./program",
"-c",
"foo -u adm -p 123",
NULL
};
execvp(name[0], name);
}

Answer 4

There you go every executable needs a main function which is the entry point for execution.
#include <iostream>
#include <string>
using namespace std;
void SayHello(string Name)
{
cout << " Hello " << Name;
}
int main(int argc, char* argv[])
{
if (argc > 1)
SayHello(argv[1]);
}
To compile this do
$g++ hello.cpp
It should produce a.out on Linux.
To run it
./a.out "World!"