Switches

[cpq2g1zw2]

I don't know what happened to my last post, but no matter. I figured out how to add command line switches.

So below is the program I have been working on today Just practicing.

My question is how do I run the write function by default with no command line parameters, but NOT run if I do supply parameters.

I tried simply removing

if ((argc >= 2 ) && ( strcmp(argv[1], "-w") == 0))

But if I do that, the write function runs even if I supply command line parameters. And if I simply remove the '-w' to leave a blank "", then it wont run at all.

#include <iostream>
#include <string>
#include <cstring>
#include <fstream>
int main(int argc, char* argv[])
{

if ((argc >= 2 ) && ( strcmp(argv[1], "-w") == 0))
	{

	char choice;
do {

	std::string test;
	std::cout << "Enter a string: ";
	getline (std::cin, test);
	
	std::ofstream outfile;
	outfile.open("test.txt", std::ios_base::app);
	if (outfile.is_open()) {
	outfile << test << '\n'; 
}
	else std::cout << "Unable to open file";


do {
	std::cout << "Would you like to enter another string? ";
	std::cin >> choice;
	std::cin.clear();
	std::cin.ignore(1000, '\n');

	if (choice != 'y' && choice !='n')
	std::cout << "You did not make a valid selection" << '\n';
}
	while (choice != 'y' && choice !='n');
	
}
	while (choice == 'y');
	
	if (choice !='y' && choice !='n')
	return 0;
}
	if ((argc >= 2 ) && ( strcmp(argv[1], "-v") == 0))
	{
	std::string line;
	std::ifstream myfile ("test.txt");
  
	if (myfile.is_open())
	{
	while ( getline (myfile,line) )
	{
	std::cout << line << '\n';
	}
	myfile.close();
	}

	else std::cout << "Unable to open file";}

	

	else if ((argc >= 2 ) && ( strcmp(argv[1], "-e") == 0))


	{

char erase;

	std::cout << "This will erase contents of file. Proceed? ";
	std::cin >> erase;

	if (erase !='y')
	return 0;

        std::ofstream myfile;
	myfile.open ("test.txt");
	myfile << "";
	myfile.close();
	

	std::cout << "Contents of file were erased" << '\n';
}


}

[ShiftLeft]

int main(int argc, char* argv[]) {
	
	if ( argc == 2) {
		char *choice = argv[1];
		
		switch ( choice[1] ) {
			case 'w':
				break;
			case 'v':
				break;
			case 'e':
				break;
			default:
				break;
		}
	}
	else {
		// Erase or write function goes here.
	}
	
	return 0;
}

[cpq2g1zw2]

default , in this example, is only being executed if one supplies improper command line switch, not by default (by simply running the program with no parameters), Which was my whole problem.

[ShiftLeft]

Incorrect, if you don't supply any parameters argc won't equal 2. Default is only there is you enter something other than w-v-e.

[TheIdeasMan]

if (argc == 0) {
  // run function
}

// do something else 

ShiftLeft's implementation is a good idea for processing arguments, do loops are a bit messy IMO.

Good Luck !!

[cpq2g1zw2]

Thank you both for your feedback. I will work on it!

*edit* TheIdeasMan, it's still not working.

Since you both think switch would be better, I am certainly willing to rework my program, but I still have the problem of not being able to run the program without parameters.

[cpq2g1zw2]

Don't worry...I don't expect you guys to figure it all out for me. I will continue to reasearch and see what I can come up with :-)

[ShiftLeft]

Keep in mind, my example has one drawback that if you enter more than 1 argument in command line, it will also execute write.

int main(int argc, char* argv[]) {
	
	if ( argc == 2) {
		char *choice = argv[1];
		
		switch ( choice[1] ) {
			case 'w':
				break;
			case 'v':
				break;
			case 'e':
				break;
			default:
				break;
		}
	}
	else if ( argc == 1 ) {
		// Erase or write function goes here.
	    }
	else
		cout << "Too many arguments" << endl;
		
	return 0;
}

or

#include	<iostream>

using namespace std;

int main(int argc, char* argv[]) {
	char *choice = argv[1];
	
	switch ( argc ) {
		case 2:
			cout << "Processing " << choice << endl;
			
			switch ( choice[1] ) {
				case 'w':
					break;
				case 'v':
					break;
				case 'e':
					break;
				default:
					break;
			}
			break;
		
		case 1:
			// Implement erase/write code here
			break;
			
		default:
			cout << "Too many arguments" << endl;
	}
	
	return 0;
}

Might be a better alternative.

[cpq2g1zw2]

Thank you ShiftLeft. I love learning, so the new ideas are great! I appreciate it :-)

[ShiftLeft]

My question is how do I run the write function by default with no command line parameters, but NOT run if I do supply parameters.

But I still have the problem of not being able to run the program without parameters.

You'll have to be more specific what you mean as these statements are ambiguous. If you mean you want to execute write in any case then you just need to put a call to that function in line 22 of last example.

[cpq2g1zw2]

Sorry ShiftLeft. I am a brand-newbie. I am taking a course in C++ and haven't even gotten to arrays yet!
I just wanted to venture off and learn some things for practicing reading from and writing to text files.

Anyways, just found a code snippet that works for what I wanted

if ( argc != 2 ) // argc should be 2 for correct execution
std::// We print argv[0] assuming it is the program name
cout<<"usage: "<< argv[0] <<" <filename>\n";

[cpq2g1zw2]

if (argc !=2){
std::cout << "No arguments" << '\n';
}

Finally got it working the way I want! Thank you guys for your help. :-)

[cpq2g1zw2]

if (argc !=2){
std::cout << "Usage:" << '\n';
std::cout << "-w to write to file" << '\n';
std::cout << "-v to verify contents of file" << '\n';
std::cout << "-e to erase contents of file" << '\n';
}

This is what I was trying to do. I wanted to display usage if no command line arguments were used and didn't want it to display if command line arguments *were* used.

I guess I didn't ask my question very well.

God, it seems so obvious now. LOL!