Huffman

[thanhquan1704]

My code is

#include <iostream>
#include <map>
#include <fstream>
struct huffman_node {
	int priority;
	char letter = 0; // Use null char for internal nodes,
	// and the actual char for leaf nodes
	huffman_node* left = nullptr, * right = nullptr;
};
void freq_dist_from_file(std::map<char, int>&, std::ifstream&)
{
	std::ifstream my_file("text.txt");
	if (!my_file.is_open())
		throw std::runtime_error("Can not open file.");
	std::map<char, int> freq_dist;
	freq_dist_from_file(freq_dist, my_file);
}
int main()
{
	system("pause");
}

What should I write on main to check that my text.txt file open suceessful or not?

[nuderobmonkey]

In my opinion, it would be better, opening the file in main() and testing it there for successfully opening. Also, I think it isn't a good idea calling your freq_dist_from_file() in a recursive manner if you don't want to risk a stack overflow.

[thanhquan1704]

It is a structure that my professor gives me so I need to follow it.
So how can I check that my text.txt file open suceessful or not?

[nuderobmonkey]

Are you sure that your professor told you, recursively invoking the function? I could bet, your prof was providing this code for analyzing and recognizing what's wrong with.

But anyway, a possibility to check if your file would be correctly opened in main would be, catching the exception.

    bool error_happened = false;
    try { freq_dist_from_file( /* ... */ ); }
    catch ( std::runtime_error & e ) {
        std::cerr << e.what() << '\n';
        error_happened = true
    }

	system("pause");
	if ( error_happened ) exit( EXIT_FAILURE );
	exit( EXIT_SUCCESS );

[thanhquan1704]

It still not work. Can you please give me a full code?

[Thomas1965]

void freq_dist_from_file(std::map<char, int>&, std::ifstream&)
Seems more that you have to create the map and the stream in main and pass it to void freq_dist_from_file.
To do it you need to give the parameters a name.
What is the huffman_node needed for if you use a map?

Can you please give me a full code?

We are not a code writing service.
What would you learn from it?

[nuderobmonkey]

We are not your nannies. Post your code that you have so far elaborated, together with the error messages of your compiler.

[thanhquan1704]

#include <iostream>
#include <map>
#include <fstream>
struct huffman_node {
	int priority;
	char letter = 0; // Use null char for internal nodes,
	// and the actual char for leaf nodes
	huffman_node* left = nullptr, * right = nullptr;
};
void freq_dist_from_file(std::map<char, int>&, std::ifstream&)
{
	std::ifstream my_file("text.txt");
	if (!my_file.is_open())
		throw std::runtime_error("Can not open file.");
	std::map<char, int> freq_dist;
	freq_dist_from_file(freq_dist, my_file);
	bool error_happened = false;
	try 
	{ 
		freq_dist_from_file(freq_dist, my_file); 
	}
	catch (std::runtime_error & e) 
	{
		std::cerr << e.what() << '\n';
		error_happened = true;
	}
	if (error_happened) 
		exit(EXIT_FAILURE);
	exit(EXIT_SUCCESS);
}
int main()
{
	std::map<char, int> letter;
	std::ifstream inputdata;
	inputdata.open("text.txt");
	freq_dist_from_file(letter,inputdata);
	system("pause");

my error is "a reference of type cannot be initialized with a value of std::fstream"

[kbw]

There are a number of problems.

freq_dist_from_file() is recursive, but you don't pass thru the map, you create a local one and trash the results after each return.

You shouldn't be handling the exception in freq_dist_from_file(). That's the magic of exceptions, you throw the error in one function and you can catch them anywhere down the call stack. In this case, main() should catch error, freq_dist_from_file() should just throw it.

Finally, you're not actually doing anything useful, but if the exercise is to learn about exceptions, that's ok.