从文本文件获取说明

Question

I have a homework. I have to create a hash table and use linked list to solve colissions. The hashtable is working quite good. Part of the asignment is reading a file and parse the contents to get instruccions.

The file contents:

Load("Via Lactea", "Galaxia")

Load("Galaxia", "Sistema Solar", "Sol")

Load("Via Lactea", "Hoyo negro", "001")

Find("Via Lactea","Luna")

Delete("Via Lactea","Jupiter")

Show()

My question what's the best (and easiest) way to create a C/C++ program to read the file contents and parse the instructions to operate my program. I'm new to C/C++ so i'm not sure what's the best way to solve this.

How can i read one line and know what kind of instruction is?

I would like to know some ideas

(My hashtable code is here http://pastebin.com/yVEeqvzG )

Answer 1

Since the main goal of your assignment is the hashtable part, you might want to make a quick-and-dirty hack that parses your file, just so you can start with the main part quickly.

The following is written in C though it will wirk in C++ too.

char line[100], command[100], word1[100], word2[100], word3[100];
FILE* f = fopen("whatever", "rt");

while (fgets(line, sizeof(line), f)) // read one line of text from file
{
    // The following is a format string for scanf.
    // It matches an opening quote, some text, and a closing quote.
    #define WORD "\"%[^\"]\""

    // Try to parse the line of text, applying all possible patterns.
    if (sscanf(line, "Load("WORD", "WORD", "WORD")\n", word1, word2, word3) == 3)
    {
        ...
    }
    else if (sscanf(line, "Load("WORD", "WORD")\n", word1, word2) == 2)
    {
        ...
    }
    else if (sscanf(line, "Find("WORD", "WORD")\n", word1, word2) == 2)
    {
        ...
    }
    else if (strcmp(line, "Show()\n") == 0)
    {
        ...
    }
}

Obligatory note: this usage of sscanf has security holes though you probably don't care about it.

Answer 2

This basic snippet is able to load the file line by line. How to manage the parsing is your duty, I would go with strtok_s but you will have to care about trimming space, checking for right amount of parameters, extract double quotes from strings and whatever.

#include <iostream>
#include <fstream>
using namespace std;

int main () {
  filebuf fb;
  fb.open("data.txt",ios::in);
  istream is(&fb);
  char buffer[256];

  while ((is.rdstate() & ifstream::eofbit) == 0) {
    is.getline(buffer,256);

    // handle your parsing here
  }

  fb.close();
  return 0;
}