Using getline to read in data

krisbot · #1 24-Oct-2004, 01:08

Hi, I've read these forums for help a lot of times, but this is my first time posting . Anyways, I'm looking for help on a problem I'm having reading in and storing data. The program is designed to read data in from a file, store the information for later calculations, and then save the data to an outfile. The data is information from the 2000 Presidential election, here is an example:

State Elec Vote Gore Bush Nader Buchanan
Alabama 9 695602 944409 18349 6364
Alaska 3 79004 167398 28747 5192

Opening the file and saving the data to a file is simple enough for me, but I'm perplexed on how to read the data in, and what variables to store it under. I've tried using the getline function in a while loop, but I can never figure the syntax out, and I just end up getting frustrated. Also, I'm confused on how to avoid storing the first line into the variables (State Elec Vote Gore Bush Nader Buchanan), so they won't get full of a bunch of char value garbage. If anyone could show me an example of how this data could be read in a stored, I'd be most appreciative. Thanks again.

dsmith · #2 24-Oct-2004, 07:45

Hello krisbot. Long time listener, first time caller huh? Welcome to GIDForums.

I know that your original question was about getline. I don't know if you were intent on using getline, but I had to answer this anyway. Throughout this forum, scanf has a pretty bad reputation (with reason), but this program is perfect for scanf (IMHO).

Anyway, I whipped this up real quick to show how this can be used:

CPP / C++ / C Code:

#include <stdio.h>

struct{
	char	state[30];
	int		electoral;
	long	gore;
	long	bush;
	long	nader;
	long	buchanan;
}vote[50];


int main(int argc, char* argv[])
{
	
	FILE* 	fp;
	int		loop;
	char	junk[80];
	
	if(argc!=2)
		printf("You must specify a file to read.\n");
	else{
		if( (fp=fopen(argv[1],"r") ) == NULL)
			printf("Could not open file: %s\n",argv[1]);
		else{
			fgets(junk,80,fp);			//Ignore first line.
			loop = 0;
			while(!feof(fp)){
				fscanf(fp,"%s %d %ld %ld %ld %ld",
							vote[loop].state,
							&(vote[loop].electoral),
							&(vote[loop].gore),
							&(vote[loop].bush),
							&(vote[loop].nader),
							&(vote[loop].buchanan) );
				loop++;
			}
			vote[loop].state[0] = (char)0;
			fclose(fp);
			printf("\nVoting\n");
			printf("State\tElectorals\tGore\tBush\tNader\tBuchanan\n");
			printf("-----\t----------\t----\t----\t-----\t--------\n");
			loop = 0;
			while( (loop<50) && (vote[loop].state[0]) ){
				printf("%s\t%d\t\t%ld\t%ld\t%ld\t%ld\n",
							vote[loop].state,
							vote[loop].electoral,
							vote[loop].gore,
							vote[loop].bush,
							vote[loop].nader,
							vote[loop].buchanan );
				loop++;
			}
			
		}
	}
	
	return 0;
}

It's not very fancy and it is entirely static in storage. Notice that I just read and throw away the first line since I know what the catagories are...

My apologies if scanf is not what you want to use, but it is very good at reading structured data like this.

Good luck!

WaltP · #3 24-Oct-2004, 11:30

Quote:

Originally Posted by dsmith

I know that your original question was about getline. I don't know if you were intent on using getline, but I had to answer this anyway. Throughout this forum, scanf has a pretty bad reputation (with reason), but this program is perfect for scanf (IMHO).

Actually, IMAO

scanf() has a bad reputation on pretty much ALL forums. That's because it's very difficult to control the input. And scanf() leaves junk in the input stream that messes up future reads. But fscanf() is a slightly different matter since you know (or should know) the format of the data at all reads.

But to be completely safe, change all fscanf()'s to

CPP / C++ / C Code:

      fgets(junk,80,fp);      //read a full line.
      sscanf(junk,"%s %d %ld %ld %ld %ld",
              vote[loop].state,
              &(vote[loop].electoral),
              &(vote[loop].gore),
              &(vote[loop].bush),
              &(vote[loop].nader),
              &(vote[loop].buchanan) );

This way you won't have to deal with any input issues dealing with extra characters left in the file like scanf() does with the input stream.

krisbot · #4 24-Oct-2004, 13:49

Quote:

Originally Posted by dsmith

Hello krisbot. Long time listener, first time caller huh? Welcome to GIDForums.

I know that your original question was about getline. I don't know if you were intent on using getline, but I had to answer this anyway. Throughout this forum, scanf has a pretty bad reputation (with reason), but this program is perfect for scanf (IMHO).

Anyway, I whipped this up real quick to show how this can be used:

CPP / C++ / C Code:

#include <stdio.h>

struct{
	char	state[30];
	int		electoral;
	long	gore;
	long	bush;
	long	nader;
	long	buchanan;
}vote[50];


int main(int argc, char* argv[])
{
	
	FILE* 	fp;
	int		loop;
	char	junk[80];
	
	if(argc!=2)
		printf("You must specify a file to read.\n");
	else{
		if( (fp=fopen(argv[1],"r") ) == NULL)
			printf("Could not open file: %s\n",argv[1]);
		else{
			fgets(junk,80,fp);			//Ignore first line.
			loop = 0;
			while(!feof(fp)){
				fscanf(fp,"%s %d %ld %ld %ld %ld",
							vote[loop].state,
							&(vote[loop].electoral),
							&(vote[loop].gore),
							&(vote[loop].bush),
							&(vote[loop].nader),
							&(vote[loop].buchanan) );
				loop++;
			}
			vote[loop].state[0] = (char)0;
			fclose(fp);
			printf("\nVoting\n");
			printf("State\tElectorals\tGore\tBush\tNader\tBuchanan\n");
			printf("-----\t----------\t----\t----\t-----\t--------\n");
			loop = 0;
			while( (loop<50) && (vote[loop].state[0]) ){
				printf("%s\t%d\t\t%ld\t%ld\t%ld\t%ld\n",
							vote[loop].state,
							vote[loop].electoral,
							vote[loop].gore,
							vote[loop].bush,
							vote[loop].nader,
							vote[loop].buchanan );
				loop++;
			}
			
		}
	}
	
	return 0;
}

It's not very fancy and it is entirely static in storage. Notice that I just read and throw away the first line since I know what the catagories are...

My apologies if scanf is not what you want to use, but it is very good at reading structured data like this.

Good luck!

What compiler is used for that code? I use Microsoft Visual Studio C++ Pro (got it for free). Here is an example of what my code generally looks like:

CPP / C++ / C Code:

#include<iostream>
#include<fstream>
#include<string>

using namespace std;

int main()
{	
	ifstream inFile;

	inFile.open("election.txt");

	if(!inFile) //Checking for inFile
	{
		cout << "File not found." << endl;
	}

	inFile.close();

	return 0;
}

That was just opening an infile and checking to see if it is there (for me anyways). I don't know if its just a different compiler or if I haven't got to that lvl of coding yet.

dsmith · #5 24-Oct-2004, 16:57

Hi Krisbot. That is an ancient language known as "C"

It should compile on any about any C compiler, there is nothing exotic there at all.

As a personal preference, I like the stdio input/output much better than iostream & fstream. It is probably what I am used to, but to me, it is much easier to use.

That is why I put the comment about your possible attachment to getline before I posted the code. Anyway, I think this is a great illustration of the ease of use of the fscanf function. Perhaps someone that is more fond of the fstream library will post an alternate solution using that.

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