Trouble With Input From a File

[kingcrim05]

I'm getting the same very large number for item and for each element in the array after that for loop is done. Why am i not pulling the 6 numbers from my input file? Thanks.

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

int main(int argc, char *argv[])
{
	/* Extract value for # of elements in array */
	int i;
	sscanf (argv[2], "%d", &i);	
	// printf("i is %d\n", i);
	
	/* Create Input and Output Streams */
	ifstream fin;
	ofstream fout;

	/* Oprn Input and Output Streams */
	fin.open("numlist.dat");
	fout.open("numlist.dat");

	/* Tests to ensure files opened */
	if(fin.fail())
	{
		cerr << "Input did not open\n";
		exit(2);
	}
	if(fout.fail())
	{
		cerr << "Output file did not open\n";
		exit(2);
	}

	 /* Construct New Array */
	float *floatArray= new float[i];

	/* Put numbers from list into array */
	float item;
	int j=0;
	// printf("Put Numbers from list into array\n"); 
	for (j=0; j<i;j++)
	{	
		fin >> item;
		printf("item is %f\n", item);
		floatArray[j]=item;
		printf("floatArray[%d] is %f\n", j, floatArray[j]);
	}
	getchar();
}

[Ancient Dragon]

If you only enter one argument then argv[2] is invalid. The program will only have argv[0] and argv[1].

[kingcrim05]

There will always be exactly two arguments that are put in on the command line. The first is the name of the input file (which will also be the output file once renamed) and the second is a # that is the # of floats in the input file to be read.

[Dave Sinkula]

fin.open("numlist.dat");
	fout.open("numlist.dat");

Perhaps first open for input. Then after you've extraced what you want and closed the file, then open the same file for output.

[kingcrim05]

Nope, i'm still getting -107374176.000000 for all items

[Dave Sinkula]

Just sayin'.

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

int main(int argc, char *argv[])
{
	/* Extract value for # of elements in array */
	int i;
	sscanf (argv[2], "%d", &i);
	// printf("i is %d\n", i);

	/* Create Input and Output Streams */
	ifstream fin;
	ofstream fout;

	/* Oprn Input and Output Streams */
	fin.open("numlist.dat");
	//fout.open("numlist.dat");

	/* Tests to ensure files opened */
	if(fin.fail())
	{
		cerr << "Input did not open\n";
		exit(2);
	}
	if(fout.fail())
	{
		cerr << "Output file did not open\n";
		exit(2);
	}

	 /* Construct New Array */
	float *floatArray= new float[i];

	/* Put numbers from list into array */
	float item;
	int j=0;
	// printf("Put Numbers from list into array\n");
	for (j=0; j<i;j++)
	{
		fin >> item;
		printf("item is %f\n", item);
		floatArray[j]=item;
		printf("floatArray[%d] is %f\n", j, floatArray[j]);
	}
}

/* numlist.dat
10 20 30 40 50
*/

/* my output
Debug\cpp.exe file.txt 5
item is 10.000000
floatArray[0] is 10.000000
item is 20.000000
floatArray[1] is 20.000000
item is 30.000000
floatArray[2] is 30.000000
item is 40.000000
floatArray[3] is 40.000000
item is 50.000000
floatArray[4] is 50.000000
*/

[kingcrim05]

I'm confused why it would be working for you and not for me then. I'm using Visual Studio 2008 for the first time here so that may be it. Where should i be storing my numlist.dat? i have in my source folder along with my msort.cpp file. Is that the problem?

[Ancient Dragon]

It doesn't work for you because when you open the file for output ofstream truncates it to zero length, erasing all its contents. Comment out ofstream and its open statement then your program will work (after you add the data back into the file again).