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Input files with multiple columns

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Join Date: Oct 2009

Posts: 14

Reputation: NICEGUY123 is an unknown quantity at this point

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NICEGUY123 NICEGUY123 is offline

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Input files with multiple columns

Oct 17th, 2009

I need some help, fairly new to C++ and I know a little about C. What i am trying to do is get a txt file that looks like this

4 //first number tells how many rows are coming next.
3 54
2 51
9 32
2 34

what i want to do is get the numbers into a array so that i can use them later on in a function. Here is what i wrote so far, and is there a better way in C++.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
 
# include <stdio.h>
 
 
void READFile(char* filename)
{
	int num;
 
 
 
FILE* inputfile;
if ((inputfile = fopen(filename, "r")) ==NULL)
{
printf("file not found, unable to open\n");
 
}
 
	fscanf( inputfile, "%d", num);
 
	int color[num];
	int value[num];
 
	for (int i = 0; i< num; i++);
	{
		fscanf(inputfile, "%d","%d",  &color, &value);
	}
 
 
}
# include <stdio.h>


void READFile(char* filename)
{
	int num;
	
	

FILE* inputfile;
if ((inputfile = fopen(filename, "r")) ==NULL)
{
printf("file not found, unable to open\n");

}

	fscanf( inputfile, "%d", num);
	
	int color[num];
	int value[num];
	
	for (int i = 0; i< num; i++);
	{
		fscanf(inputfile, "%d","%d",  &color, &value);
	}

	
}

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Join Date: Aug 2007

Posts: 1,675

Reputation: vmanes is a splendid one to behold

Solved Threads: 193

vmanes

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Posting Virtuoso

Oct 18th, 2009

Here's your code, translated in to C++.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <fstream>
#include <iostream>
using namespace std;
 
 
void READFile(char* filename)
{
	int num;
 
	int color[100];  //make this large enough for any problem set
	int value[100];
 
	ifstream inputfile;
 
	inputfile.open( filename );
	if ( !inputfile )
	{
		cout << "file not found, unable to open\n";
		return;  //added
	}
 
	inputfile >> num ;
 
/*
	int color[num];  //oops, not yet legal in C++
	int value[num];  //although array declaration with variables
			//is supported in some compilers
*/
	for (int i = 0; i < num; i++);
	{
		inputfile >> color[i] >> value[i];
	}
}
#include <fstream>
#include <iostream>
using namespace std;


void READFile(char* filename)
{
	int num;

	int color[100];  //make this large enough for any problem set
	int value[100];

	ifstream inputfile;

	inputfile.open( filename );
	if ( !inputfile )
	{
		cout << "file not found, unable to open\n";
		return;  //added
	}

	inputfile >> num ;

/*
	int color[num];  //oops, not yet legal in C++
	int value[num];  //although array declaration with variables
			//is supported in some compilers
*/
	for (int i = 0; i < num; i++);
	{
		inputfile >> color[i] >> value[i];
	}
}

Note that by declaring the color and value arrays in the function, they only exist in that function. Perhaps they should be declared in main( ) and passed to the function?

I don't think your C input was quite correct, you input to the address of the array, but never incremented to fill other array elements. Should that have been

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
fscanf(inputfile, "%d","%d",  &color[i], &value[i]);
fscanf(inputfile, "%d","%d",  &color[i], &value[i]);

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