Question

How do I use getline to read a file into an array?

Asked by: vwps

I am trying to read a file into a 2D integer grid array. When I run this code, I get two errors - one at each use of getline. The error is: "no matching function for call to 'getline[(((long unsigned int)(((int)rows) - 1)) + 1u)][(((long unsigned int)(((int)cols) - 1)) + 1u)], int, char)' ". Is something wrong with my input to getline or the integer array?

#include <iostream>
#include <fstream> 
using namespace std;
 
int main () 
{
	// open the file
	ifstream sampleGrid("/Users/vshen/Documents/EECS 311/Program 1/sample_grid.txt");
 
	if (sampleGrid)
	{
		cout << "File opened." << endl;
	}
 
	// exit the program if the file can't be opened
	if (!sampleGrid)
	{
		cerr << "File cannot be opened." << endl;
		exit (1);
	}
	
	// figure out the number of rows and columns... or just assume they're 10
	int rows = 10;
	int cols = 10;	
	// create the array that will store the grid
	int rowsread = 0;
	int colsread = 0;
	int myArr[rows][cols];
	
	while(!sampleGrid.eof())
	{
		getline(myArr, 20, '\t');
		if(rowsread == rows)
		{
			rowsread = 0;
			colsread++;
			getline(myArr, 20, '\t');
		}
		rows++;
	}
	return 0;
}

                                  
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Asked On
2009-04-18 at 19:26:51ID24334964
Tags

C++

,

getline

,

array

Topic

C++ Programming Language

Participating Experts
3
Points
500
Comments
5

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Answers

 

by: doraemon2555Posted on 2009-04-18 at 20:11:50ID: 24177792

With getline(), you try getting line from a file, the signature of the function will be:
getline(char**, size_t*, FILE*)
getdelim(char**, size_t*, int, FILE*)

Make sure your myArr is what you want to put (Do you want to dereference once first? It was a 2D array)
Check also the size you pass into the getline/getdelim will not overflow your char array...

 

by: ewest02Posted on 2009-04-18 at 20:20:55ID: 24177811

look at the definition of getline()

basic_istream& getline(char_type *str, streamsize count);
basic_istream& getline(char_type *str, streamsize count, char_type delim);

The first argument is a pointer to char_type. You on the other hand are passing a pointer to a 2D array of integer.

You will need to read in  the integer values as strings ( eg "123") or at least a series of char and then convert from char string to integer.

 

by: vwpsPosted on 2009-04-18 at 20:23:18ID: 31571901

Thanks a lot!

 

by: ewest02Posted on 2009-04-18 at 20:25:55ID: 24177822

NOTE:  The variants of getline() and getdelim() as suggested by doraemon2555 are not C or C++ standard functions. These are GNU C extensions. Use them at your own risk...

  --Eric

 

by: supergokhanPosted on 2009-06-23 at 03:09:01ID: 24690432

You read it to 2d array. Then you need to use getline like this

int i=0;
while(!sampleGrid.eof())
        {
                getline(myArr[i], 20, '\t');
                i++;
 
        }

                                              
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