How to read a txt file into a 2d array - c++

Question

Hey guys I am new to reading txt files to arrays, so I need to read this txt file temperature.txt to a two dimensional array. Here is the file I need to read, and the code I tried writing up it complies but Im not sure if it is reading it correctly
T(F) R1 R2 R3 R4
95.0 95.20 66.10 43.10 29.00
96.0 96.10 67.60 43.50 31.20
97.0 97.40 67.00 43.70 30.50
98.0 97.20 69.10 44.10 30.70
99.0 98.90 68.00 44.70 32.80
100.0 99.50 71.10 45.10 31.50
101.0 101.00 71.20 45.30 31.60
102.0 101.60 71.00 45.70 30.50
103.0 101.80 73.10 46.30 32.50
104.0 103.70 73.50 46.60 32.70
105.0 105.60 72.80 47.10 33.60
UPDATE I re did this again without looking at your answers but will this work ?
using namespace std;
#include<fstream>
#include<iostream>
#include<cmath>
#include<iomanip>
#include<stdlib.h>
int main ()
{
char temp[11] [5];
ifstream tempin ("c:\\mydoc2\\temperaturedata.txt");
tempin>>temp[0]>>temp[1]>>temp[2]>>temp[3]>>temp[4]>>temp[5]>>temp[6]>>temp[7]>>temp[8]
>>temp[9]>>temp[10];
while(!tempin.fail())
{
cout<< temp[0] << " " << temp[1] << " " << temp[2] << " " << temp[3]<< " " << temp[4]<< " " << temp[5] << " " << temp [6] <<
" " << temp [7] << " " << temp[8] << " " << temp[9] << " " << temp[10];
tempin>>temp[0]>>temp[1]>>temp[2]>>temp[3]>>temp[4]>>temp[5]>>temp[6]>>temp[7]
>>temp[8]>>temp[9]>>temp[10];
}
cout << endl << endl;
system("pause");
return 0;
}

Answer 1

You have a string myArray[5]; but you're reading 55 elements - that should not work!

Answer 2

There are lots of errors in your code.
1) You have written a read function but you never call it, so it never executes.
2) There is no 2D array in your code. 2D arrays look like this double myArray[10][10];. (that's a 10 by 10 2D array of doubles).
3) You're trying to read floating point numbers, but your array is an array of strings.
4) Your array is size 5 but you try and read 55 items into it.
5) After you open the file you have an infinite loop which just prints out "No file\n". Not sure why you want to print out error messages in a loop. Normally you just print an error message once.
I could go on, but I think the main point is that you're a beginner, and you currently aren't able to write three lines of code without introducing an error (sorry to be harsh but based on the above that is true). So the important lesson is that you should not try to write more than three lines of code at once.
Try something like this
a) Write some code which opens a file, test it and check that it does open the file
b) Add some code to a) to read one number, test it and check that it does read one number.
c) Replace the read one number code with code that reads a 1D array of numbers. Test it and check that it works.
etc. etc.
The point is to build up gradually to the program you want, and test each stage as you go. I can't emphasise how important that is. Every professional programmer works like this, but because you're a beginner the steps you have to take are much smaller than an experienced programmer.

Answer 3

Try something like this:
#include <stdlib.h>
#include <fstream>
#include <sstream>
#include <string>
#include <iostream>
using namespace std;
int main() {
string line;
ifstream myfile ("C:/temps.txt");
int dim_x = 12;
int dim_y = 5;
double temps[dim_x][dim_y] ;
//init the array if neccesary
for(int x = 0;x<dim_x;x++)
for(int y = 0; y<dim_y;y++)
temps[x][y]=0;
if (myfile.is_open()){
for ( int x=0; getline (myfile,line); x++ ){
int y=0;
istringstream iss(line);
while(iss){
string sub;
iss >> sub;
temps[x][y] = ::atof(sub.c_str());
y++;
}
}
myfile.close();
}
cout << "TEMPS:" << endl;
for(int x = 0;x<dim_x;x++){
for(int y = 0; y<dim_y;y++)
cout<<temps[x][y]<<" ";
cout<<endl;
}
return 0;
}

Answer 4

I made some improvements
#include <fstream>
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
void read ();
int main ()
{
read();
return 0;
}
void read()
{
ifstream indata(".\\temperaturedata.txt");
if(indata == NULL)
{
cout<< "Opening file failed."<< endl;
return;
}
const int columns = 5;
const int rows = 11;
double myArray[rows][columns];
string tmp;
getline(indata, tmp);
for(int i = 0; i < rows; ++i)
{
for (int j = 0; j < columns; ++j)
{
cout << "\t" << flush;
indata >> myArray[i][j];
cout.setf(ios::fixed);
cout << setprecision(2) << myArray[i][j] <<flush;
}
cout << endl;
}
indata.close();
}

Answer 5

If the content of your file is like this:
95.0 95.20 66.10 43.10 29.00
96.0 96.10 67.60 43.50 31.20
97.0 97.40 67.00 43.70 30.50
98.0 97.20 69.10 44.10 30.70
99.0 98.90 68.00 44.70 32.80
100.0 99.50 71.10 45.10 31.50
101.0 101.00 71.20 45.30 31.60
102.0 101.60 71.00 45.70 30.50
103.0 101.80 73.10 46.30 32.50
104.0 103.70 73.50 46.60 32.70
105.0 105.60 72.80 47.10 33.60
then, it's quite easy for you to get these values. But there are some errors in your code:
while(!indata.fail()) : This line will cause a dead loop. Use if(!indata) instead.
You will need a 2-dimension array of type double instead of string
Here is what could work:
#include<fstream>
#include<iostream>
#include<cmath>
#include<iomanip>
#include<stdlib.h>
using namespace std;
void read ();
int main ()
{
read();
system("PAUSE");
return 0;
}
void read()
{
ifstream indata("E:\\temperature.txt"); //that's my path,you should use yours.
if(!indata)
{
cout<<"No file."<< endl;
}
if(indata.is_open())
{
double myArray[11][5];
for(int i = 0; i < 11; ++i)
{
for(int j = 0; j < 5; ++j)
{
indata >> myArray[i][j];
//cout<<myArray[i][j]<<"\t";
}
//cout<<endl;
}
}
}
This could work when your txt file doesn't include the first line:T(F) R1 R2 R3 R4, if this line did exit,you should use getline() to move your file pointer to the second line, where you could read the data.