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Read text files with different column lengths

Jan 14, 2009 at 2:03am
fab10ab (2)
Hello, how do I get Visual C++.NET to read a text file for which the columns have different lengths? I have a text file like so:


40 50 51
12 48 7
10 13
18
155

I want C++ to read in three vectors from this text file, of size 3, 5, and 2, respectively. Are there column "pointers" that can be used for this?
The numbers are nicely aligned, exactly as they appear, and I can use space, tabs, or other delimiters. This is because I am exporting the numbers from Excel to a text file for reading into C++, so I can modify their format. Some numbers will have 2 digits, others 3 or 4. Finally, I would like to do this without switching the columns around in the text file.

Thanks!
Last edited on Jan 14, 2009 at 2:31am
Jan 14, 2009 at 2:14am
seymore15074 (449)
Tell us more about the data file. Is it constant or can you change its format? Are those spaces or tabs? Are the numbers all 2 digits? Are the numbers all aligned nicely like the example?
Jan 14, 2009 at 12:05pm
Faldrax (324)
It look as as though you have a specific format to the data - I am assuming you will be producing a lot of these small files over time and just need to process them in a particular way, so do not need a genric way of reading the text file per se.

To read the textfile you use the StreamReader class, and the ReadLine() method - this will read the data one line at a time into a String.
You can then use the String methods IndexOf() (to find the next delimimter), Substring (to get specific parts of the string) and Trim() to remove excess whitespace.
To Convert the string to an Int you can use the Parse() method of the Int32 Class (once you have a string that only contains the number).


Jan 14, 2009 at 6:44pm
chris (82)
A quick thing I did, took your test data & put it in a file called test.txt, this could give a basic outline to your program, uses this function http://www.cplusplus.com/reference/clibrary/cstdio/fscanf.html for easy reading of numbers from a file.
Hope this helps:
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#include<stdio.h>
int main()
{
FILE* file=fopen("test.txt","rb");
int n[3];
fscanf(file,"%d%d%d",&n[0],&n[1],&n[2]);
printf("n[0] = %d\nn[1] = %d\nn[2] = %d\n",n[0],n[1],n[2]);
getchar();
return 0;
}
Edit & run on cpp.sh
Jan 28, 2009 at 9:51pm
fab10ab (2)
Thanks Chris, but it seems the code is printing the first line only. This is the output I get:

n[0] = 40
n[1] = 50
n[2] = 51

I want to create and store three separate vectors, of lengths 3, 5, and 2 respectively. Any ideas?

Thanks everyone.
Jan 28, 2009 at 11:17pm
Duthomhas (13173)
As this is C++ question the answer should use C++.

You haven't answered seymore15074's questions, which are vital to answering your question.

If the file is simply aligned within a specific number of spaces per column, then you can use the std::string::substr() function to split out the columns.

If the columns are separated by, say, a single tab, then you can use the getline() function to read each column:
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#include <fstream>
#include <iostream>
#include <string>
using namespace std;

...

// read the three columns
string columnstrings[ 3 ];
for (int i = 0; i < 3; i++)
  getline( thefile, columnstrings[ i ], '\t' );

...


Once you have separated out a string containing a number, use a stringstream to extract the number:
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#include <string>
#include <stringstream>
using namespace std;

...

string numberstring = "   97";
int number;

// convert the number string to an actual number
// (invalid numbers --> zero)
if (!(istringstream( numberstring ) >> number)) number = 0;

...



If your file format is more sophisticated than fixed positions or a CSV, then you will need to ask your professor if you can simplify it.

Hope this helps.
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