Question

How do I parse out the fields in a comma separated string into a integer array in C?

Input file date is like below-

6
1,2,77
1,5,32
1,3,54
2,4,12
4,5,52
4,3,56
6,2,8
6,5,30
3,6,44

I need those data will be stored in a array[u][v]. u = 1st column, v = 2nd column. and value of this array will be 3rd item of each row. Please help me out

Answer 1

Am I right that the first line gives the size of the array? I take this as an assumption.

The parsing of the string is done with scanf() in C and the stream extractor operator in C++. It requires a bit of care to handle the commas and newlines correctly.

The next problem I see is not directly related to the “parsing” problem, it is the handling of the integer array. Do you want that dynamic or static? (static means: the size of the array is known at compile time). If you want to have it dynamic you cannot use constructs like this: array[u][v] = value; in C. In C++ you can, but you need to declare the array correctly. Both of my solutions below use dynamic arrays.

C

This is a solution in pure C.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
  int size, u, v, value;
  FILE * pFile;
  int *array;

  pFile = fopen ("data.txt","r");

  fscanf (pFile, "%d", &size);   // reading the first line here

  array = malloc(size*size*sizeof(int)); // allocate the array based on size of first line
  memset(array,0,size*size*sizeof(int)); // set the array to zero

  while(!feof(pFile))       // read until the end...
  {
    fscanf(pFile, "%d,%d,%d\n", &u, &v, &value); // read 3 integer values
    array[(u-1)*size + v] = value;  // we have to calculate the index ourselves
  }
  fclose(pFile);    // we are done with reading

  // the follwing prints the contents of the array to visualize
  for(u = 1; u<=size; ++u)
  {
    for(v=1; v<=size; ++v)
      printf("%d, ", array[(u-1)*size+v]);
    printf("\n");
  }

  free(array);  //
  return 0;
}

C++

here the same thing in C++. However, it does not use STL containers for the dynamic array, which could be more “elegant”.

#include <fstream>
#include <iostream>
#include <cstring>

using namespace std;

int main()
{
  char c;
  int size, u,v,value;

  fstream file("data.txt");
  file >> size;

  int array[size+1][size+1] ;
  memset(array,0,sizeof(array));

  while(file.good())
  {
    file >> skipws >> u >> c >> v >> c >> value;
    array[u][v] = value;
  }

  for(u = 1; u<=size; ++u)
  {
    for(v=1; v<=size; ++v)
      cout <<  array[u][v] << ", ";
    cout << "\n";
  }
  file.close();
}