loading values of a text file into an array - c++

Question

The text file I generate from an graph generator is similar to:
:0 0|- 1|82 2|72
:1 0|87 1|- 2|74
:2 0|86 1|53 2|-
These are supposed to represent node and the distance to them.
line 1 is :1 1|- 2|82 3|72
it is saying the distance from node 0 to node 0 (0|-) is - (infinity)
and from node 0 to node 1 (1|82) is 82
and from node 0 to node 2 (2|72) is 72
But I want to load the values into a 2d array.
the array above should be
Graph[0][0] = -
Graph[0][1] = 82
Graph[0][2] = 72
etc...
I'm just not sure how when I read in the txt file to catch the :0 & :1 & :2 then separate 1|5.
any help would be great!
Thanks!

Answer 1

One problem is those - characters. If you replace them with 0, then you can use something like the following code:
// Open the file like this:
// std::ifstream fin ("whatever.txt");
char dummy;
for (int i = 0; i < n; ++i)
{
int x, d;
fin >> dummy >> x; // read ":1", etc.
assert (dummy == '=');
assert (x == i + 1);
for (int j = 0; j < n; ++j)
{
fin >> x >> dummy >> d; // read "2|42", etc.
assert (dummy == '|');
assert (x == j + 1);
Graph[i][j] = d;
}
}
All those asserts are there to make sure the redundant data in the file are as they are supposed to be. And don't forget to replace all '-'s with '0's.
You can see what I'm doing there. I'm reading the integers normally, and reading a character when the ':' and '|' symbols are.

Answer 2

A plain C approach which you may re-write as C++ or just use as-is. After all, this doesn't look like C++ critical code.
Note the use of a maximum length for fgets (granted, a C++ string could work better here) and a #define for "infinity", since you cannot store this value in a sensible way. It assumes all of your distances are positive, and that your data is as you have shown (i.e., no surprises such as huge numbers > MAX_INT, or inconsistent spacing).
The usual C++ approach of cin does not work well here, and neither does fscanf, since in both cases you need to read one character, determine if it is an - and if it is not re-read itself and any digits following it.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_DATA_LENGTH 120
#define DIST_INFINITY 0xFFFFFFFF
unsigned int Graph[10][3];
int main (void)
{
FILE *fp;
char input_string[MAX_DATA_LENGTH], *token_ptr;
int graph_counter = 0, i;
fp = fopen ("graph.txt", "rt");
if (!fp)
{
printf ("data not found\n");
return -1;
}
do
{
if (fgets (input_string, MAX_DATA_LENGTH, fp) == NULL)
break;
token_ptr = input_string;
for (i=0; i<3; i++)
{
token_ptr = strchr (token_ptr, '|');
if (!token_ptr || !token_ptr[1])
break;
token_ptr++;
if (*token_ptr == '-')
Graph[graph_counter][i] = DIST_INFINITY;
else
Graph[graph_counter][i] = strtoul (token_ptr, NULL, 10);
token_ptr++;
}
if (i < 3)
break;
graph_counter++;
} while (1);
for (i=0; i<graph_counter; i++)
printf ("Graph[%d] = %u %u %u\n", i, Graph[i][0], Graph[i][1], Graph[i][2]);
return 0;
}