Read space delimited file with variable number of columns in C - c

Question

So I have files formatted as follows:
2
4 8 4 10 6
9 6 74
The first line is actually the number of rows that the file will have after it. I want to read the files line by line (note there are different number of tokens in each line but all have the format: 1 token and then an unspecified number of pairs of tokens) and do two things for each line:
1) Know how many tokens are in this line.
2) Assign each token to a variable. Using structures similar to:
typedef struct {
unsigned start; //start node of a graph
unsigned end; // end node of a graph
double weight; //weight of the edge going from start to end
} edge ;
typedef struct {
unsigned id; // id of the node
unsigned ne; // number of edges adjacent to node
edge *edges; // array of edge to store adjacent edges of this node
} node;
Some code:
FILE *fin;
unsigned nn;
node *nodes;
fin = fopen ("input.txt", "r");
fscanf(fin,"%u\n", &nn);
nodes = malloc(nn*sizeof(node));
for(i=0; i < nn; i++) { //loop through all the rows
/*grab the row and split in parts, let's say they are part[0], part[1]... */
/*and there are N tokens in the row*/
nodes[i].id=part[0];
nodes[i].ne=(N-1)/2; //number of pairs excluding first element
nodes[i].edges=malloc( (N-1)/2)*sizeof(edge) );
for(j=0; j< (N-1)/2; j++){
nodes[i].edges[j].start=part[0];
nodes[i].edges[j].end=part[2*j+1];
nodes[i].edges[j].weight=part[2*j+2];
}
}
I need to figure out how to do the part comented inside the first for loop to get the number of tokens and each one of them as a simgle token to asign. Any ideas?
EDIT: to make things clear, each line will have first one integer, and then a variable number of pairs. I want to store data as follows:
if the file reads
2
4 8 4 10 6 //(2 pairs)
9 6 74 //(1 pair)
then
nn=2;
node[0].id=4;
node[0].ne=2; //(2 pairs)
node[0].(*edges) //should be a vector of dimension ne=2 containing elements of type edge
node[0].edges[0].start=4; //same as node[0].id
node[0].edges[0].end=8;
node[0].edges[0].weight=4;
node[0].edges[1].start=4; //same as node[0].id
node[0].edges[1].end=10;
node[0].edges[1].weight=6;
node[1].id=9;
node[1].ne=1; //(1 pair)
node[1].(*edges) //should be a vector of dimension ne=1 containing elements of type edge
node[1].edges[0].start=9; //same as node[1].id
node[1].edges[0].end=6;
node[1].edges[0].weight=74;

Answer 1

This code produces the results you described, It initializes your nested struct member edge, and uses strtok. With strtok(), I included the \n as part of the delimiter in addition to a space " \n" to prevent the newline from giving us trouble (see other comments on that below)
Note: you have to free memory where I have indicated, but before you do, preserve the intermediate results (in the structs) or it will be lost.
#include <ansi_c.h>
typedef struct {
unsigned start;
unsigned end;
double weight;
} edge ;
typedef struct {
unsigned id;
unsigned ne;
edge *edges;
} node;
int GetNumPairs(char *buf);
int main(void)
{
FILE *fp;
char *tok;
char lineBuf[260];
int i=0, j=0;
int nn; //number of nodes
char countPairsBuf[260];
fp = fopen("C:\\dev\\play\\numbers.txt", "r");
//get first line of file for nn:
fgets (lineBuf, sizeof(lineBuf), fp);
nn = atoi(lineBuf);
//create array of node with [nn] elements
node n[nn], *pN;
pN = &n[0];
//read rest of lines, (2 through end)
i = -1;
while(fgets (lineBuf, sizeof(lineBuf), fp))
{
i++;
//get number of items in a line
strcpy(countPairsBuf, lineBuf);
pN[i].ne = GetNumPairs(countPairsBuf); //number of edges (pairs)
if(pN[i].ne > 0)
{ //allocate *edges struct element
pN[i].edges = malloc((pN[i].ne)*sizeof(edge));
//get first item in new line as "line token" and "start"
tok = strtok(lineBuf, " \n");
while(tok)
{
pN[i].id = atoi(tok);
//now get rest of pairs
for(j=0;j<pN[i].ne;j++)
{
pN[i].edges[j].start = pN[i].id;
tok = strtok(NULL, " \n");
pN[i].edges[j].end = atoi(tok);
tok = strtok(NULL, " \n");
pN[i].edges[j].weight = atoi(tok);
}
tok = strtok(NULL, " \n"); //should be NULL if file formatted right
}
}
else //pN[i].ne = -1
{
//error, file line did not contain odd number of elements
}
}
//you have to free memory here
//but I will leave that to you
fclose(fp);
}
//GetNumPairs
int GetNumPairs(char *buf)
{
int len = strlen(buf);
int numWords=0, i, cnt=0;
for(i=0;i<len;i++)
{
if ( isalpha ( buf[i] ) ) cnt++;
else if ( ( ispunct ( buf[i] ) ) || ( isspace ( buf[i] ) ) )
{
numWords++;
cnt = 0;
}
}//if odd number of "words", return number of pairs, else error
return (((numWords-1)%2) == 0) ? ((numWords-1)/2) : (-1);
}