Creating a graph from a txt file in C - c

Question

I have a txt file, which contains groups of 3 elements in each line (2 strings for vertices and 1 integer for edge), which i want to use as input to create an adjacency list for a graph.
The txt file is as so: "string1 string2 34" and the elements are separated by tabs.
I've tried for starters trying to read from the file, using fgets , and managed to print the elements, but i'm stuck as to how i can parse them and store them. Any ideas?

Answer 1

A complete solution can be found at https://www.thecrazyprogrammer.com/2017/06/bellman-ford-algorithm-in-c-and-c.html
The Bellman-Ford algorithm in C is also discussed in https://stackoverflow.com/a/36831569/18980756.
Nevertheless, some code based on your input to put the elements into a dynamically allocated linked list:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct FORM {
char *vertice_one;
char *vertice_two;
int weight;
struct FORM *next;
} FORM;
int main() {
int err = 0; // error indicator
// helper to store temporarily store read values
char s1[256], s2[256];
int w;
FORM *firstEntry = NULL; // root element for the list
FILE *file = fopen("forms.txt", "r");
if (file == NULL) goto cleanup;
// read three line elements into variables
while (fscanf(file, "%s%s%d\n", &s1[0], &s2[0], &w) == 3) {
// print read elements for debugging purposes
printf("read: %s-%s-%d\n", s1, s2, w);
// dynamically allocate memory to store the read values
FORM *newEntry = malloc(sizeof *newEntry);
if (newEntry == NULL) {
fprintf(stderr, "Error - Not enough memory!");
err = 1;
goto cleanup;
}
char *vert1 = malloc(strlen(&s1[0]) + 1);
char *vert2 = malloc(strlen(&s2[0]) + 1);
if (vert1 == NULL || vert2 == NULL) {
fprintf(stderr, "Error - Not enough memory!");
err = 1;
goto cleanup;
}
memcpy(vert1, &s1[0], strlen(&s1[0]) + 1);
memcpy(vert2, &s2[0], strlen(&s2[0]) + 1);
newEntry->vertice_one = vert1;
newEntry->vertice_two = vert2;
newEntry->weight = w;
// put new entry to front a linked list
newEntry->next = firstEntry;
firstEntry = newEntry;
}
FORM *p = firstEntry;
while(p != NULL) {
printf("%s\t%s\t%d\n", p->vertice_one, p->vertice_two, p->weight);
p = p->next;
}
FORM *q;
cleanup:
q = firstEntry;
while(q != NULL) {
FORM *entry = q;
q = q->next;
if (entry->vertice_one != NULL) free(entry->vertice_one);
if (entry->vertice_two != NULL) free(entry->vertice_two);
free(entry);
}
if (file != NULL) {
fclose(file);
}
return err;
}
$ gcc -Wall -Wextra graph.c
$ ./a.out
read: vert1-vert2-1
read: vert3-vert4-2
vert3 vert4 2
vert1 vert2 1
$
Now you are in C land and can start thinking about how you want to work with the data read.
I guess
FORM should be named EDGE
vertex_one should be named source
vertex_two should be named destination
weight remains weight
You could avoid the dynamic allocation if you define arrays which are large enough to hold the data from the file.