Using fgets() and strtok() to read in a file line-by-line in C?

Question

I'm trying to use fgets and strtok() to read in a file line by line, and create a linked list of each different line of information.

Right now, I'm only just putting the information into an array, just to try to figure out how to read the information in correctly, but it's not working right.

In the while(fgets) portion, it seems to load everything into the array properly, and prints it out. However, after that loop has executed and I try to print out the whole array, I get really weird results.. which is mostly portions of the last line ONLY, and not complete words or anything for the most part.

For example, if I'm reading in:

Simpson, Homer, Male, 1976
Simpson, Marge, Female, 1978
Simpson, Bart, Male, 2002 
Simpson, Lisa, Female, 2004 
Simpson, Maggie, Female, 2011 

The printout I get at the end is something like:

le
Simpson
 Maggie


Simpson
 Maggie
e
ale
Simpson
 Maggie
e
e
Simpson
 Maggie
 Female
 2011

Please let me know where I'm going wrong, thanks!

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXSTRINGSIZE 10
#define LINESIZE 128

struct person{
    char firstName[MAXSTRINGSIZE];
    char lastName[MAXSTRINGSIZE];
    char gender[MAXSTRINGSIZE];
    int birthYear;
    struct person *next;
} *first, *current;


int main (void){
    static const char filename[] = "Assignment1file.txt";
    FILE *myfile = fopen ( "Assignment1file.txt", "r" );

    int i=0;
    int j=0;
    int k=0;
    int l=0;
    char *result[10][4];
    char line[LINESIZE];
    char *value;

    for(i=0; i<9; i++){
        for(j=0;j<4;j++){
            result[i][j] = NULL;
        }
    }
    i=0;

    // loop through each entry in Assignment1file
    while(fgets(line, sizeof(line), myfile)){

        //load last name
        value = strtok(line, ",");
        result[i][0] = value;
        printf("%i 0 %s", i, value);


        //load first time
        value = strtok(NULL, ",");
        result[i][1] = value;
        printf("%i 1 %s", i, value);

        // load gender
        value = strtok(NULL, ",");
        result[i][2] = value;
        printf("%i 2 %s", i, value);

        // load birth year
        value = strtok(NULL, "\n");
        result[i][3] = value;
        printf("%i 3 %s", i, value);
        printf("\n");

        for(j=0;j<4;j++){
            printf("%s\n", result[i][j]);
        }


        //go to next line
        i++;
    }   

    // read out the array
    for(k=0; k<5; k++){
        for(j=0;j<4;j++){
            printf("%s\n", result[k][j]);
        }
    }

    fclose(myfile);
    return 0;
}

Answer 1

strtok() returns pointers inside line[] so when you read the next line all the pointers you saved are now pointing to places where the last line of the file is stored.

You could allocate memory for each bit of string like so:

//load last name
value = strtok(line, ",");
result[i][0] = malloc(strlen(value) + 1);
strcpy(result[i][0], value);

As an aside, you don't need the loops at the start to set everything to NULL, you could do this instead:

char *result[10][4] = {0};