Reading from file into 2D char array

Question

What I'm trying to do is simple in concept, but I can't quite get it to work in practice.

I have a file that I'm trying to read from, there's 3 columns. The first and second are integer columns while the third contains a string.

I'm taking the contents of this file and writing them into a series of arrays. My problem lies in the character array, which is two dimensional.

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

#define NUMBER 128  //Maxmimum number of items/lines in file.
#define BUFFER 120  //Buffer length.
#define LENGTH 32   //Maximum length of lines in file.

//------------------------Global Variables. ---------------------------------------------
int iterations=0;   //Will count number of times the calculation function is called. 

int weight[NUMBER];     
int value[NUMBER];      
char object[NUMBER][LENGTH];        

//------------------------Main. ---------------------------------------------------------
int main(void)
{
    FILE *fp;   //File pointer.
    char buffer[120];   //Temporary storage
    int result;
    int i,j=0;

    int weight[NUMBER];     
    int value[NUMBER];      
    char object[NUMBER][LENGTH];    

    fp=fopen("knapsack.data","r");
    if(NULL==fp){
        printf("Error opening file. \n");
        exit(0);
    }

//Print the file.   
    printf("Weight \t Value \t Object \n");

    for(i=0;i<=NUMBER;i++){
        while(NULL != fgets(buffer, 120, fp)){
                result=sscanf(buffer, "%d %d %s", &weight[i], &value[i], object[i][0]);
                printf("%d \t %d \t %s \n", weight[i], value[i], object[i][0]);
        }
    }
    for(j=0;j<4;j++){
        printf(" String i equals %s \n", object[j]);
    }

    fclose(fp);
}

The problem I'm encountering is that upon printing, I find that the contents of the strings column is (null) like so:

Weight   Value   Object
1        10      (null)
2        25      (null)
5        40      (null)
7        100     (null)

Should I be trying to parse the file in another way, or is it just something small I'm missing? Thanks in advance.

Answer 1

You need an ampersand &object[i][0] in both sscanf and printf. Also, the compiler might complain about type error, in which case you will also need to cast: (char *)&object[i][0]

Answer 2

Either use &object[i][0] or object[i] (they can both be used interchangeably, they mean the same thing with c strings)

As far as your output and why it's not printing successfully, it has to do with the way you are reading in the data from the file. You are using a while loop when you should be using an if statement inside the while loop to check for the iterations reaching NUMBER of times run. Something like this should work:

i = 0;
while(NULL != fgets(buffer, 120, fp))
{
    if(i < NUMBER)
    {
        result = sscanf(buffer, "%d %d %s", &weight[i], &value[i], object[i]);
        printf("%d \t %d \t %s \n", weight[i], value[i], object[i]);
        i++;
    }
}

I tested this out with your code and a sample knapsack.data file that I created and it works just fine on both parts, without the & by the way :)