CODEWITHSUNDEEP
carraysstruct
hii
hii

Reputation: 100

How to read pointer values into an array of structs

I have following struct

typedef struct
{
    char* city;
    int temp;
} Place;`

I am attempting to read in two values from a line into an array of structs.

The lines look like:

Los Angeles; 88

I am attempting to read data into the array. Assuming my memory allocation is correct what is the correct way to read in these values.

my code

    void readData(FILE** fpData, FILE** fpOutput)
{
    char s[100];
    int index = 0;

    Place *values;
    values=malloc(size * sizeof(Place));
    if (values == NULL)
    {
        MEM_ERROR;
        exit(1);
    }


    for (int a = 0; a < size; a++)
    {
        (values[a]).city = (char *) malloc(100 * sizeof(char));
        if(values[a].city == NULL)
        {
            MEM_ERROR;
            exit(100);
        }
    }

    while(fgets(s, sizeof(s), *fpData)!=NULL)
    {
        sscanf(s, "%[^:]%*c%d\n", values[index].city, &values[index].temp);
        index++;
    }

    sortInsertion(values, size, fpOutput);

    free(values);
    return;
}

The city is not going into the array so I am assuming the part where it says values[index].city is incorrect.

How can I fix this ?

Upvotes: 0

Views: 114

Answers (2)

tivn
tivn

Reputation: 1923

Your data using semicolon ; while your sscanf format using colon :, make sure this is same character. If your data really use semicolon, change %[^:] part in the sscanf format to %[^;]

Here my code and how I run it to show you that it works:

#include <stdio.h>

struct Place {
    char city[100];
    int  temp;
} values[30];

int main() {
    char s[100];
    int i=0, n=0;
    while ( fgets(s, sizeof(s), stdin) != NULL ) {
        sscanf(s, "%[^;]%*c%d\n", values[n].city, &values[n].temp);
        n++;
    }
    printf("n=%d\n", n);

    for ( i=0; i<n; i++ ) {
        printf("values[%d] = (%s, %d)\n", i, values[i].city, values[i].temp);
    }
}

This is how I run it on Linux:

% for a in `seq 1 3`; do echo "City-$a; $a$a"; done | ./a.out 
n=3
values[0] = (City-1, 11)
values[1] = (City-2, 22)
values[2] = (City-3, 33)

Upvotes: 4

Chris Dodd
Chris Dodd

Reputation: 126223

sscanf(s, "%[^:]%*c%d\n", values[index].city, &values[index].temp);

This will copy everything from the start of the line read up to the first colon (:) into the city array you allocated. Your example input would seem to have a semi-colon (;), so you'll get the entire line in the city array and nothing in the temp field.

You don't do any input checking, so any too-long input line will get split into multiple (probably corrupted) cities. You'll also have problems if there are not exactly size lines in the file, as you don't check to make sure index doesn't go past size while reading, and you assume you have size entries at the end without checking.

Upvotes: 2

Related Questions