Saving a string from a text file to a struct using fscanf (C)

Question

Sample Text file:

234765 PETER 
867574 SMITH 

---

I'm trying to take the id and string from the text file and save it into a struct. The id is saving fine but the string isn't.

typedef struct student 
{
    int id[DATA_SIZE];
    char *student[DATA_SIZE];
}studentinfo;
studentinfo list;

struct student *create_space(int size)
{
    struct student *tmp = (struct student*)malloc(size*sizeof(struct student));
    return(tmp);
}
struct student * readData(struct student*pointer,studentinfo v)
{
    int count =0;
    int tmpid;
    char str[256];
    FILE* in_file; 
    in_file = fopen("studentlist.txt","r");
    while(fscanf(in_file,"%d",&tmpid)!= EOF && count<DATA_SIZE)
    {
        fscanf(in_file,"%s",v.student[count]);
        //printf("%s\n",str );
        v.id[count]=tmpid;
        count++;
    }
    pointer =&v;
    return pointer;

}
int main()
{
    struct student *data;
    struct student *sdata;
    data = create_space(1);
    sdata = readData(data,list);
    //printf("%s\n",sdata->student[2] );

}

Answer 1

Their are a couple of issues:

• fscanf() reads formatted input, and returns the number of items read.

  This line:

   while(fscanf(in_file,"%d",&tmpid)!= EOF && count<DATA_SIZE)

  Could be this:

   while (count < DATA_SIZE && fscanf(in_file, "%d %255s", &list.id[count], str) == 2) {

  Which verifies that 2 values are being read on each line successfully.

• You are not checking if in_file returns NULL . It's safe to do this. This goes the same for malloc() .

• You need to correctly create space for char *students[DATA_SIZE] , as this is an array of char * pointers. Once you allocate space for this via malloc() or strdup() , then you can copy the contents into students .

  Here is an example of doing such a thing:

   while (count < DATA_SIZE && fscanf(in_file, "%d %255s", &list.id[count], str) == 2) { /* allocate space for one student */ list.student[count] = malloc(strlen(str)+1); if (!list.student[count]) { printf("Cannot allocate string\\n"); exit(EXIT_FAILURE); } /* copy it into array */ strcpy(list.student[count], str); count++; }

Here is an example that you can use to help achieve your desired result:

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

#define DATA_SIZE 256

typedef struct {
    int id[DATA_SIZE];
    char *student[DATA_SIZE];
} studentinfo_t;

int main(void) {
    FILE *in_file;
    studentinfo_t list;
    char str[DATA_SIZE];
    size_t count = 0;

    in_file = fopen("studentlist.txt", "r");
    if (!in_file) {
        fprintf(stderr, "%s\n", "Error reading file");
        exit(EXIT_FAILURE);
    }

    while (count < DATA_SIZE && fscanf(in_file, "%d %255s", &list.id[count], str) == 2) {
        list.student[count] = malloc(strlen(str)+1);
        if (!list.student[count]) {
            printf("Cannot allocate string\n");
            exit(EXIT_FAILURE);
        }
        strcpy(list.student[count], str);
        count++;
    }

    for (size_t i = 0; i < count; i++) {
        printf("%d %s\n", list.id[i], list.student[i]);
    }

    return 0;
}