C: Newbie attemping file reading and struct allocation using malloc - c

Question

I am trying to store the values stored in a details.txt file into their appropriate place in a dynamically allocated struct. Am I doing something (that should be simple) incorrectly for this not to work? Is it necessary for me to use strtok and split by ','?
My details.txt reads:
mitch,8,1.78,burgers
murray,42,6.5,lasagna
travis,64,1.85,sushi
sam,12,1.94,bacon
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define BUFFERSIZE 256
typedef struct
{
char name[BUFFERSIZE];
int favnumber;
float height;
char favfood[BUFFERSIZE];
} Person;
void print_person(Person *p)
{
printf("name: %s\n", p->name);
printf("num: %d\nheight: %.2f\nfav. food: %s\n\n",
p->favnumber, p->height, p->favfood);
}
int count_lines(FILE *fp)
{
int nlines = 0;
char c;
for (c = fgetc(fp); c != EOF; c = fgetc(fp))
{
if (c == '\n')
{
nlines++;
}
}
rewind(fp);
return nlines;
}
int main(void)
{
FILE *fp = fopen("details.txt", "r");
// count lines
int nlines = count_lines(fp);
printf("found %d lines\n\n",nlines);
Person *people = (Person*)malloc(nlines*sizeof(Person));
char buffer[BUFFERSIZE];
int i = 0;
while (fgets(buffer,BUFFERSIZE,fp) != NULL)
{
sscanf(buffer,"%s%d%f%s",people[i].name,
&(people[i].favnumber),
&(people[i].height),people[i].favfood);
print_person(&(people[i]));
i++;
}
printf("found %d people\n",i);
free(people);
fclose(fp);
}
Unfortunately, the current output of my program is:
found 4 lines
name: mitch,8,1.78,burgers
num: 0
height: 0.00
fav. food:
...
found 4 people

Answer 1

The problem is that the first %s parse the the whole line, and you need , in the format string to separate the fields. Not an issue here yet but I also used %[^,] for the last format string so it will not stop at the first space. Also added precision on the strings to avoid buffer overflows:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define BUFFERSIZE 255
#define str(s) str2(s)
#define str2(s) #s
typedef struct
{
char name[BUFFERSIZE+1];
int favnumber;
float height;
char favfood[BUFFERSIZE+1];
} Person;
void print_person(Person *p)
{
printf("name: %s\n", p->name);
printf("num: %d\nheight: %.2f\nfav. food: %s\n\n",
p->favnumber, p->height, p->favfood);
}
int count_lines(FILE *fp)
{
int nlines = 0;
char c;
for (c = fgetc(fp); c != EOF; c = fgetc(fp))
{
if (c == '\n') {
nlines++;
}
}
rewind(fp);
return nlines;
}
int main(void)
{
FILE *fp = fopen("details.txt", "r");
// count lines
int nlines = count_lines(fp);
printf("found %d lines\n\n",nlines);
Person *people = (Person*)malloc(nlines*sizeof(Person));
char buffer[BUFFERSIZE+1];
int i = 0;
while (fgets(buffer,BUFFERSIZE+1,fp) != NULL)
{
// Changed line, see formatting of %s
sscanf(buffer,
"%" str(BUFFERSIZE) "[^,],%d,%f,%" str(BUFFERSSIZE) "[^,]",
people[i].name,
&(people[i].favnumber),
&(people[i].height),people[i].favfood);
print_person(&(people[i]));
i++;
}
printf("found %d people\n",i);
free(people);
fclose(fp);
}