Array of a struct with strings

Question

I have defined a structure

struct subject
{
    char name[100];
    int year;
};

and since I need n of these and I have to use malloc I did the following in my main function:

int n, i;
scanf("%d", &n);
struct subject *ptr = malloc(n*sizeof(struct subject));

Unfortunately when I try to input something with this code:

for(i = 0; i < n; i++)
{
   gets((ptr + i)->name);
   scanf("%d", (ptr + i)->year);
}

It crashes after I type the first name. The task requires the use of malloc.

Here's the whole code (unfortunately it's in my native language so it's a little bit different)

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

#ifndef DEBUG
#define DEBUG(...)printf(_VA_ARGS_)
#endif

struct kolegij
{
    char naziv[100];
    int semestar;
};

int main(){
    int brPredmeta, i;

    scanf("%d", &brPredmeta);

    struct kolegij *ptr = malloc(brPredmeta*sizeof(struct kolegij));

    if(ptr == NULL)
    {
       printf("error\n");
       return 0;
    }

    for(i = 0; i < brPredmeta; i++)
    {
       //gets(ptr->naziv);
       gets((ptr + i)->naziv);
       scanf("%d", &(ptr + i)->semestar);
       getchar();
    }

    for(i = 0; i < brPredmeta; i++)
    {
       printf("%s\n", ptr[i].naziv);
       printf("%d\n", ptr[i].semestar);
    }

    return 0;
}

With regards to the duplicate issue. I believe this shouldn't be a duplicate since it's related to structs and pointers. I had issues with scanfs before and I haven't considered this as a solution so I think it shouldn't be flagged as a duplicate.

Your second scanf needs a pointer to the variable you read into. Add a &. — Thomas Padron-McCarthy, Apr 29 '15 at 19:31
I added a & to the scanf but now it stops taking input after the first name and year and it prints out the following RANDOMNUMBER Subject Name Subject Year — RidableCthulu, Apr 29 '15 at 19:34
The newline character from the ENTER key is in the input buffer. Simplest (but brittle) solution is to add a getchar(); after the scanf. — Thomas Padron-McCarthy, Apr 29 '15 at 19:35
@ammoQ I have an if which checks that and it didn't return anything. — RidableCthulu, Apr 29 '15 at 19:40
@ThomasPadron-McCarthy I tried getchar(); but it still doesn't work. It cuts the first letter of first name, I can input n-1 data and it still outputs a random number before everything. — RidableCthulu, Apr 29 '15 at 19:40
`gets()`? You should be using `fgets()` instead, which is safer. — Jamal, Apr 29 '15 at 19:41
@Jamal I tried with both functions, however in both cases it's the same. — RidableCthulu, Apr 29 '15 at 19:41
It was a general note, which is why I didn't post it as an answer. — Jamal, Apr 29 '15 at 19:43
You need to post a minimal, compilable program that still shows the problem. The code that prints your random number, etcetera, is missing, so we can only guess what's wrong. — Thomas Padron-McCarthy, Apr 29 '15 at 19:43
@RidableCthulu Since you are allocating with `malloc` anyway, it would be simpler to just allocate `name` as well. Declare it as `char *name;` and then to fill it. just use `fgets (buf, BUFSIZE, stdin);`, then `ptr[i] = strdup (buf);`. Just don't forget to free it later. — David C. Rankin, Apr 29 '15 at 19:52
You're missing a getchar(); after the first scanf too. The newline character from when you pressed the ENTER key after that number is left in the input buffer, and is read by gets as a (very short) line. — Thomas Padron-McCarthy, Apr 29 '15 at 19:52
@ThomasPadron-McCarthy Thank you so much. I knew it had to be something with input. Did I mention I hate buffers in C? It is definitely the source of most of my problems in this subject. I never had any problems like this with C++. Thanks again! — RidableCthulu, Apr 29 '15 at 19:54
possible duplicate of [C: Multiple scanf's, when I enter in a value for one scanf it skips the second scanf](http://stackoverflow.com/questions/9562218/c-multiple-scanfs-when-i-enter-in-a-value-for-one-scanf-it-skips-the-second-s) — Thomas Padron-McCarthy, Apr 29 '15 at 19:57
@RidableCthulu, the use of buffers, dynamic or static, and a full understanding of pointers is one of the greatest strengths of C. While it may take a little effort learn, it is well worth the time spent. You want to change your outlook from **I hate buffers in C**, to **I love buffers in C**. You won't believe what a whole new world of programming will open up `:p` — David C. Rankin, Apr 29 '15 at 20:20

user2700896 · Answer 1 · 2015-04-29T19:43:32.353

-6

Malloc returns a void pointer type. In order to use it as a pointer to your structure you have to cast it first. Try changing the line with malloc into:

int n, i;
scanf("%d", &n);
struct subject *ptr = (struct subject*) malloc(n*sizeof(struct subject));

You also have to change your input into:

for(i = 0; i < n; i++)
{
   gets((ptr + i)->name);
   scanf("%d", &((ptr + i)->year));
}

edited Apr 29 '15 at 19:43

answered Apr 29 '15 at 19:35

user2700896

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1

This is double-wrong. First, it is not the cause of the problem, and second, this: http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc – Thomas Padron-McCarthy Apr 29 '15 at 19:36

Array of a struct with strings

1 Answers1