array of structs in c-user input - c

Question

I am new to programming in general and to C in particular.
I am trying to write a program that uses an array of structs, but I am experiencing problems if that struct contains strings.
Somehow the compiler crashes after the user has given the last input.
The struct below is just a simplified version containing only one item, because the problem seems to be reading strings into the array.
Any help is much appreciated, thanks in advance.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct
{
char* name;
}student;
int main()
{
int size;
printf("enter number of entries\n");
scanf("%d" , &size);
student* all=malloc(size*sizeof(student));
int i;
for(i=0;i<size;i++)
{
printf("enter name\n");
scanf("%s" , all[i].name);
}
return 0;
}

Answer 1

Before taking input scanf("%s" , all[i].name); , you need to allocate memory to all[i].name .
An example-
for(i=0;i<size;i++)
{
all[i].name=malloc(20*sizeof(*(all[i].name)));
if(all[i].name!=NULL){
printf("enter name\n");
scanf("%19s" , all[i].name);
}
}
//use these strings
for(i=0;i<size;i++){
free(all[i].name); //free the allocated memory
}
free(all);
Or in your structure instead of char * ,declare name as a char array (if you don't want to use dynamic allocation)-
typedef struct{
char name[20]; //give any desired size
}student;
/* no need to free in this case */

Answer 2

No memory is allocated for the students names (char* name), so when trying to scanf to that pointer, invalid memory is accessed and the program crashes.
The easiest way is to declare name as an array: char name[28];
The return value of malloc() needs to be checked too, in case there was problem allocating the memory for the students, which would return a NULL pointer. At the end, the allocated memory needs to be freed with free().
For example:
#include <stdio.h>
#include <stdlib.h>
typedef struct {
char name[28];
unsigned int age;
} student;
int main()
{
size_t size = 0;
printf("\nEnter number of entries: ");
scanf("%zu", &size);
// add some check for size
student* students = (student*)malloc(size * sizeof(student));
if (students == NULL) {
printf("\nProblem with allocating memory:\n"
" - size: %zu\n"
" - total size needed: %zu\n",
size, size * sizeof(student));
return 0;
}
for (size_t i = 0; i < size; ++i) {
printf("Enter name: ");
scanf("%27s", students[i].name);
printf(" Enter age: ");
scanf("%u", &students[i].age);
}
printf("\nList of students:\n");
for (size_t i = 0; i < size; ++i) {
printf("%s (%u)\n", students[i].name, students[i].age);
}
free(students); // free the allocated memory
return 0;
}