scanf does not work - c

Question

im implementing a program that reads student id and names from stdin or file, and make them ordered by name and ordered by number. The funny thing is i cant understand why but scanf doesnt work. Here is my code while using scanf:
int n=0;
while(n<SIZE){
scanf("%d %s\n",&std_array[n].id, std_array[n].name);
n++;
}
for(int i=0; i<SIZE; i++)
printf("%d %s\n",std_array[i].id,std_array[i].name);
and here is my struct:
struct Student {
char *name;
int id;};
when i read from file and print them the out put is:
> 12586546 (null) 0 (null) 0 (null) 0 (null) 0 (null) 0 (null) 0 (null)
> 0 (null) 0 (null) 0 (null)
although file have some numbers and names like 21456764 john 45797654 fred etc. , its doesn't read successfully.
NOTE: i know the way we fix struct like you guys suggested but i must learn the way to do this with char pointer...

Answer 1

When doing this:
struct Student {
char *name; // This does not allocate memory
int id;};
Here, name is a pointer, with no allocated memory, behaving like an uninitialized literal string.
Trying to modify it creates undefined behaviour.
Replace with:
struct Student {
char name[50];
int id;};
or
struct Student {
char name[] = "Initial value gives maximum length. Do not write more!";
int id;};

Answer 2

This allocates memory to the pointer as needed. An intermediate variable is used to hold the string then only enough memory plus 1 for the terminating '\0' is allocated in the struct.
int n=0;
char name[100];//longest possible name
while(n<SIZE && ( scanf("%d%99s",&std_array[n].id, name) == 2)) {// successfully scanned two items
std_array[n].name = malloc ( strlen ( name) + 1));
if ( std_array[n].name == NULL) {
printf ( "malloc failed\n");
// break or return or exit(1) as appropriate
}
strcpy ( std_array[n].name, name);
n++;
}
for(int i = 0; i < n; i++)
printf("%d %s\n",std_array[i].id,std_array[i].name);
Eventually you will want to free the memory
for ( i = 0; i < n; i++) {
free ( std_array[i].name);
}

Answer 3

Point 1
Allocate memory to name before using it. Otherwise, if used uninitialized, it does not point to any valid memory to read from or write into. You can use malloc() to allocate memory. Also, once done, don't forget to free() it once you're done using the memory.
Point 2
Remove the \n from scanf().

Answer 4

This is the corrected code
struct Student
{
char name[20];
int id;
};
struct Student std_array[SIZE];
int n=0;
while(n<SIZE)
{
scanf("%d %s", &std_array[n].id, std_array[n].name);
n++;
}
n=0;
while(n<SIZE)
{
printf("%d %s\n", std_array[n].id, std_array[n].name);
n++;
}
Hope this helps...,

Answer 5

as user3121023 told to me, it worked. fixed code is following:
struct Student {
char *name;
int id;
};
struct Student std_array[SIZE];
int cmpfunc (const void * a, const void * b);
struct Student *order_by_number(struct Student *array);
int main(int argc, char **argv){
int n=0;
char name[100];
while(n<SIZE){
scanf("%d %s\n",&std_array[n].id, name);
std_array[n].name = malloc(strlen(name)+1);
strcpy(std_array[n].name ,name);
n++;
}
for(int i=0; i<SIZE; i++)
printf("%d %s\n",std_array[i].id,std_array[i].name);
order_by_number(std_array);
for(int i=0; i<SIZE; i++)
printf("%d %s\n",std_array[i].id,std_array[i].name);
}
im done, ty guys for helping me. CASE CLOSED :)