Using struct and point to input and output info - c++

Question

I have a problem with inputting a string pointer in struct. This is my code:
typedef struct{
char *name;
int age;
}stu;
void allocate(stu* &s, int n){
s = (stu*) malloc(n * sizeof(stu));
if(s == NULL){
printf("\nNot enought memory!");
exit(1);
}
}
// Input info
void input_info(stu* &s, int n){
void input(stu &s); //prototype
for(int i = 0; i < n; i++){
printf("\n-- Student #%d:", i+1);
input(*(s+i));
}
}
void input(stu &s){
fflush(stdin);
printf("\nEnter student's name: ");
gets(s.name);
printf("\nEnter student's age: ");
scanf("%d", &s.age);
}
// End input
//Output info
void output_info(stu* s, int n){
void output(stu s); //prototype
for(int i = 0; i < n; i++){
printf("\n-- Student #%d:", i+1);
output(*(s+i));
}
}
void output(stu s){
printf("\nName: %s", s.name);
printf("\nAge: %d", s.age);
}
//End output
int main(){
stu* s;
int n;
printf("How many students you want to input?: ");
scanf("%d", &n);
allocate(s, n);
input_info(s, n);
output_info(s, n);
getch();
}
When I input second student's name, it's breaked? I allocated memory. And I want to ask how to deallocate memory for stu pointer? Thanks for reading

Answer 1

There are many things that can and should be improved in your program. Some suggestions:
Remove the char * member replace it with std::string. You don't want to do manual memory management for anything unless you really want to.
Drop the silly scanf and printf, they are not type safe. Since you are using C++ use std::cin and std::cout and you are much safer than usage with later.
Drop the fflush(stdin), Calling fflush on anything other than stdout gives you undefined behavior.
In C++, You would usually want to use new and not malloc. Avoid using dynamic memory allocation at all, if you can. Prefer to use a std::vector instead.
Online Sample:
Following the above suggestions your example can be written as:
#include<string>
#include<vector>
#include<iostream>
typedef struct
{
std::string name;
int age;
}student;
// Input info
void input_info(std::vector<student> &s)
{
student obj;
std::cout<<"\nEnter Students name";
std::cin>>obj.name;
std::cout<<"\nEnter Students age";
std::cin>>obj.age;
s.push_back(obj);
}
// Output info
void output_info(const std::vector<student> &s)
{
for (auto itr = s.cbegin(); itr != s.cend(); ++itr)
{
std::cout<<"\nName:"<< itr->name;
std::cout<<"\nAge:"<< itr->age;
}
}
int main()
{
int n;
std::cout<<"How many students you want to input?\n";
std::cin>>n;
std::vector<student>s;
for(int i = 0; i<n; i++)
{
input_info(s);
}
output_info(s);
return 0;
}

Answer 2

As some of the previous poster have mentioned, the code is not "pure" c++, as it mixes a lot of C and C++ features. Personally I think it is a less problematic when dealing with POD structs, like yours.
The crash is likely caused by gets(). It assumes that the char pointer is already allocated with a suitable capacity. It has undefined behavior when the inputs strings is longer than the capacity. Your capacity is 0, hence the crash.
If you insist on using C functions, see: Safe Alternative to gets.
Otherwise lookup getline().