assign string to the string variable inside structure!

hi
simple question:(
its my code

Code:

---

#include <iostream>
#include <string>
using namespace std;
struct a{ 
 string test;
};
int  main()
{
a *b;
b->test="ds";
}

---

but the program stop working why?
and what can i do?
i dont want to use *char or sth else it must be string...

You have to allocate memory for the object.

Code:

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b=new a();

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Why use new at all?
Just

a b;
b.test = "ds";

will suffice.

Quote:

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Originally Posted by manasij7479

You have to allocate memory for the object.

Code:

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b=new a();

---

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Don't do that. This is better:

Code:

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#include<memory>
...

std::unique_ptr<a> b( new a() );

---

Although elisia's code is simpler, if it suffices.

Quote:

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Don't do that. This is better:

---

why ?
what doest this code mean?!!

Code:

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std::unique_ptr<a> b( newa() );

---

It makes the lifetime of the created object a() be the same as that of the pointer to a, called b. b is a unique_ptr, a type of smart pointer that will do that. This prevents your program from failing to delete the created object and leaking memory.

There are several smart pointers types, unique_ptr being for when you only need one pointer to the object that maintains ownership. The most versatile smart pointer is shared_ptr, which allows multiple pointers, and makes the object pointed to be destroyed when the last pointer is destroyed.

you mean if i use this
b=new a();
the object will remain in memory?
how about deleting that pointer?
delete b;
does it erase the object from memory??

Quote:

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Originally Posted by king_zart

you mean if i use this
b=new a();
the object will remain in memory?

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Yes, as long you don't delete it.
If that is not what you intend, either don't use pointers or use a smart pointer, as said by the others.

Quote:

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how about deleting that pointer?
delete b;
does it erase the object from memory??

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Yes.

Quote:

---

Originally Posted by king_zart

you mean if i use this
b=new a();
the object will remain in memory?
how about deleting that pointer?
delete b;
does it erase the object from memory??

---

Again, forget that delete exists. Don't use it.
Whenever you use new, use a smart pointer, and never ever worry about delete.

But you haven't explained why you are so eager to use new?

just one more question
i have this function
it make a link list that contain user name and password from a file(make_list(node)
then check_user_pass_equal(node,user,pass) function check that they are same or not

Code:

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int User_name_check()
{
  user_pass *node=new user_pass;
  std::cout<<"\nuser name : ";
  std::string user;
  std::getline(std::cin,user);
  std::cout<<"\nPassword : ";
  std::string pass;
  std::getline(std::cin,pass);
  make_list(node);
  int R=check_user_pass_equal(node,user,pass);
  if(R==1)
    make_directory(user);
  return R;


}

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does it remove the object and pointer after return R?
or i must add delete node; ?

Quote:

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Originally Posted by Elysia

Again, forget that delete exists. Don't use it.
Whenever you use new, use a smart pointer, and never ever worry about delete.

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That's somewhat extreme!

i use this

Code:

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std::unique_ptr<user_pass> node( new user_pass );

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in my User_name_check() function instead of new
but it doesnt compile...
error: 'unique_ptr' is not a member of 'std'|

Quote:

---

Originally Posted by king_zart

i use this

Code:

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std::unique_ptr<user_pass> node( new user_pass );

---

in my User_name_check() function instead of new
but it doesnt compile...
error: 'unique_ptr' is not a member of 'std'|

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#include<memory>

Quote:

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Originally Posted by manasij7479

#include<memory>

---

i do that before posting...
i am using codeblock v10.05

Code:

---

#include <iostream>
#include<memory>
using namespace std;
struct a{
 string test;
};
int  main()
{
unique_ptr<a> b( new a() );
}

---

error: 'unique_ptr' was not declared in this scope|
error: expected primary-expression before '>' token|
error: 'b' was not declared in this scope|

there is some problem with codeblock right?!!
even i get these error when i try to compile example in this site!!
std::unique_ptr - cppreference.com
is it c++11 code ?
how can i use it in codeblock?!!!!!