write string to pointer C++

Question

I have a Dll which I inject into my target process. This Dll changes some variables at give memory addresses. Normaly I do it like:

  int* variable = (int*)0x????????;
  *variable = 1;

Now I want to do the same thing with a string. Reading the string works.

string* variable = (string*) 0x????????;

But changing the string crashes the process.

*variable = "hello world"; //crash

How can I fix this?

This is extremely dodgy. You can sort of hack it for simple, built-in types, but a `std::string` is no such thing. It contains pointers to data and you're not handling that. What on earth are you actually trying to accomplish? — Lightness Races in Orbit, Dec 30 '15 at 14:31
Where do you get that address from? Why do you think there is properly constructed object at that address? — Slava, Dec 30 '15 at 14:33
No, that's _how_ you're trying to accomplish it. _What_ are you trying to accomplish? — Lightness Races in Orbit, Dec 30 '15 at 14:34
_"I read it before to check"_ That is not a valid check. Where did the address come from? — Lightness Races in Orbit, Dec 30 '15 at 14:35
It displays the right string if I use `sprintf();` I try to hack a game (change player name) — nice, Dec 30 '15 at 14:36
I mean you have to basically use poor C, no C++ objects for such hacks. `std::string` is an object. — Slava, Dec 30 '15 at 14:40

score 0 · Answer 1 · answered Dec 30 '15 at 14:40

You have not shown how you guarantee that the memory at the address 0x???????? is allocated properly or that the string object is initialized.

If the pointer does not point to allocated memory, or if the string is not initialized when you copy-assign it, then you get undefined behaviour. Possible undefined behaviour include:

But changing the string crashes the process.

To fix it, allocate and initialize a string object and use the address of that string.

score 0 · Accepted Answer · edited May 23 '17 at 12:04

0

You cannot use std::string or any other non POD data type this way. What you need to do instead:

 char* variable = (char*) 0x????????;
 strcpy( variable, "hello world" );

or other, maybe MS specific functions to manipulate C strings.

edited May 23 '17 at 12:04

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answered Dec 30 '15 at 14:44

Slava

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write string to pointer C++

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