c++ new/delete and char *

Question

Can anyone help me, why I\'m getting an error message while trying to free the allocated memory: Heap corruption detected. CTR detected the application wrote the memory after en

Answer 1

char *s = new char [5];
strcpy(s, "hello");

Causes Undefined behavior(UB).
You are writing beyond the bounds of allocated memery. You allocated enough memory for 5 characters but your string has 6 characters including the \0.

Once your program has caused this UB, all bets are off and any behavior is possible.

You need:

char *s = new char [strlen("hello") + 1];

In fact the ideal solution is to use std::string and not char *. These are precisley the mistakes which std::string avoids. And there is no real need of using char * instead of std::string in your example.
With std::string:

• You don't need to new anything
• You don't need to delete anything &
• You can do everything with std::string, that you do with char *.

Answer 2

All answers so far have addressed either the first or the second allocation. To sum up, there are two changes you must make:

char *s1 = new char [strlen(s) + 1];
...
char *s = new char [5 + 1];

In both cases, you must allocate enough space for the string plus one byte for the terminating '\0'.

As others already pointed out, with c++ it's easier and safer to use std::string. No fuss with allocation and release of memory or paying attention to '\0' bytes:

std::string ff (const std::string &s){
    std::string s1(s);
    // do something else with s1
    return s1;
}

int main(int argc, char* argv[])
{
    std::string s("hello");
    std::string s2 = ff(s);
    return 0;
}

and if it's just copying the string:

std::string s("hello");
std::string s2(s);