Deleting char* after assigning it to a string variable

Question

I have executed the below code and it works perfectly. Since it is about pointers, I just want to be sure. Though I\'m sure that assigning char* to string makes a copy and even

Answer 1

There is no problem, as long as newChar points to a null-terminated string, and is not null itself.

std::string has constructor that allows an implicit construction from a const char*. It makes a copy of the character string represented by the input const char * so it works under the assumption that the char* is a null terminated string, since there is no other way to know how many characters to copy into the string's own data storage. Furthermore, a NULL pointer is actually disallowed by the standard.

Answer 2

No, because std::string copies the contents of your char*, so you're free to delete it when you no longer need it.

Answer 3

The code is fine, if you look at the constructors of std::basic_string here you'll be able to deduce that std::string has two interesting constructors here:

(4) string(char const*,
           size_type count,
           Allocator const& alloc = Allocator() );

(5) string(char const* s,
           Allocator const& alloc = Allocator() );

Both perform a copy, and the first reads exactly count characters whilst the second reads up until it encounters a NUL-character.

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That being said, I actively encourage you not to use dynamic allocation here. If you want a temporary buffer to play with, consider using std::vector instead.

#include <stdio.h>
#include <string.h>
#include <string>
#include <iostream>

int main()
{
    std::string testStr = "whats up ...";
    unsigned strlen = testStr.length();

    std::vector<char> buffer(strlen+1);

    memset(&buffer[0],'\0',strlen+1);
    memcpy(&buffer[0], testStr.c_str(), strlen);

    std::cout << "  :11111111   :   " << &buffer[0] << "\n";

    std::string newStr(&buffer[0]);

    std::cout << "  2222222 : " << newStr << "\n";

    buffer.clear();

    std::cout << "  3333333 : " << newStr << "\n";
}

Note: both vector and string have range-constructors, to build them from a range of iterators, that I purposefully refrained from using to avoid confusion and you being overwhelmed. Just know that you could have used them to avoid calling memcpy and risking a buffer overflow though.