Difference in methods for converting std string to char*

I know there are a ton questions on how to convert a std::string to a char* and through my research, I have adopted a few different options. However, the only one that seems to work for me is const_cast from the c_str() method.

So I am using that for now, but would like to know more information as to why the other methods do not work. What am I missing in my understanding as to why this isn't working as intended which seems to work for many others.

#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()
{
    char* test = "Hello World";
    string testStr(test);

    vector<char> testVec2(testStr.begin(), testStr.end());
    // testVec2[0] = 'F';
    char* test2 = reinterpret_cast<char*>(testVec2.data());

    vector<char> testVec3(testStr.begin(), testStr.end());
    // testVec3[0] = 'G'; 
    char* test3 = &testVec3[0];

    // The only one that works
    char* test4 = const_cast<char*>(testStr.c_str());

    cout << "char* test: " << test << " [" << strlen(test) << "]" << endl;
    cout << "str test: " << testStr << " [" << testStr.length() << "]" <<     endl;
    cout << "=== conv testing === " << endl;
    cout << "char* test2: " << test2 << " [" << strlen(test2) << "]" <<     endl;
    cout << "char* test3: " << test3 << " [" << strlen(test3) << "]" << endl;
    cout << "char* test4: " << test4 << " [" << strlen(test4) << "]" << endl;

    cin.get();
    return 0;
}

I know the pitfalls of using const_cast but it works for my situation at the moment. I simply take the string from the user, pass it to a C API and do nothing else with it (no worries of it being modified).

Here is a sample of the output https://i.sstatic.net/TaiC8.jpg

So what am I doing wrong and is there a better way to do this?

---

UPDATE Thanks to everyone for the extremely fast answers. It seems that my underlying confusion was the assumption of the null terminating character not being in the new buffer that I was assigning to the char* variable. Hence why my output was showing random characters after the string (that should have been my clue but it has been so long since I've done C/C++)

I also should have tagged this C++17 originally (since fixed) as that is what I am aiming for. I did not have that enabled in my console app in Visual Studio which made the solution by Passer By below work. That is the method I will use going forward.

Bottom line, changing my target to C++17 this works as expected

char* test = "Hello World";
string testStr(test);
vector<char> testVec2(testStr.begin(), testStr.end());  
char* test2 = testStr.data();

vector<char> testVec2(testStr.begin(), testStr.end());

this will create the following vector:

vector<char> testVec2 = {'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd'};

Anything jumps at you from that? It should. It doesn't contain the null terminator character. Any attempt to use testVec2.data() as a C string will result in Undefined Behavior because of this.

Although from C++11 std::string's underlying buffer has to contain the null terminator character, the begin - end range doesn't include it.