Why setting null in the middle of std string doesn't have any effect

Question

Consider

#include <string>
#include <iostream>

int main()
{
    /*
    hello
    5
    hel
    3
    */
    char a[] = "hello";
    std::cout << a << std::endl;
    std::cout << strlen(a) << std::endl;
    a[3] = 0;
    std::cout << a << std::endl;
    std::cout << strlen(a) << std::endl;

    /*
    hello
    5
    hel o
    5
    */
    std::string b = "hello";
    std::cout << b << std::endl;
    std::cout << b.length() << std::endl;
    b[3] = 0;
    std::cout << b << std::endl;
    std::cout << b.length() << std::endl;

    getchar();

}

I expect std::string will behave identical to char array a. That's it, insert null character in the middle of the string, will "terminate" the string. However, it is not the case. Is my expectation wrong?

Answer 1

A std::string is not like a usual C string, and can contain embedded NUL characters without problems. However, if you do this you will notice the string is prematurely terminated if you use the .c_str() function to return a const char *.

Answer 2

No - std::strings are not NUL-terminated like C "strings"; the std::string records its length independently.

Answer 3

@Lou is right: don't do that. Instead, do this:

b.erase (3, b.length());