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());

Answer 4

Yes, your expectation is wrong. std::string is meant to be different from C strings (e.g. not necessarily stored in consecutive memory / an array).

To duplicate the first section's behavior, try std::cout << b.c_str() instead of std::cout << b.

Answer 5

I expect std::string will behave identical to char array a.

Why? Nothing in the documentation, anywhere, having to do with std::string says it does this.

My suggestion, stop treating like C++ as C plus some stuff.