C++ Standard Library: string

Simple demo

In order to compile this demo, I had to specify the minimum standard (C++ 17): g++ -std=c++17 demo.cpp.

#include <string>
#include <string_view>
#include <iostream>


template<typename STR> void f(STR str) {

    STR         sub      = str.substr(4, 3);

    const char* addr_str = str.data();
    const char* addr_sub = sub.data();

    std::cout << "Difference between addresses: " << (addr_str - addr_sub) << std::endl;
    std::cout << sub.data() << std::endl;
}

int main() {

    std::string      digits  ("0123456789");

    f<const std::string     &>(digits);
    f<const std::string_view&>(digits);

}

Github repository about-cpp-standard-library, path: /string_view/demo.cpp

This simple demo program prints, when compiled and run on my computer:

Difference between addresses: 96
456
Difference between addresses: -4
456789

Thus, it demonstrates that std::string_view::substr() returns a view onto the string view on which substr() is called and the difference between their respective addresses is only 4.

Also, the char* returned by .data() is not null-terminated, thus, the rest of the original string is printed.

Conversely, if substr() is called on a std::string, it creates a new string, therefore, the difference between their addresses is larger than 4.

C++ Standard Library: string_view

Simple demo

See also