不是的。

string f(bool x)
{
    string s = "1111111111111111111111111111111111111111111111111111111111111";
    if(x){
        std::cout << "var address: " << &s << std::endl;
        std::cout << "buf address: " << (void *)(s.data()) << std::endl;
        return s;
    }
    return string("222222222222222222222222222222222222222222222222222222222222222");
}

string g(bool x)
{
    const string s = "1111111111111111111111111111111111111111111111111111111111111";
    if(x){
        std::cout << "var address: " << &s << std::endl;
        std::cout << "buf address: " << (void *)(s.data()) << std::endl;
        return s;
    }
    return string("222222222222222222222222222222222222222222222222222222222222222");
}

string r()
{
    const string s = "1111111111111111111111111111111111111111111111111111111111111";
    std::cout << "var address: " << &s << std::endl;
    std::cout << "buf address: " << (void *)(s.data()) << std::endl;
    return s;
}

int main()
{
    {
        std::cout << "call f(true), expect move ctor" << std::endl;
        string s = f(true);

        std::cout << "var address: " << &s << std::endl;
        std::cout << "buf address: " << (void *)(s.data()) << std::endl;
    }

    std::cout << "===============" << std::endl;
    {
        std::cout << "call g(true), expect copy ctor" << std::endl;
        string s = g(true);

        std::cout << "var address: " << &s << std::endl;
        std::cout << "buf address: " << (void *)(s.data()) << std::endl;
    }

    std::cout << "===============" << std::endl;

    {
        std::cout << "call r(), expect NRVO" << std::endl;
        string s = r();

        std::cout << "var address: " << &s << std::endl;
        std::cout << "buf address: " << (void *)(s.data()) << std::endl;
    }

    return 0;
}

$ g++ t.cpp -std=c++17

输出：

call f(true), expect move ctor
var address: 0x7fffc4ea36c0
buf address: 0x7fffbd418280
var address: 0x7fffc4ea3720
buf address: 0x7fffbd418280
===============
call g(true), expect copy ctor
var address: 0x7fffc4ea36c0
buf address: 0x7fffbd418280
var address: 0x7fffc4ea3720
buf address: 0x7fffbd4182d0
===============
call r(), expect NRVO
var address: 0x7fffc4ea3720
buf address: 0x7fffbd4182d0
var address: 0x7fffc4ea3720
buf address: 0x7fffbd4182d0

case-5对应的是g(true)，你可以看到变量和buf地址都不一样。

【 在 libgcc 的大作中提到: 】
: 为什么我试了下case5是move的?
: string的data()返回的地址是一样的
:
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