Does standard C++11 guarantee that temporary objec

问题:

Does standard C++11 guarantee that all 3 temporary objects have been created before the beginning performe the function?

Even if temporary object passed as:

1. object
2. rvalue-reference
3. passed only member of temporary object

http://ideone.com/EV0hSP

#include <iostream>
using namespace std;

struct T { 
    T() { std::cout << "T created \n"; }
    int val = 0;
    ~T() { std::cout << "T destroyed \n"; }
};

void function(T t_obj, T &&t, int &&val) {
    std::cout << "func-start \n";
    std::cout << t_obj.val << ", " << t.val << ", " << val << std::endl;
    std::cout << "func-end \n";
}

int main() {

    function(T(), T(), T().val);

    return 0;
}

Output:

T created 
T created 
T created 
func-start 
0, 0, 0
func-end 
T destroyed 
T destroyed 
T destroyed 

Working Draft, Standard for Programming Language C++ 2016-07-12: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf

§ 5.2.2 Function call

§ 5.2.2

1 A function call is a postfix expression followed by parentheses containing a possibly empty, comma-separated list of initializer-clauses which constitute the arguments to the function.

But can be any of T created after func-start?

Or is there any way to pass arguments as g/r/l/x/pr-value so that the function started before the temporary object be created?

回答1:

[intro.execution]/16:

When calling a function (whether or not the function is inline), every value computation and side effect associated with any argument expression, or with the postfix expression designating the called function, is sequenced before execution of every expression or statement in the body of the called function.

回答2:

From [expr.call]/8 we have

[ Note: The evaluations of the postfix expression and of the arguments are all unsequenced relative to one another. All side effects of argument evaluations are sequenced before the function is entered (see 1.9). —end note ]

This means that all parameters are constructed before the function is entered.

Consequently this also guarantees that all parameters are destroyed after the function exits.