Geek asks and answers

Why does C ++ Standard 1.9 / 5 talk about "possible execution sequences"?

According to C ++ 03 Standard 1.9 / 5

The corresponding implementation, executing a well-formed program, should provide the same observable behavior as one of the possible sequences of execution of the corresponding instance of an abstract machine with the same program and the same input.

I do not get "like one of."

If I have a specific program and a specific input, and my program does not contain undefined behavior, why can the observed behavior change? What is meant by “one possible execution sequence”?

+5
source share
4 answers

Consider:

x = f() + g();

:

__temp1 = f();           /*or*/     __temp1 = g();
__temp2 = g();           /*or*/     __temp2 = f();
x = __temp1 + __temp2;   /*or*/     x = __temp2 + __temp1;

, ; , . f() g() , .

+8

++ . ,

int x = f(a) + f(b);

f (a) f (b).

+12

++ . , :

    proc( a(), b() );

a(), b() proc(), a() b(). , , a() b() (, ), , .

( . , ).

+3

, , , , ++ 11 , .

, , " A" " B", , , . " A", " B", , ( ).

+2

More articles:


All Articles