Cout stack, operator <operator overload output Problem

In the output stream of cout in C ++, some problems are prone to errors. For example, the following simple program seems simple, but it is a question worth pondering ~~

# Include <iostream>

Using namespace STD;

Int Foo (Int & X)
{
Cout <"no." <x <"call" <"";
Return ++ X;
}

Int main ()
{
Int I = 1;
Cout <Foo (I) <'\ t' <Foo (I) <Endl;

}

At first, many people thought that the output results would be:

1st calls 2 2nd calls 3

But the result is:

1st calls 2nd calls 3 2

Why ??? The first thing you need to know is:

Process space:

Code zone -------------- stores Program Execution Code
Global data zone ------------ stores global data, constants, text volumes, static global volumes, and static local volumes.
Heap zone ---------------- stores dynamic memory for random application by the program
Stack zone ---------------- function data zone (local data zone)
(The above is the memory layout in the running state)


The entire function call process is the stack space operation process. When calling a function, C ++ does the following:
(1) Create the stack space of the called function, and its size is determined by the data volume in the function definition body;
(2) Protect the running status and return address of the called function;
(3) passing parameters;
(4) transfer control to the called function;
(5) After the function is run, copy the result to the bottom of the local data block of the function;
(6) restore the running status of the called function;
(7) return the call function.

Calling a function can be seen as a stack operation for the elements in a stack.

With the above introduction, you can understand the explanation process:

Original output statement: cout <Foo (I) <'\ t' <Foo (I) <Endl;

The execution sequence of cout output is from right to left. So:

1: Execute <Endl, because there is no STD: cout object, unable to execute, pressure Stack

2: Execute <Foo (I), execute Foo (1), output: 1st calls, get the return value 2, or because there is no STD: cout object, it cannot be output immediately, stack pressure
The Code becomes cout <Foo (I) <'\ t' <2 <Endl;

3: Execute <'\ t', without STD: cout object, cannot output immediately, press the stack
The Code becomes cout <Foo (I) <'\ t' <2 <Endl;

4: Execute <Foo (I), execute Foo (2), and output: 3 is returned for 2nd calls, or because no STD: cout object exists, it cannot be output immediately.
The Code becomes cout <3 <'\ t' <2 <Endl;

Pay attention to the following two points for the above process:

1. [Int & X] That is to say, X is actually the alias of I.

2. cout <Foo (I) <'\ t' <Foo (I) <Endl;
<==> Operator <(cout, Foo (I) return values, '\ t', Foo (I) return values, Endl ); the parameters are pushed to the stack area from right to left:

Cout stack, operator <operator overload output Problem