C + + Standard: C + + does not allow temporary values to be modified for any basic type (including pointers)

From the C + + standard library, see this sentence: C + + does not allow the modification of any basic type (including pointers) of the temporary value, think for a long time, really do not understand. Basic type Char,int,float and so on, what's the temporary value? For example, int a=2, what is the temporary value of this a? Can I interpret 2 as a temporary value? If 2 is a temporary value, obviously not, because you can't change the 2, then that sentence is meaningless. Temporary value first regardless, do not know how to find, search a lot, understand a general meaning, first look at a few examples from the Internet to find:

#include <iostream>usingnamespace  std; void Main () {    int4;    A5;     int *b;     4 ;     5 ;}

a++;
Suffix + + Returns a (temporary) rvalue whose value is the original value of a, and cannot be assigned a value. (Note that this is said to be the right value)
*b++ = 5;
The expression is * (b++) = 5;
This means adding 1 to the pointer before referencing.
b++, like a++, is a temporary right-hand value (whose value is the original value of B) and cannot be assigned, such as the following code is not valid:
b++ = ptr;
The b++ expression produces a temporary pointer value that, after the pointer is dereferenced (of course, the value must point to a valid location), is an lvalue , so:
*b++ = 5; is legal.

Look again at an example;

#include <iostream>using namespacestd;classmy{ Public: My (intj=0): I (j) {}inti; void operator= (my& out)//Here we redefine an assignment operator =, to prepare for the assignment below. {i= out. I; }}; My fun () {My temp (1); returnTemp//This returns a temporary variable for a class} intfun2 () {intA; returnA//this returns a normal int temporary variable }intMain () {my out(2); Fun ()= out;//Here you can assign a value to a temporary variable of a classFun2 () =3;//But here's an error for a variable of the normal int type.}

FUN2 () returns an rvalue that cannot be assigned, and can only be interpreted as such.

Then look at the issues mentioned in the C + + standard library:

vector<int> coll;.....sort (++coll.begin (), Coll.end ());

The book says it will fail to compile. I compiled it under VS2012 without problems.

Remember one point: the right value cannot be modified.

C + + Standard: C + + does not allow temporary values to be modified for any basic type (including pointers)