Why freeing invalid left pointers undefined in C ++?

Question

Consider the following program:

#include <iostream>
int main()
{
    int b=3;
    int* a=&b;
    std::cout<<*a<<'\n';
    delete a;  // oops disaster at runtime undefined behavior
}

Well, the behavior of the program is undefined according to the C ++ standard. But my question is, why is it left undefined? Why do C ++ implementations not give compiler errors or any warnings? Is it really difficult to determine the correctness of a pointer (does it mean to check if the pointer is returned new at compile time?) Is there any overhead to determine if the pointer is statically valid (i.e. compile time)?

Answer 1

, , , :

volatile bool newAlloc;

int main()
{
   int b=3;
   int* a;
   if(newAlloc)
   {
       a = new int;
   } else {
       a = &b;
   }
   std::cout<<*a<<'\n';
   delete a;  // impossible to know what a will be
}

Answer 2

, , . , , , , , .

undefined, , , , .

Answer 3

++ - ?

Clang .

:

$ scan-build clang++ main.cpp
scan-build: Using '/usr/bin/clang' for static analysis
main.cpp:7:5: warning: Argument to 'delete' is the address of the local variable 'b', which is not memory allocated by 'new'
    delete a;  // oops disaster at runtime undefined behavior
    ^~~~~~~~
1 warning generated.
scan-build: 1 bug found.

, , , Static Analyzer .

Answer 4

:

new/delete , new, . . , delete , . , , delete , . , - undefined.

, , ?
new/delete , . - . , ; , .

, / , ++ .