The size of "program design" C and C + + hollow structure and empty class

Today encountered a pen question, asked what is the size of the C + + empty class is what, with the program tested a bit.

#include <iostream>using namespace Std;class ClassA {};//struct STRUCTA {////};int main () {  cout << "C LassA "<< sizeof (ClassA) << Endl;}

The output result is 1;

Expands on how space in C and C + + is occupied by an empty class followed by an empty struct.

In C + +, each time a class or struct is defined, the compiler assigns it at least 1 bytes of memory by default, guaranteeing that it has its corresponding location in memory , so that once the class or struct is instantiated, it will not cause an error because the memory cannot be found.

#include <iostream>using namespace Std;class ClassA {};struct structa {};int main () {ClassA a;struct structa b;cout << "ClassA" << sizeof (ClassA) << endl;cout << "a" << sizeof (a) << endl;cout << ; "Structa" << sizeof (STRUCTA) << endl;cout << "B" << sizeof (b) << Endl;}

Results:

Obviously, in C + +, the existence of an empty class and an empty struct is allowed, and both allow instantiation (no compilation errors).

Instead. There are no classes in C, only structs, and when you define a struct, the C language does not intelligently allocate memory for it, so the empty struct does not exist in C.

(VC6.0 is compiled but this is related to compilers)

This article was written by Cout_sev.

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The size of "program design" C and C + + hollow structure and empty class