动态查找结构的大小

Question

Is there any way to find the structure size dynamically in C??

Sizeof is compile time operator.. so what's the other option.

If we can have dynamically allocated array(flexible arrays) in a structure, then finding the structure size dynamically should also be there.. Plz help me out...

Answer 1

当您在C中动态分配数组时，如果您想知道数组的大小，还必须记住它的大小！

Answer 2

Structure sizes must be known at compile-time.

If it contains a pointer to dynamically allocated memory then that memory is not part of the struct - it's outside the struct and the pointer is pointing at it - so it does not affect the sizeof the struct.

If you're talking about flexible array member then you will need to implement your own way of knowing how much memory you allocated, eg have a struct member variable that holds the size.

Answer 3

sizeof 's results are compile time constant as a the size of a variable or structure does not change during run-time.

The only exception to this are V(ariable)L(ength)Arrays for which the code defnding them "knows" the size.

Referring:

we can have dynamically allocated array in a structure

So let's assume:

struct s
{
  size_t size;
  int * ints;
}

The size is sizeof(struct s) . That is the sum of

• the size of an unsigned interger: sizeof(size_t)
• the size of a pointer to int : sizeof (int *)
• some optional padding bytes

This is independed of to how many bytes the structure's member int * ints may point.