c - gcc compiler is not allocating memory contigously -

i writing simple program, after declaring variables checking addresses of variables memory not allocated contiguously there gaps in between. here program. why leaving gaps not understanding

#include < stdio.h > #include < stdint.h >  int main() {          char char_one,char_two;         int = 5,b = 7,*ptr,*ptr_one;         static  int *sum_ptr;         printf("address   of               %u\n",&a);         printf("address  of variable b       %u\n",&b);         printf("address  of ptr variable     %u\n",&ptr);         printf("address  of ptr_one variable %u\n",&ptr_one);         printf("address of char_one var      %u\n",&char_one);         printf("address of char_two var      %u\n",&char_two);         return 0; } 

output: address of 2636128020

address of variable b 2636128024

address of ptr variable 2636128000

address of ptr_one variable 2636128008

address of char_one var 2636128030

address of char_two var 2636128031

the c standard not require memory variables allocated contiguously. in fact, memory might not allocated @ if compiler decides can optimize keeping value in register instead.

if declare struct, contents of struct ordered way declare them, still might need consider how data aligned within struct - example, ints aligned on 4-byte boundaries in many architectures. if have:

struct foo {     char a;     int b; } 

a guaranteed come before b in memory, still padded bytes between them keep correct alignment (so takes 8 bytes store struct, though "really" needs 5).

here's resource how structure alignment works:

the lost art of c structure packing