Question

language is C with gcc compiler

if i make a struct like so

struct test {

    char item_1[2];
    char item_3[4];
    char item_4[2];
    char item_5[2];
    char item_6[4];

};

and i do a sizeof(struct test) it returns 14(bytes). which is the expected result.

but if i do

struct test {

    int16_t item_1;
    int32_t item_3;
    int16_t item_4;
    int16_t item_5;
    int32_t item_6;

};

sizeof(struct test) will return something strange like 44. when i debug using gnu ddd i can see inside the structure and see that it all looks normal and all items have the expected number of bytes.

so why is the sizeof operator returning a unexpected value ?

Answer 1

Compilers may insert padding between struct members, or after the last member. This is normally done to satisfy alignment requirements. For example, an int32_t object might require 4-byte alignment, so the compiler inserts 2 bytes of padding between the first and second members. The details will vary depending on the platform.