A way to find the size and location of padding in a struct?

Question

I\'m trying to write a tool that will take as input some C code containing structs. It will compile the code, then find and output the size and offset of any padding the com

Answer 1

You could use Exuberant Ctags to parse your source files instead of using a CPAN module or hacking something up yourself. For instance, for the following code:

typedef struct _foo {
    int a;
    int b;
} foo;

ctags emits the following:

_foo    x.c     /^typedef struct _foo {$/;"     s                               file:
a       x.c     /^    int a;$/;"                m       struct:_foo             file:
b       x.c     /^    int b;$/;"                m       struct:_foo             file:
foo     x.c     /^} foo;$/;"                    t       typeref:struct:_foo     file:

The first, fourth, and fifth columns should be enough for you to determine what struct types exist and what their members are. You could use that information to generate a C program that determines how much padding each struct type has.