Structure packing in gcc

This is a quite common problem.It took some time for me to find out the solution.
gcc does not support the #pragma directives.
The __attribute__((packed)) of gcc helps you to do structure packing.It has to be added to the definition of each and every structure to be packed.

E.g:Here is a packed structure in which the field b is packed, so that it immediately follows a
struct data
{
char a;
int b;
}__attribute__((packed));

The attribute can be applied to the individual fields of a structure than applying it to entire structure as in this example

struct foo
{
char a;
int x[2] __attribute__ ((packed));
};

Related gcc warnings:
-Wpacked Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be misalignedfor little benefit. For instance, in this code, the variable f.x in structbar will be misaligned even though struct bar does not itself have the packed attribute:
struct foo
{
int x;
char a, b, c, d;
} __attribute__((packed));
struct bar
{
char z;
struct foo f;
};

-Wpadded Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller.

Just now came across another option in gcc

-fpack-struct

Packs all structure members together without holes.
Warning: the ‘-fpack-struct’ switch causes GCC to generate code that isnot binary compatible with code generated without that switch.

-Excerpts from the gcc3.3.2 documentation