The C struct has unsigned longs mostly. Each of these is 32 bytes, right?
I would not bet on that. The C99 standard defines int as having the natural size suggested by the architecture of the execution environment (large enough to contain any value in the range INT_MIN to INT_MAX as defined in the header <limits.h>)., so an int needs at least 16 bits. Other integer types, including unsigned long, are definied similary. C requires a minimum range, but no fixed number of bits. The implementation may choose bit sizes as required by the machine. So most C compilers on 32 bit systems actually define int as a 32 bit number, long int is typically 32 or 64 bit. But if you run on a 36 bit architecture without a 32 bit emulation layer, int should use 36 bit, long int may use 72 bit, and long long int could use 144 bit. Things get more complicated on 64 bit systems that attempt to support 32 bit software, see http://en.wikipedia.org/wiki/64-bit_computing#64-bit_data_models. Note that UNICOS defines all basic integer types as 64 bit.
See also http://stackoverflow.com/questions/589575/size-of-int-long-etc, http://en.wikipedia.org/wiki/C_data_types.
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)