C++ :: Writing In Binary Format Array Of Unsigned Int Values

I am trying to write down in binary format an array of unsigned int values but i get the following compilation error :

: In function ‘int CIndex(std::fstream&, std::fstream&, std::fstream&, std::fstream&)’:
./src/IndexBuilder/index.cpp:23:26: error: no matching function for call to ‘std::basic_fstream<char>::write(int*, long unsigned int)’
./src/IndexBuilder/index.cpp:23:26: note: candidate is:
/usr/include/c++/4.6/bits/ostream.tcc:184:5: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*, std::streamsize) [with _CharT = char, _Traits = std::char_traits<char>, std::streamsize = long int]

This is the part the is not working:

Code:
// uia is : unsigned int * uia;
// then I have allocated the space for it
// load it with unsigned int's
// k is the number of variables in my array

o.write(uia,sizeof(unsigned int)*k); But thsi should be so simple and strait forward.... in c i do it as :

Code:
fwrite(uia, sizeof(unsigned int), k , fp); but since i would need to convert fstream to FILE* i decided to do it c++ way.

and this is how i opened the file :

Code:
o.open (fileName.c_str(),std::ios::out|std::ios::binary);