want to write only real data from cufftDoubleComplex variable

Hello Everyone,
I am using cuFFT Library. I am performing cufftExecZ2Z transformation.
I want to write only real data from my cufftDoubleComplex variable.
My data is around 2GB so i dont want to write complex part in my file. Dont suggest loops!
I am using fwrite function to do it. fwrite(arrayOfDoubleComplex,2nxnynzsizeof(double),1,fp);

Suggest me methods by which i can write only real data. Also suggest if u know some other file writing techniques which are more faster.

Thank You For response in advance.