How to use mkl for FFT？

I am a new student in mkl and c language.

now when i replace FFT function with DftiComputeForward， i can not get the correct out put，why？

Realft(info.x,info.fftN);  // FFT info.x is  float in-out x[1] is real ,x[2] is complex.

  MKL_Complex8* x_cmplx = 0;
 x_cmplx = (MKL_Complex8*)mkl_malloc((info.fftN/2 + 1) * sizeof(MKL_Complex8), 64);
 DftiComputeForward(hand, info.x,x_cmplx);