About FFT function:performFrequencyOnlyForwardTransform (fftData)?

Hi everyone,
Suppose that a FFT object has been defined and the fifo array stores 1024 time domain signal points. The first 1024 elements of fftData array are the same as the fifo array and the last 1024 elements of fftData array are all zeros:
dsp::FFT forwardFFT(10);
float fifo [1024];
float fftData [2048];
After the call of function performFrequencyOnlyForwardTransform (fftData): FFT.performFrequencyOnlyForwardTransform (fftData), what contents of each fftData array element? is each element’s value represents a frequency component’s magnitude? If so,what is that magnitude’s corresponding frequency value?

Best regards!

How should we choose the “order” parameter when we create a FFT object? Is that important?

FFT (int order);

Here all the time domain signal points are all real number, not complex number.

Yes, it determines the size of your FFT:

The number of points the FFT will operate on will be 2 ^ order.

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Regarding the frequency question:
f = sampleRate * bin / fftSize
with bin ∈ [0; fftSize-1]

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