Real input to FFTW - c++

Question

When I use FFTW, specifically the plan creation function fftw_plan_dft_r2c_1d(), for purely real input, the only "planner flag" (FFTW's terminology) which works is FFTW_ESTIMATE. Any of the others which I try, viz., FFTW_EXHAUSTIVE, FFTW_MEASURE, and FFTW_PATIENT, all generate an output file with all zeros.
I have tried changing the number of input data items from powers of 2 to otherwise. That makes no difference.
Scilab uses FFTW for its fft() and thus I am able to compare the output from my C++ program with the output from Scilab for the same input data file. When I use FFTW_ESTIMATE the two outputs match.
I have read the FFTW documentation. I cannot determine why the other planner flags do not work.
I am interested in using the FFTW_MEASURE planner flag since once the plan is formulated, I will want to use it repeatedly.
Below is my code. I have not included the fftw3.h file as I have not made any changes to it.
#pragma once
// FFT_05.h
//#include <array>
#include <cmath>
#include <complex>
#include <cstdint>
#include <fstream>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include "fftw3.h"
#define M_PI 3.14159265358979323846
// FFT_05_c.cpp
#include "FFT_05.h"
//*****************************************************************************
int32_t main(int argc, char* argv[]) {
std::fstream data_File;
std::string directory = "C:/Documents/Visual Studio 2022/Projects/";
directory += "FFT_05/Scilab programs/02/";
std::string file_Name = "Time_domain_input.txt";
data_File.open(directory + file_Name, std::ios_base::in | std::ios_base::binary);
double input_Value = 0.0;
int data_Count = 0;
if (data_File.is_open()) {
while (!data_File.eof()) {
data_File >> input_Value;
data_Count++;
}
}
std::cout << data_Count << std::endl;
data_File.seekg(0, std::ios_base::beg);
double* in;
fftw_complex* out;
fftw_plan p;
in = (double*)fftw_malloc(sizeof(double) * data_Count);
int data_Count_Out = (data_Count / 2) + 1;
out = (fftw_complex*)fftw_malloc(sizeof(fftw_complex) * data_Count_Out);
int i = 0;
while (!data_File.eof()) {
data_File >> input_Value;
in[i++] = input_Value;
}
data_File.close();
//for (int i = 0; i < data_Count; i++) {
// //std::cout << in[i][0] << ", " << in[i][1] << std::endl;
// std::cout << (i + 1) << ". " << in[i] << std::endl;
//}
//std::cout << "\n\n";
// FFTW procedure
p = fftw_plan_dft_r2c_1d(data_Count, in, out, FFTW_ESTIMATE);
if (!p) {
std::cout << "FFTW plan is NULL\n";
exit(1);
}
fftw_execute(p);
fftw_destroy_plan(p);
std::fstream FFT_Data_File;
FFT_Data_File.open(directory + "frequency_Domain_File_Name_c.txt",
std::ios_base::out | std::ios_base::binary | std::ios_base::trunc);
for (int i = 0; i < (data_Count_Out - 1); i++) {
FFT_Data_File << out[i][0] << " " << out[i][1] << std::endl;
}
FFT_Data_File << out[(data_Count_Out - 1)][0] << " " << out[(data_Count_Out - 1)][1];
FFT_Data_File.close();
fftw_free(in);
fftw_free(out);
}