Function to create a vector of evenly spaced numbers in C++.

range.cc

// Create a vector of evenly spaced numbers.
vector<double> range(double min, double max, size_t N) {
    vector<double> range;
    double delta = (max-min)/double(N-1);
    for(int i=0; i<N; i++) {
        range.push_back(min + i*delta);
    }
    return range;
}

The performance difference is probably mainly due to initializing the vector to the correct size once and avoids the push_back() reallocation and copies when growing. Notice that the successive addition val += h accumulates error. After just a few iterations, the result will drift from min + i * delta from the original code.

Another version for 3D space (Unreal Engine API).

TArray<FVector> USplashComponent::distributeVectorsAcrossLine(FVector start, FVector end, int32 dens) const
{
	TArray<FVector> vectors;

	// safety check
	if (dens <= 0)
	{
		return vectors;
	}
	else
	{
		dens = FMath::Clamp(dens, 0, 500);
		FVector nextVector;

		for (int32 i = 0; i < dens + 1; i++)
		{
			nextVector.X = FMath::Lerp(start.X, end.X, (float)i / (float)dens);
			nextVector.Y = FMath::Lerp(start.Y, end.Y, (float)i / (float)dens);
			nextVector.Z = FMath::Lerp(start.Z, end.Z, (float)i / (float)dens);
			vectors.Add(nextVector);
		}
		return vectors;
	}
}