'std::vector<double>::iterator' has no member named 'begin' - c++

Question

So I am trying to perform recursion ( A very simple code for split radix recursive butterflies) on a large C++ STL vector and I am using iterators to call the recursion but it isn't working as I keep getting errors.
#include <iostream>
#include <cmath>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
template <typename T>
class fft_data{
public:
vector<T> re;
vector<T> im;
};
void inline split_radix_rec(vector<double>::iterator r,vector<double>::iterator i, int sgn,int N) {
if (N == 1) {
return;
} else if (N == 2) {
for (int k = 0; k < N/2; k++) {
int index = 2*k;
int index1 = index+1;
double taur = *(r+index1);
double taui = *(i+index1);
*(r+index1) = *(r+index) - taur;
*(i+index1) = *(i+index) - taui;
*(r+index) = *(r+index) + taur;
*(i+index) = *(i+index) + taui;
}
N=N/2;
} else {
int m = N/2;
int p = N/4;
double PI2 = 6.28318530717958647692528676655900577;
double theta = -1.0 * sgn * PI2/N;
double S = sin(theta);
double C = cos(theta);
double PI6 = 3.0*6.28318530717958647692528676655900577;
double theta3 = -1.0 * sgn * PI6/N;
double S3 = sin(theta3);
double C3 = cos(theta3);
double wlr = 1.0;
double wli = 0.0;
//T wl2r = (T) 1.0;
//T wl2i = (T) 0.0;
double wl3r = 1.0;
double wl3i = 0.0;
double tau1r,tau1i,tau2r,tau2i;
double ur,ui,vr,vi;
for (int j = 0; j < p; j++) {
int index1 = j+m;
int index2 = index1+p;
int index3 = j+p;
tau1r = *(r+index1);
tau1i = *(i+index1);
tau2r = *(r+index2);
tau2i = *(i+index2);
ur = tau1r + tau2r;
ui = tau1i + tau2i;
vr = sgn* (tau2r - tau1r);
vi = sgn* (tau2i - tau1i);
*(r+index2) = *(r+index3) - vi;
*(i+index2) = *(i+index3) + vr;
*(r+index1) = *(r+j) - ur;
*(i+index1) = *(i+j) - ui;
*(r+index3) = *(r+index3) + vi;
*(i+index3) = *(i+index3) - vr;
*(r+j) = *(r+j) + ur;
*(i+j) = *(i+j) + ui;
}
split_radix_rec(r.begin(),i.begin(),sgn,m);
split_radix_rec(r.begin()+m,i.begin()+m,sgn,p);
split_radix_rec(r.begin()+m+p,i.begin()+m+p,sgn,p);
}
}
int main() {
vector<double> u,v;
for (int i = 0; i < 256; i++) {
u.push_back(i);
v.push_back(i);
}
int sgn = 1;
int N = 256;
split_radix_rec(u.begin(),v.begin(),sgn,N);
return 0;
}
Here are the errors I am getting
main.cpp:93:21: error: 'std::vector<double>::iterator' has no member named 'begin'
6 Identical errors on lines 93,94,95 (the three split_radix_rec() functions called from within the split_radix_rec function). This is part of a much larger code so I want it to work for STL vectors. What am I doing wrong?

Answer 1

As the error states, you are calling begin() on a std::vector<double>::iterator.
You should call that on a std::vector<double>, so that it could return you a std::vector<double>::iterator.

Answer 2

r,i are itself iterators(begins) in your code.
Try:
split_radix_rec(r,i,sgn,m);
split_radix_rec(r+m,i+m,sgn,p);
split_radix_rec(r+m+p,i+m+p,sgn,p);

Answer 3

There is way too much code to give you a concise answer, but the error clearly states that you are calling begin() on a vector iterator instead of a vector. And that happens at the split_radix_rec recursive call. You may have intended this instead:
split_radix_rec(r,i,sgn,m);
split_radix_rec(r+m,i+m,sgn,p);
split_radix_rec(r+m+p,i+m+p,sgn,p);