"vector" was not declared in this scope

Question

I got this error ,,"vector" was not declared in this scope'' for the following code when I separate in *h and *cpp a file This is the main.cpp:

#include <iostream>
#include <math.h>
#include <vector>
#include "functia.h"

using namespace std;

int main()
 {
  vector<double> s(3);
  double b= 4;
  fun(s, b);
  cout<<s[0]<<endl;
  double c= 9;
  fun(s, c);
  cout<<s[0];

  }

functia.h:

 void fun(vector<double> & rS, double a)
 {
   rS[0] = a + 3;
   rS[1] = 4;
   rS[2] = 5;
 }

functia.cpp:

#include <iostream>
#include <math.h>
#include<vector>

using namespace std;


void fun(vector<double> &, double );

Why does you _.cpp_ contain the declaration and you _.h_ file the definition of `fun(...)`? Something seems odd there. — muXXmit2X, Mar 15 '17 at 11:30
This is how I learned: in .cpp the declaration and in .h the definition. It is working in that way for files without ,,vector''. — Mihaela, Mar 15 '17 at 11:33
Lots of bugs in code, its not just vector error, solve other bugs vector won't be issue. — SHAHS, Mar 15 '17 at 11:37
@MIhaela, As soon as two files include the same header, you violate the One Definition Rule. — chris, Mar 15 '17 at 11:39
_"This is how I learned: in .cpp the declaration and in .h the definition"_ That is backwards. — Lightness Races in Orbit, Mar 15 '17 at 12:29

score 14 · Accepted Answer · edited May 23 '17 at 10:29

You've got the declaration in the cpp file and the definition in the header, it should really be the other way round.

After you've swapped the files round remove using namespace std; from functia.h as it's not good practice to pull in namespaces in header files. You'll need to change the declaration to

void fun(std::vector<double> &, double );

See "using namespace" in c++ headers

I'd also strongly recommend reading C/C++ include file order/best practices

score 0 · Answer 2 · answered May 11 '23 at 14:59

0

Change "vector" to "std::vector"

answered May 11 '23 at 14:59

Alexej Vasko

1

This does not provide an answer to the question. Once you have sufficient [reputation](https://stackoverflow.com/help/whats-reputation) you will be able to [comment on any post](https://stackoverflow.com/help/privileges/comment); instead, [provide answers that don't require clarification from the asker](https://meta.stackexchange.com/questions/214173/why-do-i-need-50-reputation-to-comment-what-can-i-do-instead). - [From Review](/review/late-answers/34371992) – user16217248 May 15 '23 at 23:19

"vector" was not declared in this scope

2 Answers2