Error `no nombra un tipo` con `namespace std;` y archivos

compiling the code below with g++ main.cpp functions.cpp -o run me da el error error: ‘vector’ does not name a type. Declaring namespace at the top of main.cpp usually works across all .cpp archivos para mí.

main.cpp 

using namespace std;

#include "functions.h"

main () {}

funciones.h

#include <vector>

funciones.cpp

#include "functions.h"
vector <int> x;

EDIT: I appreciate the fact all responders know what their talking about, but this normally works for me. Would the use of a makefile have any bearing on that? something else that I might be missing?

preguntado el 28 de agosto de 12 a las 12:08

4 Respuestas

Yes but in this example functions.cpp no ha visto using namespace std since you only wrote that in main.cpp.

No agregue using namespace std a functions.h, Utilizar std:: to qualify types. Adding a using.. imposes an unnecessary burden on the user of your header.

Respondido 28 ago 12, 12:08

You need to qualify the namespace:

#include "functions.h"
std::vector<int> x;

Tiene using namespace std in main.cpp, and it cannot be seen by functions.cpp. That is the root of the problem.

En general, debes evitar using namespace std, specially in headers. And if you really must include it in main, put it after all the headers.

Respondido 28 ago 12, 12:08

I will change downvote to an upvote for anyone who adresses the fact that this usually works for me. Even your answers is only speculative. - matt munson

@MattMunson it cannot possibly work for you (in this particular case), because using namespace std is not seen in functions.cpp. And assuming that using namespace std can be seen somewhere can only lead to trouble. - juanchopanza

Importaste el std namespace only in main.cpp, no en functions.cpp.

You have to qualify your use - std::vector in the second file, or use the using directiva:

//functions.cpp
#include "functions.h"
std::vector <int> x;   // preferred

or

//functions.cpp
#include "functions.h"
using namespace std;
vector <int> x;

or (bonus)

//functions.cpp
#include "functions.h"
using std::vector;
vector <int> x;

Declaring namespace at the top of main.cpp usually works across all .cpp files for me.

You have a really flawed compiler then. using directives shouldn't influence translation units that don't have direct visibility over the directive.

Respondido 28 ago 12, 12:08

Usted using namespace std is local to main.cpp only. You need to use

 std::vector<int> x;

in your source file functions.cpp

Respondido 28 ago 12, 12:08

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