Problems with multiple files

Hi

I am working with multiple files in my program, and I have really confused myself. I have tried condensing my problem for this question. First an overview of the 4 files in the program:

My main.cpp is

Code:

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#include <iostream>
#include <vector>
#include "constants.h"
#include "ext1.h"

using namespace std;

int main() {
        vector<double> temp;
        vector<double>::iterator i;

        ext_func();

        return 0;
}

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There is one external file "ext1.cpp". The variable b must only be visible to functions within "ext1.cpp", but all other variables declared in "main.cpp" it should have access to.

Code:

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#include <iostream>
#include <vector>
#include "constants.h"

int b = 2; // this must only be visible to ext1.cpp

int ext_func() {

        i = temp.begin();
        cout << *i << endl;
}

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The header for "ext1.cpp", "ext1.h"

Code:

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#ifndef EXT1_H
#define EXT1_H

int ext_func();

#endif

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The final header "constants.h", which is visible to both .cpp-files

Code:

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#ifndef CONSTANTS_H
#define CONSTANTS_H

const int a = 2;

#endif

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My program does not compile. There is an error "1 unresolved externals". Can I get a hint to the error? Besides that I am not sure that the scope for the different variables is as I have intended, but once I can compile, I will be able to test it out.

Thanks for the help in advance.

Best,
Niles.

So if you do "build all", do you see both "ext1.cpp" and "main.cpp" being compiled.

Posting the actual name of the thing which is unresolved would help.

Hi, thanks for replying.

Quote:

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Originally Posted by Salem

So if you do "build all", do you see both "ext1.cpp" and "main.cpp" being compiled.

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Oh, I hadn't compiled "ext1.cpp". But now there are 6 errors, all related to "ext1.cpp". "i", "cout", "endl" and "temp" are undeclared identifiers and the final two errors are related to "<<" and ">>". So somehow iostream is not included in "ext1.cpp", but I have included it explicitly.

But ext1.cpp doesn't have
using namespace std;

Ah, you are right. "ext1.cpp" still can't see "i" and "temp", I was under the impression that everything declared in "main.cpp" was visible to all other "sub"-files(?)

Quote:

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Originally Posted by Niels_M

"sub"-files(?)

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There is nothing as 'sub' files.
Perhaps, that is where your confusion comes from.
The only tool you have is the #include directive (and #define header guards, to prevent problems with that 'inclusion' model) , so,

if X is declared in x.h and you want to 'see' it in y.cpp, you have to #include "x.h" to get it.
But, don't #include files which contain function definitions, as the declaration is sufficient for using them.
Everything else is ideally done by the linker.

Quote:

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Originally Posted by manasij7479

There is nothing as 'sub' files.
Perhaps, that is where your confusion comes from.
The only tool you have is the #include directive (and #define header guards, to prevent problems with that 'inclusion' model) , so,

if X is declared in x.h and you want to 'see' it in y.cpp, you have to #include "x.h" to get it.
But, don't #include files which contain function definitions, as the declaration is sufficient for using them.
Everything else is ideally done by the linker.

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Thanks to both of you, that helped me!