Use of string

[Luis]

Hi all,
I am learning C++ using a book by Bruce Eckel, Thinking in C++. I have hit a problem when solving an exercise at the end of one of the chapters which left me a bit confused.
I need to create a struct which has three string objects as its members. This is my code for the header file:

#include <string>

struct TestStruct
{
string a, b, c;
};


I also have the implementation .cpp file for it.
I included the header file on the file where I am using it but the compiler comes up with the error "string does not define a type".
I can see what he sort of means, as string is not a native type, but I can not find a way of solving it.
Is there a problem with my struct declaration?

Thanks.
Best Regards
Luis

[Smok006]

I don't know for sure, but u might try including STRING.H.

[z05DSL3A]

#include <string>

struct TestStruct
{
     std::string a, b, c;
};

[Luis]

Hi Grey Wolf,
I have tried that and it did not work. This is the error given now: "using-declaration for non-member at class scope"
best Regards
Luis

[hannad]

Not sure but also try this :P

using namespace std;

[z05DSL3A]

Luis, What compiler/IDE/platform are you using?

You also say you "have the implementation .cpp file for it", there is no need for any implementation other than the code you posted.

Can you post your code? using code tags ie:
[code]
your header code...
[/code]
[code]
your imp code...
[/code]

[Luis]

Hi Grey Wolf,
this is my code:

[TestStruct.h]
//TestStruct.h
#include <string>

struct TestStruct
{
string a, b, c;
};
[/TestStruct.h]

[TestStruct.cpp]
//TestStruct.cpp
#include "TestStruct.h"

TestStruct.a = "";
TestStruct.b = "";
TestStruct.c = "";
[/TestStruct.cpp]

[CH5Exe2.cpp]
//Ch5Exe2.cpp
// usage
#include <cstdlib>
#include<iostream>
#include "TestStruct.h"

using namespace std;

int main(int argc, char *argv[])
{
TestStruct x;
x.a = "2";
x.b = "3";
x.c = "4";

cout<< x.a << endl;
cout<< x.a << endl;
cout<< x.a << endl;

system("pause");
return EXIT_SUCCESS;
}

[/CH5Exe2.cpp]

Thanks
Luis

[z05DSL3A]

The problem is TestStruct.cpp, you do not need it. If you comment out the three line it should work.

//TestStruct.h
include <string>

struct TestStruct
{
     std::string a, b, c;
};

//TestStruct.cpp
#include "TestStruct.h"

//TestStruct.a = "";
//TestStruct.b = "";
//TestStruct.c = ""; 

PS, what I meant by use code tags, was put the actual text [code] above, you code and [/code] below it.

if you type in

[code]
//TestStruct.cpp
#include "TestStruct.h"

//TestStruct.a = "";
//TestStruct.b = "";
//TestStruct.c = "";
[/code]

it is displayed as

//TestStruct.cpp
#include "TestStruct.h"

//TestStruct.a = "";
//TestStruct.b = "";
//TestStruct.c = ""; 

edit:corrected spelling mistakes

[Luis]

Hi,
The IDE I am using is DEVC++/MinGW on Windows.
Regards
Luis

[Luis]

Hi,
The original error as gone but I have a new one:
"using-declaration for non-member at class scope"
Best Regards
Luis

[z05DSL3A]

I do not use DevC++ but would expect there to be more information than just "using-declaration for non-member at class scope".

somthing like:
TestStruct.cpp:4: using-declaration for non-member at class scope
can you post it please.

[Luis]

there is nothing else there except for:
"using-declaration for non-member at class scope
expect ';' before "a" "

[z05DSL3A]

Okay, as I can't tell where that is having a problem try this:

1) remove the TestStruct.cpp file altogether from your project.
2) make sure the two files you have left look like this:

//TestStruct.h
#include<string>

struct TestStruct
{
     std::string a, b, c;
};

//Ch5Exe2.cpp
// usage
#include<iostream>
#include "TestStruct.h"

using namespace std;

int main(int argc, char *argv[])
{
    TestStruct x;
    x.a = "2";
    x.b = "3";
    x.c = "4";

    cout<< x.a << endl;
    cout<< x.a << endl; 
    cout<< x.a << endl;

    system("pause");
    return EXIT_SUCCESS;
}

3) Find the clean or rebuild build option and perform a fresh build.

NB: You have cout<< x.a << endl; three times in your main, you may have wanted to have one for x.a, x.b, and x.c but that is insadental.

[Luis]

Hi,
I see what you mean, and it probably will work, but I would like to know why using the .cpp file does not work.

The other thing is that on this book the author says that using the "using"directive(I presume that "std::string a, b, c;" is a sort of using directive) in a .h file was not desirable.

thanks for your help
Luis

[z05DSL3A]

As I said before; there is nothing in your header file that needs implementing, the empty .cpp file could possibly have confused the compiler.

The following file uses the "using" directive

//TestStruct.h
#include<string>
using namespace std;

struct TestStruct
{
     string a, b, c;
};

It is not desirable to do this because it would bring all items in the std namespace into what ever scope the header is included in.

Full scope resolution (ie namespace::item) is what you should do in headers.

[Luis]

Hi Grey Wolf,
thank you for your help, it did work.
As I am just starting, I am trying to get a programming standard, but obviously it does not work for everything.
Best Regards
Luis

[mordekai]

I guess the error is too obvious to see it, eh?

//TestStruct.cpp
#include "TestStruct.h"

TestStruct.a = "";
TestStruct.b = "";
TestStruct.c = "";

TestStruct is a structure and you never declared a variable. You have to do it this way:

//TestStruct.cpp
#include "TestStruct.h"

TestStruc mystruc;

mystruc.a = "";
mystruc.b = "";
mystruc.c = "";

[z05DSL3A]

I guess the error is too obvious to see it, eh?

No, not if you think that was the error.