I have no idea what's going on

I'm extremely new to C++... This is my code:

Code:

---

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    char string(50);
    cout << "Enter file name:";
    cin.getline (string, 50, '/0');

}

---

I am getting the following error/warning messages:

C:\Users\Bayne\HEytl\main.cpp|10|error: invalid conversion from 'char' to 'char*'|

C:\Users\Bayne\HEytl\main.cpp|10|error: initializing argument 1 of 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::getline(_CharT*, std::streamsize, _CharT) [with _CharT = char, _Traits = std::char_traits<char>]'|

C:\Users\Bayne\HEytl\main.cpp|10|warning: overflow in implicit constant conversion|

What's wrong here?

The implicit conversions are happening because you have a typo. You do not declare an array with the size in parentheses.

Code:

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char string[ 50 ];

---

First you should not use the name "string" for a variable name in C++. This is the name of a standard C++ class.

Second: To define a C-string variable you need to use brackets "[]" not parentheses "()".

Jim

Quote:

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Originally Posted by theworldluvsu

Code:

---

int main()
{
    char string(50);
    cout << "Enter file name:";
    cin.getline (string, 50, '/0');
...

---

---

If you are programming in C++ there is no need to use C style strings. Look at using the std::string class. A good introduction to this can be found here.

If you are serious about learning C++, learn how to code C++ style and avoid list C or "almost C" programs (as Bjarne would say).

Part of the problem is that there is a class named string in the namespace std, which you so casually import into the global namespace. And obviously you cannot reserve a name for a variable that is already reserved for a type (ie, a class).
Use std::string instead of char and std::getline instead of std::cin.getline.

Quote:

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Originally Posted by Elysia

Part of the problem is that there is a class named string in the namespace std, which you so casually import into the global namespace. And obviously you cannot reserve a name for a variable that is already reserved for a type (ie, a class).
Use std::string instead of char and std::getline instead of std::cin.getline.

---

Quote:

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Originally Posted by jimblumberg

First you should not use the name "string" for a variable name in C++. This is the name of a standard C++ class.

---

"string" is not, never has been, and won't be a reserved word. A hint comes from syntax highlighting: reserved words are highlighted blue or some other color. What can happen is name clashing; but that only happens if OP actually types #include <string> AND using namespace std; one of which he did not do here. "string" is a perfectly acceptable identifier, especially after you pick up the habit of avoiding using namespace whatever;

That depends. It's also a perfectly meaningless identifier for a variable. If it's called string, that doesn't give you any information you didn't already have. In the OP's example, fileName would have been a good name.

Quote:

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Originally Posted by whiteflags

"string" is not, never has been, and won't be a reserved word. A hint comes from syntax highlighting: reserved words are highlighted blue or some other color. What can happen is name clashing; but that only happens if OP actually types #include <string> AND using namespace std; one of which he did not do here. "string" is a perfectly acceptable identifier, especially after you pick up the habit of avoiding using namespace whatever;

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When you realize that a header can implicitly include others, you realize that it isn't safe to use "using namespace std;" and any reserved names for a class. On this compiler, the OP got away with it, but who can say what happens with other compilers?
Also some things others haven't commented on:

char string(50);

is valid syntax, and created a single char named "string" and initializes it with the values 50. So it is valid syntax, but it isn't logically correct.
Also, '/0' should be '\0'.

Quote:

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Originally Posted by Elysia

When you realize that a header can implicitly include others, you realize that it isn't safe to use "using namespace std;" and any reserved names for a class. On this compiler, the OP got away with it, but who can say what happens with other compilers?

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You're completely wrong on this. There are lists of reserved words available and string isn't on that list. If you don't trust this source, you can find others. I defy you to find "string" on any list. The whole point of using namespaces (ETA: not to be confused with "using namespace std;" but I'm implying saner usage) is preventing name clashing. If string were a reserved word, it wouldn't need to be in a namespace.

I didn't say it was a reserved keyword. It's a reserved name for a class living inside the std namespace.
It so happens the OP imports the entire std namespace and dumps it into the global namespace, which makes the word "string" a dangerous thing to use as a variable name.

Valid identifiers are never reserved for any purpose.

Let's get really crazy:

Code:

---

#include <string>
#include <iostream>
void foo()
{
  std::string string;
  string = "hello\n";
  std::cout << string;
}

---

It might be meaningless but this does compile. So "reserved" is really the wrong thing to say.

If you say so.
My point is, that if you add "using namespace std" in there and use string, you might just run into compile errors on some compilers.
If you include "string", you will get an error on all standard compliant compilers.
If you're unlucky and and haven't included "string", you might still get compile errors.

Indeed, the problem is "using namespace std;" and nothing else.

Absolutely.

Quote:

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Originally Posted by Elysia

If you say so.
My point is, that if you add "using namespace std" in there and use string, you might just run into compile errors on some compilers.
If you include "string", you will get an error on all standard compliant compilers.
If you're unlucky and and haven't included "string", you might still get compile errors.

---

No you won't.

I agree that using identifiers from the standard library is best avoided, but C++ name lookup tends to do the right thing. It is allowed to have two identifiers with the same name where one broad scope includes the narrower scope of the other identifier. In this case, where there is overlap, the narrower scope is preferred.

what everyone seems to be failing to realize is that even when a "using namespace std" declaration is employed in the global scope, a member of a child scope may still be called by any of the names defined in the global scope. child scope names have precedence over parent scope names. take the following code for example:

Code:

---

#include <iostream>
#include <string>

using namespace std;

int main(void)
{
        char* string = nullptr;
        return 0;
}

---

the variable called "string" in main() does not conflict with std::string, because the C++ compiler takes any unqualified identifier to mean the one defined in the nearest scope.

even the following code is valid:

Code:

---

#include <iostream>
#include <string>

using namespace std;

int main(void)
{
        typedef char* string;
        string s = nullptr;
        return 0;
}

---

I have confirmed this behavior on both G++ 4.5.1 and VC++ 2010.

That's true even if using namespace std is in the child scope.

And who's "everybody"? your example is virtually identical to the one I linked to.

For more confusion, try this:

Code:

---

#include <string>
#include <iostream>
int main()
{
  using namespace std;
  string string;
  string = "hello\n";
  cout << string;
}

---