xy was not declared in this scope: compiler error!

Hey everybody,

I finished lesson 10 today, fileio, and thought "Hey, let's combine all I have learned before.

So I programmed a simple menu with switchcase, and thought I would give the user the choice between writing something into a file, read a file and print the content out, append something to a file or exit.
But when I wanted to test my first function (i.e. write something to a file) I get the following errors and can't quite figure it out :-( I bet it is quite simple!!

Any help is highly apreciated :-)

Code:

---

~ thommy$ g++ switchfileio.cpp -o littletest
switchfileio.h: In function ‘void write_file()’:
switchfileio.h:15: error: ‘cout’ was not declared in this scope
switchfileio.h:16: error: ‘cin’ was not declared in this scope
switchfileio.h:21: error: ‘ofstream’ was not declared in this scope
switchfileio.h:21: error: expected `;' before ‘a_file’
switchfileio.h:22: error: ‘a_file’ was not declared in this scope
switchfileio.h: In function ‘void read_file()’:
switchfileio.h:28: error: ‘cout’ was not declared in this scope
switchfileio.h: In function ‘void appendto_file()’:
switchfileio.h:32: error: ‘cout’ was not declared in this scope
:~ thommy$

---

This is what I got so far:

File: switchfileio.cpp

Code:

---

#include <iostream>
#include <fstream>
#include "switchfileio.h"

using namespace std;

int main(){
        int input;                // need this one for the switch-case-menu

        do {                        // this is the menu, it works, have tried this with another lesson!
                cout<<"1. Write something to a file\n";
                cout<<"2. Read a file and print its content\n";
                cout<<"3. Append a string to an existing file\n";
                cout<<"4.Exit\n";
                cin>>input;               
                switch (input) {
                        case 1:
                                write_file();
                                break;
                        case 2:
                                read_file();
                                break;
                        case 3:
                                appendto_file();
                                break;
                        case 4:
                                cout << "Thanks for playing with me\n";
                                break;
                        default:
                                cout<<"Error\n";
                                break;
                }
        } while (input == 1 || input == 2 || input == 3 || input == 4);  // this is to redraw the menu when one operation is done
               
       
        cin.get();
}

---

File: switchfileio.h

Code:

---

void write_file(){                        // my function that is called when the user wants to write a file
        char string[256];                // this is the string the user can enter
        char filename[15];                // this string is used to determine the filename of the file
        cout << "Please enter your text!\n";
        cin >> string;
        cout << "You entered: " << string <<"\n";        // show the user what he has written
        cout << "Please enter a filename: ";                // ask for the filename
        cin >> filename;
       
        ofstream a_file (filename);                // creates an instance of ofstream and opens a file with the content of filename
        a_file<<string;                                        // write the content of "string" into the file
        a_file.close();                                        // close the file
        cout << "file " << filename <<" is written!\n";  // give success message to the user
}

void read_file(){
        cout << "you just loaded\n";
}

void appendto_file(){
        cout << "sorry, MP is not ready yet\n";
}

---

The include simply pastes the contents of the file and replaces the include row. So that contents if placed above the using namespace directive, causing all your errors.
But, aside from that, here are a couple of suggestions for you:
1) It's not usually a good idea to inline functions in headers. They are usually the place for declarations.
2) It's not a good idea to use using directives in headers either. So use the std:: prefix in them.
3) Use std::string and std::getline instead of char.

Code:

---

#include "switchfileio.h"

using namespace std;

---

The using namespace is after the included header, either place before the header include or move into the header.

Do you know what does 'scope' mean? And what about function prototypes? Use std::cout instead and add prototypes to your cpp. Like this:

Code:

---

void read_file();

---

Prototypes goes into headers. Put the header code in the .cpp file instead.
There might not even be a need for a header in this code since it's a single source file.

ok everybody, thanks a lot for your quick answers.

Putting the code from the .h file under the "using" did the trick. Thanks!!

As I said: I am going by the tutorial and I am at lesson 10. And so I am quite bound to what I know from that 10 lessosns so far:

Elysia:

1.: Functions in headers: Lesson learned, functions don't go into the header! The reason why I did that was that I thought I'd only put the main() into the main-source file, and hav everything else in other files.
2.: Using directives in the header: That is the way the tutorial does it, right now I have no clue what they mean. That was not covered in the tutorial yet. It just said "do it that way", so I did. I had no idea for example that I could use std::cout instead of "using namespace std;" and then just cout.
3.: std::string and std::getline was not covered yet, either. The tutorial said it will come a little later. The lesson about strings just said "we are using the C-style strings for now, i.e. char string[50];

GL.Sam:

quite frankly, I have no idea about "scope" in that context. I understand the word, but have no idea about what it means in c++ or programming itself, for that matter.

The tutorial said something about prototypes, but did not say where they would go nor where I would write the actual function. It even said: We are not using prototypes for now.

Elysia: Prototypes goes into headers? So I would say:

Code:

---

#include <whatever>

void write_file();

main()...

---

and where would I really define the function then?

Thanks again for all answers :-) I really like communities, and hopefully this one will become one where I can give something back somewhen. In others I do, in this area (programming) I feel like a total loser :-D

In another cpp file.

Every cpp needs to be compiled into an object file, and then they all need to be linked to produce the final binary. Fortunately, GCC does all that for you.

Say you have the 3 functions in util.cpp.

Code:

---

g++ switchfileio.cpp util.cpp -o littletest

---

You may also want to use inclusion guards (google it).

thanks.

so my guess was right: I prototype the function in the header, and then I use it in my main as I whish, but having it actually defined in another .cpp-file

I just googled include guards, seems to be a good thing. It will be covered in the tutorial as last lessons, hence the tutorial does not make use of self-written header files yet. I just did because I thought it would be fun to try things besides the tutorial :-)

I guess I will continue to work on my little test-program with those tipps in mind and try to get it wo actually work! but not today :-(

thx!

Quote:

---

#include <whatever>

void write_file();

main()...

---

Thats not the header file, the head file would be whatever.h. Also, < > brackets tells the compiler to look in the global space, if you are just adding you own header, you should use #include "whatever.h" as this tells the compiler to look in the current directory of your program.

Also, a header would be like this -

Code:

---

//whatever .h
#ifndef _WHATEVER_H
#define _WHATEVER_H

void do_something();

#endif

---

And then the cpp as follows

Code:

---

//whatever.cpp
#include "whatever.h"

void do_something()
{
//do something
}

---

and finally in main.

Code:

---

#include "whatever.h"

int main()
{
  do_something();
  return 0;
}

---

thx Spidey,

that really helped me to understand what goes where. What you first said I already knew, but maybe I said it wrong, but the rest was something I definitly needed :-)

And as Elysia told me, I would use std::getline and std::string instead of my char-thing.

When I tried to compile my my program with the new code in function "write_file()" in util.cpp, I get some other errors. I am mainly confused about the "20: error: cin was not declared in this scope". That is line 20, which is my call std::getline (std::cin,filename); which I took from the cplusplus-reference.

Code:

---

thommy$ g++ switchfileio.cpp util.cpp -o test
util.cpp: In function ‘void write_file()’:
util.cpp:20: error: ‘cin’ was not declared in this scope
util.cpp:27: error: no matching function for call to ‘std::basic_ofstream<char,
std::char_traits<char> >::basic_ofstream(std::string&)’
/usr/include/c++/4.0.0/fstream:574: note: candidates are: std::basic_ofstream
<_CharT, _Traits>::basic_ofstream(const char*,
std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.0.0/fstream:558: note:  std::basic_ofstream<_CharT, _Traits>::basic_ofstream()
[with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.0.0/iosfwd:92: note:  std::basic_ofstream<char, std::char_traits<char> >
::basic_ofstream(const std::basic_ofstream<char, std::char_traits<char> >&)
thommy$

---

So I now have 3 files:

util.h:

Code:

---

#ifndef _UTIL_H
#define _UTIL_H

// prototyping the functions here, they are declared in util.cpp

void write_file();
void read_file();
void appendto_file();

#endif

---

util.cpp:

Code:

---

#include <iostream>
#include <fstream>
#include "util.h"

void write_file(){                        // my function that is called when the user wants to write a file
               
        std::string text;
        std::string filename;
       
        std::cout<<"Please enter your text, end with pressing 'Enter'\n";
        std::getline (std::cin,text);
        std::cout <<"You entered: " << text << " \n";
       
        std::cout<<"Please enter a filename to name the file your text is saved to: \n";
        std::getline (std::cin,filename);
        std::cout <<"You entered: " << filename << " \n";
       
        std::ofstream file (filename);
        file<<text;
        file.close();
       
        std::cout <<"your file " << filename << "was written successfully.\n";
}

void read_file(){
        std::cout << "sorry, feature has yet to be coded...\n";
}

void appendto_file(){
        std::cout << "coding in progress... please hold the line...\n";
}

---

and finally, switchfileio.cpp:

Code:

---

#include <iostream>
#include <fstream>
#include "util.h"

int main(){
        int input;                // need this one for the switch-case-menu

        do {                        // this is the menu, it works, have tried this with another lesson!

                std::cout<<"1. Write something to a file\n";
                std::cout<<"2. Read a file and print its content\n";
                std::cout<<"3. Append a string to an existing file\n";
                std::cout<<"4.Exit\n";
                std::cin>>input;               
                switch (input) {
                        case 1:
                                write_file();
                                break;
                        case 2:
                                read_file();
                                break;
                        case 3:
                                appendto_file();
                                break;
                        case 4:
                                std::cout << "Thanks for playing with me\n";
                                break;
                        default:
                                std::cout<<"Error\n";
                                break;
                }
        } while (input == 1 || input == 2 || input == 3);  // this is to redraw the menu when one operation is done               
       
        std::cin.get();
}

---

The ofstream constructor takes a C style string, not a std::string.

Code:

---

std::ofstream file (filename.c_str());

---

Quote:

---

Originally Posted by twilight

thx Spidey,

that really helped me to understand what goes where. What you first said I already knew, but maybe I said it wrong, but the rest was something I definitly needed :-)

And as Elysia told me, I would use std::getline and std::string instead of my char-thing.

When I tried to compile my my program with the new code in function "write_file()" in util.cpp, I get some other errors. I am mainly confused about the "20: error: cin was not declared in this scope". That is line 20, which is my call std::getline (std::cin,filename); which I took from the cplusplus-reference.

---

Are you this is the code you compiled?
Except for the missing <string> header and using a C-style string to open the file (as bithub points out), the code compiles fine.

yes, I am sure that is the code that got compiled. :-)

So my strings are in fact objects, right? And the c_str(); method from my file gives back a classic c-string?!

Changed the code acordingly, and now it compiles without error, although it did not do
what I wanted it to correctly.

Now I fixed two "bugs" in the code, and guess what: My program actually writes all the text I entered into the file and saves the file acording to the name I entered. Woohoo :-)

I also had to add an cin.ignore(); in my main file so that the enter from chosing the options in the menu would not skip the text-enter-part. First I wanted to have it in the write_file() method, but then I thought I would need it in my read_file(); method as well, so I think it is better of after the input of the menu-option!

thx guys :-)

Code:

---

void write_file(){        // my function that is called when the user wants to write a file
               
        std::string text;
        std::string filename;

        std::cout<<"Please enter your text, end with pressing 'Enter'\n";
        std::getline (std::cin,text);
        std::cout <<"You entered: " << text << " \n";
       
        std::cout<<"Please enter a filename to name the file your text is saved to: \n";
        std::getline (std::cin,filename);
        std::cout <<"You entered: " << filename << " \n";
       
        std::ofstream file (filename.c_str());
        file<<text.c_str();
        file.close();
       
        std::cout <<"your file " << filename << " was written successfully.\n";
}

---

Quote:

---

Originally Posted by twilight

So my strings are in fact objects, right? And the c_str(); method from my file gives back a classic c-string?!

---

Yes.

>> So my strings are in fact objects, right?
Correct.

>> And the c_str(); method from my file gives back a classic c-string?!
Yes.

:-) thx again!

so, I just had some time and thought "hey, let's begin with the second method (i.e. read_file();)

I made some mistakes, now it works that it does recognize when there is no file that could be opend AND it opens a file, and prints out the first word. Why only the first word? Shouldn't it print out the whole content of the file?

Code:

---

void read_file(){

        std::string readfile;        // this is the object where the filename goes into
        std::string readtext;        // this is the object where the read in text goes into
        std::cout << "Please enter the filename of the file you want to open: \n";
        std::getline(std::cin,readfile);        // get the user to input the filename
        std::ifstream userfile (readfile.c_str());

        if(!userfile.is_open()){    // check if the file could be opend
                std::cout<<"The file you tried to open could not be opened, sorry!";
        }else{
                std::cout<<"You loaded the file " << readfile << "! Content below\n";
                userfile>>readtext;
                std::cout<<readtext;
        }
}

---

The >> operator only reads a word by default. Use std::getline.

thanks, that did the trick :-)

the tutorial used the >> operator with a char text[] and it worked with more than one word, so I thought I could use it the same way with the ifstream-struct, but that was wrong as it seams.

Now it works!

changed the line from userfile>>readtext; to getline(userfile,readtext);

Edit says: wait a minute. I just switched to eclipse for writing my files, and it gave me an error once (not now) saying ifstream was a struct. In the c++.reference i just read it says ifstream is a class?! Why would eclipse call it a struct?

So, after I got a little confused with how the tutorial on this page explains things, I found myself another tutorial, that suits me "needs" way better i.e. describes things how I need to hear them to understand. So now I am following 2 tutorials and using them complementary.

Anyhow, I tried to get on with my little program, so I had at least one thing finished ;-) Here is my new void appendto_file() - function. When I compile it, I get the following errors, what do I wrong? Thanks again for any help!! :-)

Code:

---

../util.cpp: In function 'void appendto_file()':
../util.cpp:76: error: no match for 'operator==' in 'isfile == 'y''
../util.cpp:76: error: no match for 'operator==' in 'isfile == 'Y''
../util.cpp:81: error: 'ios' has not been declared
../util.cpp:81: error: 'app' was not declared in this scope

---

Code:

---

void appendto_file()
{
        std::cout << "Please enter the filename of the file you want to append text to: ";
        std::string filename;
        std::getline(std::cin,filename);
        std::cout << "\n";

        std::ifstream appendfile (filename.c_str());
        if(!appendfile.is_open())
        {
                std::cout<<"The file you tried to open could not be opened, sorry!\n";
        }
        else
        {
                std::cout<<"Is this the file, you wanted to open?\n\n";
                std::string readtext;
                getline(appendfile,readtext);
                std::cout<<readtext;
                std::cout<<"\n\n";
                std::cout<<"Enter y for yes and n for no: ";
                appendfile.close();
                std::string isfile;                  // now we want to check if that was the file or not.
                std::getline(std::cin,isfile);
                if(isfile == 'y' || isfile == 'Y')
                {
                        std::cout<<"Please enter the text you want to append: \n";
                        std::string appendtext;
                        std::getline(std::cin,appendtext);
                        std::fstream appendfile (filename, ios::app);
                        appendfile<<appendtext;
                        appendfile.close();
                }
                else
                {
                        std::cout<<"Sorry, please try again!\n";
                }
        }
}

---

You cannot check whether a string equals a character, because it can't. Perhaps you want to check whether the string equals the string "Y".

Also, it's std::ios::app.

thx, I changed ios::app into std::ios::app.

Ok, so check a string against a character is not possible. Makes sense I guess. :-D But what when I use the string.c_str()-function. So to say:

Code:

---

if(isfile.c_str() == 'y' || isfile.c_str() == 'Y')

---

When I do that, the compiler complains about:

Code:

---

../util.cpp:76: error: ISO C++ forbids comparison between pointer and integer

---

But I seem to fail to see where I use a pointer.

Code:

---

if(isfile.c_str()[0] == 'y' || isfile.c_str()[0] == 'Y')

---

Of course in this case, you can just drop the c_str()

Code:

---

if(isfile[0] == 'y' || isfile[0]== 'Y')

---

thx, the error is now gone.

just for my understanding: isfile[0] looks like I am accessing the first char of an array of chars, but isfile is a string, or more precisely: an object. What exactly does the [0] do with an object?

Also, the following line now gets an error it did not get before :-(

Code:

---

std::fstream appendfile (filename, std::ios::app);

---

error:

Code:

---

../util.cpp: In function 'void appendto_file()':

../util.cpp:86: error: no matching function for call to 'std::basic_fstream<char, std::char_traits<char>
>::basic_fstream(std::string&, const std::_Ios_Openmode&)'

/usr/include/c++/4.0.0/fstream:704: note: candidates are: std::basic_fstream<_CharT, _Traits>
::basic_fstream(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits<char>]

/usr/include/c++/4.0.0/fstream:690: note: std::basic_fstream<_CharT, _Traits>::basic_fstream()
[with _CharT = char, _Traits = std::char_traits<char>]

/usr/include/c++/4.0.0/iosfwd:95: note: std::basic_fstream<char, std::char_traits<char> >
::basic_fstream(const std::basic_fstream<char, std::char_traits<char> >&)
make: *** [util.o] Error 1

---

The [] operator can be overloaded by any object. std::string overloads it to return the character at the passed index.

The fstream constructor takes a C style string, not a std::string. Add a .c_str() to the end of filename.

oh, man. I had that once before :-( thx for the hint again!!

now it works. At least, it compiles. my appendto_file() function now asks for the filename, prints an error if it can't be opened, prints the content of the file if it can be opened.

the question if this is the right file works, too. y and Y gives the expected result, n or anything else too.

But what happens when the user presses y and then inputs his text is another question. The user can input text, but that text does not get appended :-( So something in the following code-snippet must be wrong:

Code:

---

std::cout<<"Please enter the text you want to append: \n";
std::string appendtext;
std::getline(std::cin,appendtext);
std::fstream appendfiletwo;
appendfiletwo.open (filename.c_str(), std::ios::app);
appendfiletwo<<appendtext.c_str();
appendfiletwo.close();

---

Quote:

---

Originally Posted by twilight

When I do that, the compiler complains about:

Code:

---

../util.cpp:76: error: ISO C++ forbids comparison between pointer and integer

---

But I seem to fail to see where I use a pointer.

---

c_str() returns a legacy C-style string and in C, a string is considered to be a pointer to char (char*). c_str() returns const char*, thus you try to compare a const char* to char, which is illegal (and it's not sensible either).

oh, tanks, that clears that issue :-)

what about my code-snippet from the most recent post? Any hint you have for me there?

I just thought a further check would be nice to see if the file-opening for the fstream worked out, so I changed the snippet from:

Code:

---

std::cout<<"Please enter the text you want to append: \n";
std::string appendtext;
std::getline(std::cin,appendtext);
std::fstream appendfiletwo;
appendfiletwo.open (filename.c_str(), std::ios::app);
appendfiletwo<<appendtext.c_str();
appendfiletwo.close();

---

into:

Code:

---

std::cout<<"Please enter the text you want to append: \n";
std::string appendtext;
std::getline(std::cin,appendtext);
std::fstream appendfiletwo;
appendfiletwo.open (filename.c_str(), std::ios::app);

if(!appendfiletwo.is_open())
{
        std::cout<<"Your file could not be opend for appending, sorry.\n";
}
else
{
        appendfiletwo<<appendtext.c_str();
        appendfiletwo.close();
        std::cout<<"Your data has been appended!\n";
}

---

And guess what I am getting when I try to append something?

Your file could not be opend for appending. So something is not working with my fstream. But what? I can't figure it out right now :-(

Edit: a string does not lose it's content once I used it by string.c_str() or does it? If it does it would be clear why fstream could not open, because my string is empty. But if it does not, then I have a problem I really can't see :-(

Is the name what you think it is?

(Since this is called filetwo....) Is the file already open?

I just realized I never closed the file in my read_file() function. I now added the close-method, but the error remains.

In my whole appendto_file()-Method I am doing 2 things:
- I am opening and showing the content of a usergiven file, and close that ifstream-object named 'appendfile'.
- I am re-opening the file, using fstream, creating an object named 'appendfiletwo', appending a usergiven
content to that usergiven file, and close the fstream.

I just used two different names for the ifstream-object and for the fstream-object, in order do distinguish between them.

fopen should set errno on error, so you can use strerror to get an appropriate message, I suppose. Were it me, I would double check things are closed, and that the file name is what I expect.

well, I am using the same filename the user typed in before and I saved in a string, named filename.

So, the filename should be the same.

Just for the sake of argument here: Am I doing something wrong? I am the kind of guy that wants to see if something works and afterwards I am thinking about security or double-checking, when the user has to deal with it or anything.

Quote:

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Originally Posted by twilight

well, I am using the same filename the user typed in before and I saved in a string, named filename.

So, the filename should be the same.

Just for the sake of argument here: Am I doing something wrong? I am the kind of guy that wants to see if something works and afterwards I am thinking about security or double-checking, when the user has to deal with it or anything.

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Since it's not working, the answer to that is probably "yes". The exact nature of what you're doing wrong is what we're trying to determine here.

Easy question: if it's the same file, why are you opening and closing and opening and closing and opening and closing and etc.? Why not just open the file and pass the stream around?

hmm... ok. I have thought of that, too. But could not figure out how.

istream is just for inputing files from harddrive to my program, right? ofstream is just for outputting files from program to harddrive. Whereas fstream should be doing both as well as append, as far as I know?!

Also, could I open a file and pass it from one function to another? I guess not because my object only has function-scope, when I open it in one function, right?

So the only thing I could do is to open it once instead of twice in my appendto_file()-function.

I can't use ofstream for that, I can't use ifstream for that. So I would fstream? What about fopen you mentioned? I am somewhat limitted to what I know from the 2 tutorials so far, fopen was not covered yet. How is the usage, any reference?

Quote:

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Originally Posted by twilight

hmm... ok. I have thought of that, too. But could not figure out how.

istream is just for inputing files from harddrive to my program, right? ofstream is just for outputting files from program to harddrive. Whereas fstream should be doing both as well as append, as far as I know?!

Also, could I open a file and pass it from one function to another? I guess not because my object only has function-scope, when I open it in one function, right?

So the only thing I could do is to open it once instead of twice in my appendto_file()-function.

I can't use ofstream for that, I can't use ifstream for that. So I would fstream? What about fopen you mentioned? I am somewhat limitted to what I know from the 2 tutorials so far, fopen was not covered yet. How is the usage, any reference?

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fopen is C.

Of course you can pass things from function to function. You wouldn't flinch at:

Code:

---

int my_function(int bob) {
    int joe = bob + 6;
    joe = process(joe);
    return joe;
}

---

would you? Yet you're passing a local variable, namely joe, off to another function.

ifstreams can only be used for input, and ofstreams can only be used for output. fstreams are generic files that you can do all file-related things with. (In fact, fstream inherits all of ifstream and all of ofstream! Excitement!)

well, nope, I would not flinch :-D but what I meant is different, somewhat.

I mean, sure I can pass objects, variabels and stuff, but when I open a file in one function, at the end the file is closed, isn't it? Thats what I meant, my stream-objects have function-scope and will be "vanished".

Ok, so within my one function "appendto_file()" I would use fstream instead of ifstream.

so, something like this??

Code:

---

std::fstream appendfile ( filename.c_str() );

string readtext;  // to print out the file-content
getline( appendfile, readtext );
std::cout << readtext;

std::string appendtext; // where the userinput goes into
std::getline ( std::cin, appendtext );
appendfile<<appendtext.c_str();
appendfile.closoe()

---

Quote:

---

I mean, sure I can pass objects, variabels and stuff, but when I open a file in one function, at the end the file is closed, isn't it? Thats what I meant, my stream-objects have function-scope and will be "vanished".

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Pass the objects by reference so they are not deconstructed (therefore the stream will not be closed).

hmm... I have no clue how to do that.

Also, I would have to check in every function, if the object is already created or not, if not: create it, if yes, work with it. But right now, I have no idea how ;-)

That was certainly not covered yet in any tutorial I read. A good feeling though, to leap ahead of tutorials (which I did anyway with this program).

What I mean is this:

Code:

---

int main(void)
{
    fstream f;
    // Set up the fstream
    foo(f);
}

void foo(fstream& f)
{
    // Do stuff with f here.  Since f was passed by reference, it will not be deleted when this
    // function ends.
}

---

Passing by reference means:

Code:

---

void foo(int& x) // Notice the & after int. That says it's a reference.
{
}

int x = 0;
foo(x);

---

When you pass by reference, no copy of the object is made (if you don't pass by reference, a local copy is constructed and the object you pass is copied).

And no, c_str() will not clear your string contents.

thanks guys :-) I will try that tomorrow, today I am out of here :-)

you are great :-)