Trouble with reading data with istringstream

Well, this stinks....I'm able to user ostringstream to wreite data to a file but when i read it back, Dev C++ gives me these errors:

Code:

Compiler: Default compiler
Building Makefile: "F:\Projects\Makefile.win"
Executing  make...
make.exe -f "F:\Projects\Makefile.win" all
g++.exe -c User.cpp -o User.o -I"F:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include"  -I"F:/Dev-Cpp/include/c++/3.4.2/backward"  -I"F:/Dev-Cpp/include/c++/3.4.2/mingw32"  -I"F:/Dev-Cpp/include/c++/3.4.2"  -I"F:/Dev-Cpp/include"   

User.cpp: In member function `bool User::loadUserFile(const char*)':
User.cpp:54: error: ambiguous overload for 'operator>>' in '((User*)this)->User::UserDataIn >> ((std::string*)this)->std::basic_string<_CharT, _Traits, _Alloc>::c_str [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]()'
F:/Dev-Cpp/include/c++/3.4.2/istream:687: note: candidates are: std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*) [with _Traits = std::char_traits<char>] <near match>
F:/Dev-Cpp/include/c++/3.4.2/istream:692: note:                 std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*) [with _Traits = std::char_traits<char>] <near match>

User.cpp:55: error: ambiguous overload for 'operator>>' in '((User*)this)->User::UserDataIn >> (((std::string*)((User*)this)) + 4u)->std::basic_string<_CharT, _Traits, _Alloc>::c_str [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]()'
F:/Dev-Cpp/include/c++/3.4.2/istream:687: note: candidates are: std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*) [with _Traits = std::char_traits<char>] <near match>
F:/Dev-Cpp/include/c++/3.4.2/istream:692: note:                 std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*) [with _Traits = std::char_traits<char>] <near match>

make.exe: *** [User.o] Error 1

Execution terminated

this is how i'm reading the data:

Code:

bool User::loadUserFile(const char* filename)
{
     char UBuff[256];
     
     sprintf(UBuff,"%s.user",filename);
     
     UserFileIn.open(UBuff,ios_base::binary );
     
     if(UserFileIn.is_open() )
     {
           UserDataIn >> UserName.c_str();
           UserDataIn >> Password.c_str();
           
           UserFileIn.read((char*)&UserDataIn,sizeof(UserDataIn));
           
           if(UserFileIn.is_open() )
           {
                                   UserFileIn.close();
           }
           return true;
     }
     else
     {
         return false;
     }
     return true;
}

Also how would i make it so when u typed the password u'd get this: "*"?

You don't want to call c_str() when reading into a string. Just read directly into it:

Code:

           UserDataIn >> UserName;
           UserDataIn >> Password;

There might be other issues there (like where/how are those variables declared and are you mixing binary and text based input?), but I think that's what this specific problem is. Note that if you get errors with that version, make sure you #include <string>.

>> Also how would i make it so when u typed the password u'd get this: "*"?
You have to use non-standard input functions to do that. I think kbhit might help but I don't remember for sure. It's a common question if you'd like to search the board for better answers.

Doing this gives me these errors:

Code:

Compiler: Default compiler
Building Makefile: "F:\Projects\Makefile.win"
Executing  make...
make.exe -f "F:\Projects\Makefile.win" all
g++.exe -c main.cpp -o main.o -I"F:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include"  -I"F:/Dev-Cpp/include/c++/3.4.2/backward"  -I"F:/Dev-Cpp/include/c++/3.4.2/mingw32"  -I"F:/Dev-Cpp/include/c++/3.4.2"  -I"F:/Dev-Cpp/include"   

g++.exe -c User.cpp -o User.o -I"F:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include"  -I"F:/Dev-Cpp/include/c++/3.4.2/backward"  -I"F:/Dev-Cpp/include/c++/3.4.2/mingw32"  -I"F:/Dev-Cpp/include/c++/3.4.2"  -I"F:/Dev-Cpp/include"   

User.cpp: In member function `bool User::loadUserFile(const char*)':
User.cpp:54: error: ambiguous overload for 'operator>>' in '((User*)this)->User::UserDataIn >> "User Name: "'
F:/Dev-Cpp/include/c++/3.4.2/istream:687: note: candidates are: std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*) [with _Traits = std::char_traits<char>] <near match>
F:/Dev-Cpp/include/c++/3.4.2/istream:692: note:                 std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*) [with _Traits = std::char_traits<char>] <near match>
User.cpp:55: error: ambiguous overload for 'operator>>' in '((User*)this)->User::UserDataIn >> "Password: "'
F:/Dev-Cpp/include/c++/3.4.2/istream:687: note: candidates are: std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*) [with _Traits = std::char_traits<char>] <near match>
F:/Dev-Cpp/include/c++/3.4.2/istream:692: note:                 std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*) [with _Traits = std::char_traits<char>] <near match>

make.exe: *** [User.o] Error 1

Execution terminated

this is what i'm doing:

Code:

UserDataIn >> "User Name: " >> UserName;
           UserDataIn >> "Password: " >>  Password;

doesw it matter if i don;t use the user name/password strings? the ones in the "" would that still load the data from the file? (Just trying to get this, sorry if u said this and i didn't understand.

I didn't quite understand your question. You don't want to add the "User Name: " to the code that reads in the strings. You're just reading from the file or from the user. If you want to prompt a user to type in their username, you might do something like this:

Code:

cout << "User Name: ";
cin >> UserName;

But if you really want the password to be covered with '*', then you'll have to use something different than input streams anyway because they only look at the input after it has been typed by the user and the user hits <enter>. By then it is too late the letters are already on the screen.

Heres a working example, pseudo code:

Code:

#include <iostream>
#include <fstream>

using namespace std;

void readfile ( const char * filepath )
{
  ifstream file ( filepath);

  while ( !file.eof() )
  {
      string line;
      
      getline(&line, 256);

      cout << line.c_str() << endl;
  }
}

Maybe I'm being hypercritical but that whole post is quite misleading. As a working example getline is written entirely wrong. The inexperienced might later ask: How does it know to read from the file you opened? Why is there a magic number? Why is line passed by pointer? That is also exactly why it fails as pseudo code; it leads to unnecessary confusion about what to do.Pseudo code that has nothing to do with the OP's problem, and doesn't explain the algorithm you wanted to show is bad pseudo code.

Never write pseudo code again. :|

CppProgrammer33, why not show us the code that you use to write to file, and/or tell us what is the file format? This will make it clear if your motivation for writing:

Code:

UserDataIn >> "User Name: " >> UserName;
UserDataIn >> "Password: " >>  Password;

is that you want to skip the "User Name: " portion of the file, or if it is merely an error made in desperation.

Originally Posted by iPromise

Heres a working example, pseudo code:

That looks like it is intended to be compilable C++, not pseudo code. As such, I must point out that it is wrong: you should not use eof() to control a loop like that, you should not be taking the address of line, and there is no need to use c_str().

Sorry guys, I coded that on the spot, here is a better example:

Code:

#include <string>
#include <iostream>
#include <ifstream>

using namespace std;

int main ()
{
   ifstream File("...");

   while ( !File.eof() )
   {
       string line;
       
       File >> line;

       cout << line << endl;
   }

   File.close();

   return 0;
}

This works fine for me, I use eof() because I am reading until the end of the file, I don't see how thats a problem.

Originally Posted by iPromise

Sorry guys, I coded that on the spot, here is a better example:

Code:

#include <string>
#include <iostream>
#include <ifstream>

using namespace std;

int main ()
{
   ifstream File("...");

   while ( !File.eof() )
   {
       string line;
       
       File >> line;

       cout << line << endl;
   }

   File.close();

   return 0;
}

This works fine for me, I use eof() because I am reading until the end of the file, I don't see how thats a problem.

Sorry, but it's still wrong, see here (it's more C focused but the concept still applies to C++). What you need to do is test the result of the read operation instead of testing for EOF. If the read fails then there was nothing more to read and you shouldn't enter the loop at all. Testing for EOF and using it to control the loop means you go through the loop one more time than you should resulting in unexpected behavior (for newbs at least) of the program.

Your example should simply be:

Code:

string line;
while ( File >> line )
{
    cout << line << endl;
}

@iPromise: You really don't need to manually close files. The destructor will take care of it for you. Good to remember.