String incorrect for output command target

This is a discussion on String incorrect for output command target within the C++ Programming forums, part of the General Programming Boards category; Ok, I'm back, and I have a new question. What am I doing wrong in this code? Code: int save() ...

  1. #1
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    String incorrect for output command target

    Ok, I'm back, and I have a new question. What am I doing wrong in this code?

    Code:
    int save()
    {
        char * filename;
        char * fileext = ".rpg";
        cout<<"Save game?\n";
        cin>>choice;
        if (choice=="yes" || choice=="y" || choice=="Y" || choice=="Yes" || choice=="yES" || choice=="YES" || choice=="YeS" || choice=="yEs" || choice=="YEs" || choice=="yeS")
        {
                          cout<<"Save filename?\n";
                          cin>>filename;
                          filename=filename+fileext;
                          std::ofstream output(filename);
                          output <<startpoint<<' '<<yourname<<' '<<hp<<' '<<weapon<<' '<<attack<<' '<<maxhp<<' '<<gold<<' '<<frags<<' '<<dmg<<' '<<block<<' '<<bow<<' '<<handgrenade<<' '<<broom<<' '<<rope<<' '<<grapple<<' '<<stairboots<<' '<<goldplate<<' '<<goldgoblet<<' '<<goldbowl<<' '<<goldflatware<<' '<<rockbuster<<' '<<bluessword<<' '<<smsand<<' '<<lgsand<<' '<<bacon<<' '<<rbeef<<' '<<bbqpork<<' '<<bbqbeef<<' '<<chicken<<' '<<steak<<' '<<apple<<' '<<pear<<' '<<plum<<' '<<pineapple<<' '<<peach<<' '<<papaya<<' '<<cheese<<' '<<candy<<' '<<beaten<<' '<<broomequip<<' '<<rockbusterequip<<' '<<bluesswordequip<<' '<<bowgive<<' '<<taken<<' '<<computer<<' '<<motherboard<<' '<<floppydrive<<' '<<harddisk<<' '<<compucase<<' '<<os<<' '<<rps<<' '<<calculate<<std::endl;
                          output.close();
                          cout<<"Game Saved.\n";
        }
        else
        {
        }
        system("pause");
    }
    It gives me an error about using the wrong data type. What am I doing wrong and how can I fix it?

  2. #2
    Registered User Kernel Sanders's Avatar
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    Which line is giving you that error

  3. #3
    Captain Crash brewbuck's Avatar
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    If you want your input to be treated in a case-insensitive way, then do it. Checking to see if the input is equal to "yeS" is dumb. Nobody will ever type that. Seriously.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  4. #4
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    Wait, i forgot that that was a modified version. For that code, the problematic line is:
    Code:
    filename=filename+fileext;
    The real form of the code is this, and the erroneous line is bold:

    Code:
    int save()
    {
        string filename;
        cout<<"Save game?\n";
        cin>>choice;
        if (choice=="yes" || choice=="y" || choice=="Y" || choice=="Yes" || choice=="yES" || choice=="YES" || choice=="YeS" || choice=="yEs" || choice=="YEs" || choice=="yeS")
        {
                          cout<<"Save filename?\n";
                          cin>>filename;
                          filename=filename+".rpg";
                          std::ofstream output(filename);
                          output <<startpoint<<' '<<yourname<<' '<<hp<<' '<<weapon<<' '<<attack<<' '<<maxhp<<' '<<gold<<' '<<frags<<' '<<dmg<<' '<<block<<' '<<bow<<' '<<handgrenade<<' '<<broom<<' '<<rope<<' '<<grapple<<' '<<stairboots<<' '<<goldplate<<' '<<goldgoblet<<' '<<goldbowl<<' '<<goldflatware<<' '<<rockbuster<<' '<<bluessword<<' '<<smsand<<' '<<lgsand<<' '<<bacon<<' '<<rbeef<<' '<<bbqpork<<' '<<bbqbeef<<' '<<chicken<<' '<<steak<<' '<<apple<<' '<<pear<<' '<<plum<<' '<<pineapple<<' '<<peach<<' '<<papaya<<' '<<cheese<<' '<<candy<<' '<<beaten<<' '<<broomequip<<' '<<rockbusterequip<<' '<<bluesswordequip<<' '<<bowgive<<' '<<taken<<' '<<computer<<' '<<motherboard<<' '<<floppydrive<<' '<<harddisk<<' '<<compucase<<' '<<os<<' '<<rps<<' '<<calculate<<std::endl;
                          output.close();
                          cout<<"Game Saved.\n";
        }
        else
        {
        }
        system("pause");
    }

  5. #5
    Registered User Kernel Sanders's Avatar
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    ofstream's constructor can take a char * (a C string), not a C++ string

    Code:
    std::ofstream output(filename.c_str);

  6. #6
    Kernel hacker
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    Quote Originally Posted by Kernel Sanders View Post
    Code:
    std::ofstream output(filename.c_str);
    Or more correctly:
    Code:
    std::ofstream output(filename.c_str());
    I would ask the "Save ?" this way:
    Code:
    do {
        cout<<"Save game?\n";
        cin>>choice;
    } while (toupper(choice[0]) != 'Y' && toupper(choice[0]) != 'N');
    if (toupper(choice[0] == 'Y')
       ... do saving.
    Now that will of course accept "Yeah", "Yo" or "yn" as "Yes", but I think that's acceptable. If you do not want to do that, then you probably should write a proper parser that takes a list of valid "commands" for a particular situation, and only returns when you get a valid one.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  7. #7
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    That helps, so I'll upgrade my games to do that. But how do I convert the string to a char? Or, in the first code I posted, append the extension to the filename?

  8. #8
    Registered User Kernel Sanders's Avatar
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    Append with the += operator and convert it to a C string char * with the c_str() function

  9. #9
    a_capitalist_story
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    Quote Originally Posted by brewbuck View Post
    As soon as you've formed an opinion, you're already wrong
    Holy crap, how did my wife get a Sr. SWE job???
    Last edited by rags_to_riches; 08-19-2008 at 03:43 PM. Reason: Fixed quote

  10. #10
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    Off topic, man...

    What is the syntax for the c_str() function?

  11. #11
    Registered User Kernel Sanders's Avatar
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    Quote Originally Posted by DarkAlex View Post
    Off topic, man...

    What is the syntax for the c_str() function?
    Code:
    string s("whatever");
    char *cs = s.c_str();
    Google is your friend

  12. #12
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    Code:
    char *cs = s.c_str();
    should of course be:
    Code:
    const char *cs = s.c_str();
    although you usually just pass it directly to the fstream function (or whatever legacy code requires the C style string).

  13. #13
    Registered User Kernel Sanders's Avatar
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    Quote Originally Posted by Daved View Post
    Code:
    char *cs = s.c_str();
    should of course be:
    Code:
    const char *cs = s.c_str();
    although you usually just pass it directly to the fstream function (or whatever legacy code requires the C style string).
    Off topic - can you recommend a good reference for C++'s const keyword? As a C programmer learning C++ const is one of my stumbling blocks

  14. #14
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    Maybe this: http://www.parashift.com/c++-faq-lit...rrectness.html

    Otherwise, just the recommended books.

    You might also try searching gotw and/or comp.lang.c++.moderated, although it might be difficult given that const can be used in many scenarios without actually explaining it.

  15. #15
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    It keeps giving me errors...

    Code:
    int save()
    {
        string filenameo;
        char * filename;
        do
        {
           cout<<"Save game?\n";
           cin>>choice;
        } while (toupper(choice[0]) != 'Y' && toupper(choice[0]) != 'N');
        if (toupper(choice[0] == 'Y'))
        {
                          cout<<"Save filename?\n";
                          cin>>filenameo;
                          filename=filenameo.c_str();
                          filename=filename+="rpg";
                          std::ofstream output(filename);
                          output <<startpoint<<' '<<yourname<<' '<<hp<<' '<<weapon<<' '<<attack<<' '<<maxhp<<' '<<gold<<' '<<frags<<' '<<dmg<<' '<<block<<' '<<bow<<' '<<handgrenade<<' '<<broom<<' '<<rope<<' '<<grapple<<' '<<stairboots<<' '<<goldplate<<' '<<goldgoblet<<' '<<goldbowl<<' '<<goldflatware<<' '<<rockbuster<<' '<<bluessword<<' '<<smsand<<' '<<lgsand<<' '<<bacon<<' '<<rbeef<<' '<<bbqpork<<' '<<bbqbeef<<' '<<chicken<<' '<<steak<<' '<<apple<<' '<<pear<<' '<<plum<<' '<<pineapple<<' '<<peach<<' '<<papaya<<' '<<cheese<<' '<<candy<<' '<<beaten<<' '<<broomequip<<' '<<rockbusterequip<<' '<<bluesswordequip<<' '<<bowgive<<' '<<taken<<' '<<computer<<' '<<motherboard<<' '<<floppydrive<<' '<<harddisk<<' '<<compucase<<' '<<os<<' '<<rps<<' '<<calculate<<std::endl;
                          output.close();
                          cout<<"Game Saved.\n";
        }
        else
        {
        }
        system("pause");
    }
    Erroneous lines are bold, and errors are:

    In function `int save()':
    508 invalid conversion from `const char*' to `char*'
    509 invalid operands of types `char*' and `const char[4]' to binary `operator+'
    509 in evaluation of `operator+=(char*, const char[4])'

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