Thread: passing ios::flag as a parameter ..

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    passing ios::flag as a parameter ..

    I have function saveData() which writes to a text file. I would like to tell it whether to append ios::app or create new ios:ut ... How do i pass these flags as a parameter to saveData(...)?

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    C++ Witch laserlight's Avatar
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    One option is to have a std::ostream as the parameter. If you really want to open the file according to a filename and format flags then std::ios::fmtflags should be the type of the format flags parameter.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Quote Originally Posted by laserlight View Post
    One option is to have a std::ostream as the parameter. If you really want to open the file according to a filename and format flags then std::ios::fmtflags should be the type of the format flags parameter.
    should it be this?

    Code:
    void saveData(std::ios::fmtflags flag) 
    {
          	ofstream outfile;
    	char filename[MAX_PATH] = "contract.txt";
    	outfile.open(filename, flag);
    }

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    C++ Witch laserlight's Avatar
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    Quote Originally Posted by csonx_p
    should it be this?
    It is probably correct but if you really need the filename variable, it would be better to write it as:
    Code:
    char filename[MAX_PATH] = "contract.txt";
    ofstream outfile(filename, flag);
    Actually, if you need filename, why not make it a std::string?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Quote Originally Posted by laserlight View Post
    Actually, if you need filename, why not make it a std::string?
    because

    Code:
    void open ( const char * filename, ios_base::openmode mode = ios_base::out );

  6. #6
    C++ Witch laserlight's Avatar
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    Use the c_str() member function, e.g.,
    Code:
    std::string filename = "contract.txt";
    ofstream outfile(filename.c_str(), flag);
    EDIT:
    By the way, it looks like I got it wrong: the std::ios::fmtflags is for format flags (duh). On the other hand, the source you quoted gives std::ios_base:penmode, so perhaps you can try std::ios::openmode as the type.
    Last edited by laserlight; 01-05-2009 at 12:55 PM.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Officially An Architect brewbuck's Avatar
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    Quote Originally Posted by csonx_p View Post
    because

    Code:
    void open ( const char * filename, ios_base::openmode mode = ios_base::out );
    You can call c_str() on the string to get a char *...
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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