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Constructing Output Stream Objects 

If you use only the predefined cout, cerr, or clog objects, you do not need to construct an output stream. You must use constructors for:

You can construct an output file stream in one of two ways:

  • Use the default constructor, and then call the open member function.

    ofstream myFile; // Static or on the stack
    myFile.open( "filename" );
    
    ofstream* pmyFile = new ofstream; // On the heap
    pmyFile->open( "filename" );
    
  • Specify a filename and mode flags in the constructor call.

    ofstream myFile( "filename", ios_base::out);
    

To construct an output string stream, you can use one of two ostrstream constructors. One dynamically allocates its own storage, and the other requires the address and size of a preallocated buffer.

  • The dynamic constructor is used in the following way:

    char* sp;
    ostrstream myString;
    mystring << "this is a test" << ends;
    sp = myString.str();  // Get a pointer to the string
    

    The ends "manipulator" adds the necessary terminating null character to the string.

  • The constructor that requires the preallocated buffer is used in the following way:

    char s[32];
    ostrstream myString( s, sizeof( s ) );
    myString << "this is a test" << ends; // Text stored in s
    

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