C++ Primer Plus

File Modes

The file mode describes how a file is to be used: read it, write to it, append it, and so on. When you associate a stream with a file, either by initializing a file stream object with a filename or by using the open() method, you can provide a second argument that specifies the file mode:

ifstream fin("banjo", mode1);  // constructor with mode argumentofstream fout();fout.open("harp", mode2);      // open() with mode arguments

The ios_base class defines an openmode type to represent the mode; like the fmtflags and iostate types, it is a bitmask type. (In the old days, it was type int.) You can choose from several constants defined in the ios_base class to specify the mode. Table 17.7 lists the constants and their meanings. C++ file ...