CIS 250 - File I/O

Objectives

• use C++ text file I/O
• use C++ binary file I/O

File I/O - text

• steps to using a file in C++:
  • include fstream header file
  • declare file stream variables
  • associate variable with I/O sources
  • use variables with >>, <<, and other functions
  • close the streams
• #include <fstream>
• declaring an input file variable: ifstream ifile;
• opening an input file: ifile.open("myfile"); (file must exist)
• combining declaration and opening: ifstream ifile("myfile");
• output works much like input: ofstream ofile("myfile");
• opening an output file for appending: ofile.open("myfile", ios::app); (file must exist)
• use standard stream operators and functions:
  • ofile << num1 << " " << num2 << endl;
  • ifile >> num1 >> num2;
• close fstreams when done: ifile.close()
• check for open failure: if (!ifile)
• check for end of file input: while (ifile)
• see fileio1.cpp for some sample file I/O code

File I/O - binary

• specify binary when opening file: ofstream ofile("testfileio2.txt", ios::binary);
• use write function to write data: ofile.write(reinterpret_cast<char *>(&n), sizeof(n));
• use read function to read data: ifile.read(reinterpret_cast<char *>(&n), sizeof(n));
• seek to end of file (reading): ifile.seekg(0L, ios::end);
• seek to beginning of file (reading): ifile.seekg(0L, ios::beg);
• seek 10 bytes further relative to current position (reading): ifile.seekg(10L, ios::cur);
• get postion in file (reading): ifile.tellg()
• position at end of file is length in bytes
• determine number of records by dividing file size by record size
• seekp and tellp are for write pointer
• see fileio2.cpp for some sample binary file I/O code
• see fileio3.cpp for some sample random access file I/O code