1. Lecture 14 Arguments, Classes and Files

2. Arguments

3. Classes (.h – header files)

4. Classes (.cpp – Source files)

5. Classes  A function in a class that does not have the classes scope in the implementation is out of scope and produces a linker error.  A function in scope is defined using :: (){…}  A class that uses another class which also makes use of that class can cause issues with cyclical dependency (a linker error)  One can avoid this problem with strict separation of implementation (definition) and declaration. This is made possible due to Forward Declarations.  It is generally good practice to use classes as pointers  E.g. Car* mCar = new Car();

6. Files  Files are used to  A file can be written or read as plain text or binary  Binary files are based on reading and writing bytes  http://www.eecs.umich.edu/courses/eecs380/HANDOUTS/cpp BinaryFileIO-2.html  You don’t need to know how to read/write binary files

7.  #include #include #include  class Student { private: int number; char name[50]; float gpa; public: Student(int n, const char *s, float g); void save(ofstream& of); void load(ifstream& inf); };

8.  void Student::save(ofstream& of) { of.write(&number, sizeof(number)); of.write(name, sizeof(name)); of.write(&gpa, sizeof(gpa)); }  void Student::load(ifstream& inf) { inf.read(&number, sizeof(number)); inf.read(name, sizeof(name)); inf.read(&gpa, sizeof(gpa)); }

9.  main() { Student me(11321, "Myself", 4.3); ofstream myfile; myfile.open("silly.dat", ios::binary | ios::out); me.save(myfile); myfile.close(); return(0); }

10. ReadingFiles  std::getline(input stream (istream&), string&)  std::getline(input stream (istream&), string&, char) //delimiter  ifstream.open(“file name”, mode)  Modes belong to the ios namespace  ios::in //open file for reading  ios::open //open file for writing  ios::binary //binary expected instead of text  ios::ate //output position at end of file  ios::app //append to file  ios::trunc //truncate discard previous file information

11. Modes cont.  Modes can be combined using the bitwise OR |  e.g. ios::in | ios::app OR ios::in | ios::app | ios::binary  Modes are set as default for file objects  ofstream – ios::out  ifstream – ios::in  fstream – ios::in | ios::out  close should be called when done with using the file object

12. File state flags  bad() – returns true of an operation fails such as writing to a device with not enough space  fail() – returns bad() but also returns true if a character is extracted instead of an expected integer from a file  eof() – returns true for reading a file when the file has reached the end  good() – Checks more state flags than bad(), mostly returns false

13. Exercise  Create a file loading and writing program which takes a two command line arguments. The first determines whether a file should be read, the second determines the file to be read or written to. Use cin to input data to the file and use cout to output data read from the file.