C++ Programming: chapter 6 – iostream 2015, Spring Pusan National University Ki-Joune Li 1

PNU fstream, ofstream, ifstream classes // reading a text file #include using namespace std; int main () { string line; ifstream myfile ("example.txt”, ios::in); if (myfile.is_open()) { while ( myfile.good() ) { getline (myfile,line); cout << line << endl; } myfile.close(); } else cout << "Unable to open file”; return 0; }

PNU 3 FlagExplanations ios::inOpen for input operations. ios::outOpen for output operations. ios::binaryOpen in binary mode. ios::ateSet the initial position at the end of the file. If this flag is not set to any value, the initial position is the beginning of the file. ios::appAll output operations are performed at the end of the file, appending the content to the current content of the file. This flag can only be used in streams open for output-only operations. ios::truncIf the file opened for output operations already existed before, its previous content is deleted and replaced by the new one. ofstream myfile; myfile.open ("example.bin", ios::out | ios::app | ios::binary);

PNU Checking File Status 4 functionsExplanations bad()returns true if a reading or writing operation fails fail()returns true in the same cases as bad(), but also in the case that a format error happens, like when an alphabetical character is extracted when we are trying to read an integer number. eof()returns true if a file open for reading has reached the end. good()returns false in the same cases in which calling any of the previous functions would return true.

PNU Set Position: tell and seek in C-language 5 #include using namespace std; int main () { long begin,end; ifstream myfile ("example.txt"); begin = myfile.tellg(); myfile.seekg (0, ios::end); end = myfile.tellg(); myfile.close(); cout << "size is: " << (end-begin) << " bytes.\n"; return 0; } functionsExplanations pos_type tellg(), pos_type tellp() Offset (g: for input file, p: for output file stream) seekg(pos_typ), seekp(pos_typ) Set position from the beginning seekg(pos_typ, direction) seekp(pos_typ, direction) Set position with direction ios::begoffset from the beginning ios::curoffset from the current ios::endoffset from the end

PNU Binary file i/o stream: read and write in C-Language 6 // reading a complete binary file #include using namespace std; ifstream::pos_type size; char * memblock; int main () { ifstream file ("example.bin", ios::in | ios::binary | ios::ate); if (file.is_open()) { size = file.tellg(); memblock = new char [size]; file.seekg (0, ios::beg); file.read(memblock, size); file.close(); cout << "the complete file content is in memory"; delete[] memblock; } else cout << "Unable to open file"; return 0; }

PNU Set flag: set flags for output stream 7 #include using namespace std; int main () { cout.setf(ios::hex, ios::basefield ); // set hex as the basefield cout << 100 << endl; cout.setf(ios::dec, ios::basefield ); // set decimal as the basefield cout.setf(ios::scientific); cout.precision(2); cout<< ; return 0; } format flag valuemask field bitmask left, right or internaladjustfield dec, oct or hexbasefield scientific or fixedfloatfield

PNU IOS hierarchy 8