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**File Operations in C++: Reading and Writing Files** Learn how to use file streams for reading and writing data in C+

File Streams, Insertion Operator, Extraction Operator, C-strings, std

nancyferrell
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**File Operations in C++: Reading and Writing Files** Learn how to use file streams for reading and writing data in C+

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  1. File Streams and File I/O

  2. Stream Operators • Insertion Operator ‘<<’ • As seen with cout << var • Extraction Operator ‘>>’ • As seen with cin >> var

  3. Stream Declarations #include <fstream> using namespace std; int main() { ifstream fin; // streams data from a file ofstreamfout; // streams data to a file

  4. Stream Declarations #include <fstream> using namespace std; int main() { ifstreamfin(“input.dat”); //connects this stream // to an existing data // file in the same // directory ofstream fout(“output.dat”); //creates a text file // in the same // directory

  5. Opening a File w/C-strings #include <iostream> #include <fstream> using namespace std; int main() { ifstream fin; ofstream fout; fin.open(“input.dat”); // !may not connect! fout.open(“output.dat”);

  6. Opening a File w/C-strings • File may not exist • File may be misspelled • Perhaps wrong directory • etc #include <iostream> #include <fstream> using namespace std; int main() { ifstream fin; ofstream fout; fin.open(“input.dat”); // !may not connect! fout.open(“output.dat”);

  7. Opening a File w/C-strings #include <iostream> #include <fstream> using namespace std; int main() { char file[20]; ifstream fin; do { fin.clear(); cout << “enter name of file to connect to: “; cin.getline(file, 20); fin.open(file); } while(!fin);

  8. Opening a File w/C-strings #include <iostream> #include <fstream> using namespace std; int main() { char file[20]; ifstream fin; do { fin.clear(); // clears the fail bit – allows retry cout << “enter name of file to connect to: “; cin.getline(file, 20); fin.open(file); } while(!fin);

  9. Opening a File w/C-strings #include <iostream> #include <fstream> using namespace std; int main() { char file[20]; ifstream fin; do { fin.clear(); // clears the fail bit – allows retry cout << “enter name of file to connect to: “; cin.getline(file, 20); fin.open(file); } while(!fin);

  10. Opening a File w/C-strings #include <iostream> #include <fstream> using namespace std; int main() { char file[20]; ifstream fin; do { fin.clear(); // clears the fail bit – allows retry cout << “enter name of file to connect to: “; cin.getline(file, 20); fin.open(file); } while(!fin);

  11. Opening a File w/C-strings #include <iostream> #include <fstream> using namespace std; int main() { char file[20]; ifstream fin; do { fin.clear(); // clears the fail bit – allows retry cout << “enter name of file to connect to: “; cin.getline(file, 20); fin.open(file); } while(!fin);

  12. Opening a File w/std::strings #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; do { fin.clear(); cout << “enter name of file to connect to: “; cin >> file; fin.open(file.c_str()); } while(!fin);

  13. Opening a File w/std::strings #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; do { fin.clear(); cout << “enter name of file to connect to: “; cin >> file; fin.open(file.c_str()); } while(!fin);

  14. Opening a File w/std::strings #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; do { fin.clear(); cout << “enter name of file to connect to: “; cin >> file; fin.open(file.c_str()); } while(!fin);

  15. Opening a File w/std::strings #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; do { fin.clear(); cout << “enter name of file to connect to: “; cin >> file; fin.open(file.c_str()); } while(!fin);

  16. Reading a File input.dat 3 -1 34 56 3 14 12 6 124 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; int num; ... // code for opening the file fin >> num; fin >> num; fin >> num; fin >> num; etc;

  17. Reading a File input.dat 3 -1 34 56 3 14 12 6 124 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; int num; ... // code for opening the file fin >> num; fin >> num; fin >> num; fin >> num; etc;

  18. Reading a File input.dat 3 -1 34 56 3 14 12 6 124 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; int num; ... // code for opening the file fin >> num; fin >> num; fin >> num; fin >> num; etc;

  19. Reading a File input.dat 3 -1 34 56 3 14 12 6 124 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; int num; ... // code for opening the file fin >> num; fin >> num; fin >> num; fin >> num; etc;

  20. Reading a File input.dat 3 -1 34 56 3 14 12 6 124 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; int num; ... // code for opening the file fin >> num; fin >> num; fin >> num; fin >> num; etc;

  21. Closing a File #include <iostream> #include <fstream> #include <string> using namespace std; int main() { string file; ifstream fin; int num; ... // code for opening the file ... // code for reading from the file fin.close();

  22. More Reads input.dat Price Clayton 12 Hurson Ali 41 Buechler Matt 87 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; int age; fin >> last; fin >> first; fin >> age; fin >> last; fin >> first; fin >> age; etc.

  23. More Reads input.dat Price Clayton 12 Hurson Ali 41 Buechler Matt 87 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; int age; fin >> last; fin >> first; fin >> age; fin >> last; fin >> first; fin >> age; etc.

  24. More Reads input.dat Price Clayton 12 Hurson Ali 41 Buechler Matt 87 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; int age; fin >> last; fin >> first; fin >> age; fin >> last; fin >> first; fin >> age; etc.

  25. More Reads input.dat Price Clayton 12 Hurson Ali 41 Buechler Matt 87 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; int age; fin >> last; fin >> first; fin >> age; fin >> last; fin >> first; fin >> age; etc.

  26. More Reads input.dat Price Clayton 12 Hurson Ali 41 Buechler Matt 87 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; int age; fin >> last; fin >> first; fin >> age; fin >> last; fin >> first; fin >> age; etc.

  27. More Reads input.dat Price Clayton 12 Hurson Ali 41 Buechler Matt 87 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; int age; fin >> last; fin >> first; fin >> age; fin >> last; fin >> first; fin >> age; etc.

  28. More Reads input.dat Price Clayton 12 Hurson Ali 41 Buechler Matt 87 #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; int age; fin >> last; fin >> first; fin >> age; fin >> last; fin >> first; fin >> age; etc.

  29. More Reads input.dat 51324 53 A Intro to Programming 51325 53 B Intro to Programming 51326 53 C Intro to Programming 51334 128 A Discrete Mathematics 51335 128 B Discrete Mathematics 51344 153 A Data Structures 51345 153 B Data Structures #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file intclass_num, course; char section; string title;

  30. More Reads input.dat 51324 53 A Intro to Programming 51325 53 B Intro to Programming 51326 53 C Intro to Programming 51334 128 A Discrete Mathematics 51335 128 B Discrete Mathematics 51344 153 A Data Structures 51345 153 B Data Structures #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file intclass_num, course; char section; string title;

  31. More Reads input.dat 51324 53 A Intro to Programming 51325 53 B Intro to Programming 51326 53 C Intro to Programming 51334 128 A Discrete Mathematics 51335 128 B Discrete Mathematics 51344 153 A Data Structures 51345 153 B Data Structures #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file intclass_num, course; char section; string title;

  32. More Reads input.dat 51324 53 A Intro to Programming 51325 53 B Intro to Programming 51326 53 C Intro to Programming 51334 128 A Discrete Mathematics 51335 128 B Discrete Mathematics 51344 153 A Data Structures 51345 153 B Data Structures #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file intclass_num, course; char section; string title;

  33. More Reads input.dat 51324 53 A Intro to Programming 51325 53 B Intro to Programming 51326 53 C Intro to Programming 51334 128 A Discrete Mathematics 51335 128 B Discrete Mathematics 51344 153 A Data Structures 51345 153 B Data Structures #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file intclass_num, course; char section; string title; fin >> class_num; fin >> course; fin >> section; getline(fin, title, ‘\n’);

  34. More Reads input.dat Price, Clayton Hurson, Ali Buechler, Matt Van Horn, Keith Walker, Betty Sue #include <iostream> #include <fstream> #include <string> using namespace std; int main() { ... // code for opening the file string last, first; getline(fin, last, ‘,’); getline(fin, first, ‘\n’); etc.

  35. End of Session

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