File I/O in C++

Using Input/Output Files A computer file is stored on a secondary storage device (e.g., disk);is stored on a secondary storage device (e.g., disk); is permanent;is permanent; can be used to provide input data to a program or receive output data from a program, or both;can be used to provide input data to a program or receive output data from a program, or both; should reside in Project directory for easy access;should reside in Project directory for easy access; must be opened before it is used.must be opened before it is used.

General File I/O Steps Declare a file name variable Associate the file name variable with the disk file name Open the file Use the file Close the file

Using Input/Output Files stream - a sequence of characters stream - a sequence of characters interactive (iostream)interactive (iostream)  cin - input stream associated with keyboard.  cout - output stream associated with display. file (fstream)file (fstream)  ifstream - defines new input stream (normally associated with a file).  ofstream - defines new output stream (normally associated with a file).

Stream I/O Library Header Files Note: There is no “.h” on standard header files : Note: There is no “.h” on standard header files : iostream -- contains basic information required for all stream I/O operations iostream -- contains basic information required for all stream I/O operations iomanip -- contains information useful for performing formatted I/O with parameterized stream manipulators iomanip -- contains information useful for performing formatted I/O with parameterized stream manipulators fstream -- contains information for performing file I/O operations fstream -- contains information for performing file I/O operations strstream -- contains information for performing in-memory I/O operations (i.e., into or from strings in memory) strstream -- contains information for performing in-memory I/O operations (i.e., into or from strings in memory)

ios is the base class. ios is the base class. istream and ostream inherit from ios istream and ostream inherit from ios ifstream inherits from istream (and ios) ifstream inherits from istream (and ios) ofstream inherits from ostream (and ios) ofstream inherits from ostream (and ios) iostream inherits from istream and ostream (& ios) iostream inherits from istream and ostream (& ios) fstream inherits from ifstream, iostream, and ofstream fstream inherits from ifstream, iostream, and ofstream Classes for Stream I/O in C++

C++ streams #include #include int main (void) { //Local declarations //Local declarations ifstream fsIn; ifstream fsIn; ofstream fsOut; ofstream fsOut;... return 0; return 0;}

input_stream.open("numbers.dat") Stream handle Name Calling Object Dot Operator Member Function Name File Name Object and Member Functions

File I/O Example: Writing #include #include using namespace std; int main(void) { ofstream outFile(“fout.txt"); outFile << "Hello World!"; outFile.close(); return 0; }

File I/O Example: Writing #include #include using namespace std; int main(void) { ofstream outFile; outFile.open(“fout.txt”); outFile.open(“fout.txt”); outFile << “First line”; //behave just like cout outFile.close(); outFile<<“Another line”<<endl; //?? outFile<<“Another line”<<endl; //?? return 0; }

File I/O Example: Reading #include #include int main(void) { ifstream openFile(“data.txt"); //open a text file data.txt char ch; while(!OpenFile.eof()){OpenFile.get(ch); cout << ch; }OpenFile.close(); return 0; return 0;}

File I/O Example: Reading #include #include int main(void) { ifstream openFile(“data.txt"); //Declare and open a text file string line; while(!openFile.eof()){ getline(openFile,line);//fetch line from data.txt and put it in a string cout << line; }openFile.close(); return 0; return 0;}

File I/O Example: Reading #include #include int main(void) { ifstream openFile(“data.txt"); //open a text file data.txt string line; if(openFile.is_open()){ // if(openFile.is_open()){ //while(!openFile.eof()){ getline(openFile,line);//read a line from data.txt and put it in a string cout << line; } else{ else{ cout<<“File does not exist!”<<endl; cout<<“File does not exist!”<<endl; exit(1);} exit(1);} }openFile.close(); return 0; return 0;}

More Input File-Related Functions ifstream fsin; ifstream fsin; fsIn.open(const char[] fname) fsIn.open(const char[] fname) connects stream fsIn to the external file fname.connects stream fsIn to the external file fname. fsIn.get(char& character) fsIn.get(char& character) extracts next character from the input stream fsIn and places it in the character variable character.extracts next character from the input stream fsIn and places it in the character variable character. fsIn.eof() fsIn.eof() tests for the end-of-file condition.tests for the end-of-file condition.

More Output File-Related Functions ofstream fsOut; ofstream fsOut; fsOut.open(const char[] fname) fsOut.open(const char[] fname) connects stream fsOut to the external file fname.connects stream fsOut to the external file fname. fsOut.put(char character) fsOut.put(char character) inserts character character to the output stream fsOut.inserts character character to the output stream fsOut. fsOut.eof() fsOut.eof() tests for the end-of-file condition.tests for the end-of-file condition.

File Open Mode NameDescription ios::inOpen file to read ios::outOpen file to write ios::appAll the date you write, is put at the end of the file. It calls ios::out ios::ateAll the date you write, is put at the end of the file. It does not call ios::out ios::truncDeletes all previous content in the file. (empties the file) ios::nocreateIf the file does not exists, opening it with the open() function gets impossible. ios::noreplaceIf the file exists, trying to open it with the open() function, returns an error. ios::binaryOpens the file in binary mode.

File Open Mode #include int main(void) { ofstream outFile("file1.txt", ios::out); outFile << "That's new!\n"; outFile.close(); Return 0; } If you want to set more than one open mode, just use the OR operator- |. This way: ios::ate | ios::binary

Dealing with Binary files Functions for binary file handling Functions for binary file handling get(): read a byte and point to the next byte to read get(): read a byte and point to the next byte to read put(): write a byte and point to the next location for write put(): write a byte and point to the next location for write read(): block reading read(): block reading write(): block writing write(): block writing

Dealing with Binary files Some useful functions Some useful functions seekg(): Go to a specific position when reading seekg(): Go to a specific position when reading seekp(): Go to a specific position when writing seekp(): Go to a specific position when writing tellg() : Retunrs an int type, that shows the current position of the inside-pointer. This one works only when you read a file. tellg() : Retunrs an int type, that shows the current position of the inside-pointer. This one works only when you read a file. tellp(): The same as tellg() but used when we write in a file. tellp(): The same as tellg() but used when we write in a file. flush(): Save data from the buffer to the output file. flush(): Save data from the buffer to the output file.

Binary File I/O Examples // Example 1: Using get() and put() #include void main() { fstream File("test_file",ios::out | ios::in | ios::binary); char ch; ch='o'; File.put(ch); //put the content of ch to the file File.seekg(ios::beg); //go to the beginning of the file File.get(ch); //read one character cout << ch << endl; //display it File.close(); }

Binary File I/O Examples //Example 2: Using read() and write() #include #include void main() { fstream File("test_file.txt",ios::out | ios::in | ios::binary); char arr[13]; strcpy(arr,"Hello World!"); //put Hello World! into the array File.write(arr,5); //put the first 5 symbols into the file- "Hello" File.seekg(ios::beg); //go to the beginning of the file static char read_array[10]; //I will put the read data, here File.read(read_array,3); //read the first 3 symbols- "Hel" cout << read_array << endl; //display them File.close();}

More Binary File I/O Examples #include void main() { //if we have "Hello" in test_file.txt ifstream File("test_file.txt"); char arr[10]; File.read(arr,10); //this should return 5, as Hello is 5 characters long cout << File.tellg() << endl; File.close(); }

Summary of Input File-Related Functions #include #include ifstream fsIn; fsIn.open(const char[] fname) fsIn.open(const char[] fname) connects stream fsIn to the external file fname.connects stream fsIn to the external file fname. fsIn.get(char& c) fsIn.get(char& c) extracts next character from the input stream fsIn and places it in the character variable c.extracts next character from the input stream fsIn and places it in the character variable c. fsIn.eof() fsIn.eof() tests for the end-of-file condition.tests for the end-of-file condition. fsIn.close() fsIn.close() disconnects the stream and associated file.disconnects the stream and associated file. fsIn >> c; //Behaves just like cin fsIn >> c; //Behaves just like cin

Summary of Output File-Related Functions #include #include ofstream fsOut; fsOut.open(const char[] fname) fsOut.open(const char[] fname) connects stream fsOut to the external file fname.connects stream fsOut to the external file fname. fsOut.put(char c) fsOut.put(char c) inserts character c to the output stream fsOut.inserts character c to the output stream fsOut. fsOut.eof() fsOut.eof() tests for the end-of-file condition.tests for the end-of-file condition. fsOut.close() fsOut.close() disconnects the stream and associated file.disconnects the stream and associated file. fsOut << c; //Behaves just like cout fsOut << c; //Behaves just like cout