Embedded Files
Text File Streams
Text File Streams
#include <fstream>
#include <fstream>
#include <string>
#include <string>
using namespace std;
using namespace std;
int main()
int main()
{
{
ifstream input_fstream; // declare an input file stream
ifstream input_fstream; // declare an input file stream
ofstream output_fstream; // declare an output file stream
ofstream output_fstream; // declare an output file stream
string first_name, last_name;
string first_name, last_name;
inData.open("names.txt"); // open input file
inData.open("names.txt"); // open input file
outData.open("marks.txt"); // open output file
outData.open("marks.txt"); // open output file
inData >> firstName >> lastName; // read from a file stream
inData >> firstName >> lastName; // read from a file stream
outData << 85.6; // write into a file stream
outData << 85.6; // write into a file stream
inData.close(); // close the input file
inData.close(); // close the input file
outData.close(); // close the output file
outData.close(); // close the output file
return 0;
return 0;
}
}
Unbounded File Streams
Unbounded File Streams
On the previous section we opened an input stream, and we opened an output stream.
We could have used fstream, an unbounded file stream allowing both reading and writing.
fstream fstrm;
fstrm.open(s, mode);
Modes, for this and the I/O versions, partially:
in, out, app, ate, trunc, binary
Multiple modes can be set. They are part of fstream::
app: Always write at the end.
ate: On opening go the end.
trunc: Wipes out existing content.
binary: Doesn’t have the text conversion layer, you read/write in binary.
There are constraints on these flags. Some examples:
out is for fstream or ofstream.
trunc can only be set if out is.
app and trunc are mutually exclusive.
fstream unbounded_file;
fstream unbounded_file;
unbounded_file.open(outFileName, ios::in|ios::binary);
unbounded_file.open(outFileName, ios::in|ios::binary);
char * memblock;
char * memblock;
streampos fsize;
streampos fsize;
if (unbounded_file.is_open()) {
if (unbounded_file.is_open()) {
cout << "Is open" << endl;
cout << "Is open" << endl;
fsize = unbounded_file.tellg();
fsize = unbounded_file.tellg();
char * memblock = new char [fsize];
char * memblock = new char [fsize];
unbounded_file.seekg(0, ios::beg);
unbounded_file.seekg(0, ios::beg);
unbounded_file.read(memblock, fsize);
unbounded_file.read(memblock, fsize);
delete [] memblock;
delete [] memblock;
}
}
/*
/*
string line;
string line;
while (getline(unbounded_file, line))
while (getline(unbounded_file, line))
cout << line << endl;
cout << line << endl;
*/
*/
unbounded_file.close();
unbounded_file.close();
Errors in Opening Files
Errors in Opening Files
Don’t assume a file stream has been opened successfully.
Incorrect file name:
inFile.open("names.txl");
Incorrect file opening mode:
ifstream inFile;
inFile.open("names.txt", ios::trunc);
Not enough room on the hard drive.
Hardware failure.
Always check the status of a stream after open.
#include <fstream>
#include <fstream>
using namespace std;
using namespace std;
int main()
int main()
{
{
ifstream inData; // declare an input file stream
ifstream inData; // declare an input file stream
char fileName[] = "exams.txt";
char fileName[] = "exams.txt";
string lastName, mark;
string lastName, mark;
inData.open( fileName ); // open input file
inData.open( fileName ); // open input file
if (!inData) { // check if opened successfully
if (!inData) { // check if opened successfully
cerr << "Error opening : " << filename << endl;
cerr << "Error opening : " << filename << endl;
return -1; // exit with an error code
return -1; // exit with an error code
}
}
inData >> lastName >> mark;
inData >> lastName >> mark;
inData.close(); // Close the input file
inData.close(); // Close the input file
return 0;
return 0;
}
}
Errors in Reading Files
Errors in Reading Files
So the file seemed to open okay but being pessimistic, what goes wrong next.
The program may not have data to read as it hits the end of file.
The data may be invalid: ... an alphabetic character instead of a digit character; a control character instead of an alphabetic one; etc.
The data may not be physically accessed from the disk due to its damage or network failure.
Any illegal operation with a stream switches it to the Error State !
Any illegal operation with a stream switches it to the Error State !
Page updated
Google Sites
Report abuse