1. Input/Output Streams, Part 2
Department of Computer and Information Science, School of Science, IUPUI
Input/Output Streams, Part 2
Dale Roberts, Lecturer
Computer Science, IUPUI
10/6/2019

2. Stream Manipulators
C++ provides various stream manipulators that perform formatting tasks:
setting widths, precision, filling, flushing streams, skipping white spaces, inserting new line, inserting a null character, etc.…..
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3. Integral Stream Base
Integers are normally represented as base 10 values.
To change the base in which integers are interpreted on a stream, insert different manipulators – hex, oct – to reset the stream to decimal insert dec.
The base of a stream may also be changed by the stream manipulator setbase, which takes one integer argument of 10, 8 or 16 to set the base.
As setbase takes an argument, it is called a parameterized stream manipulator – requires the inclusion of <iomanip.h> file
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4. Floating Point Precision
Controlling of the floating point precision (i.e., number of digits to the right side of the decimal point) is done by setprecision (manipulator) or precision (member function).
A call to these, sets the precision for all subsequent output operations until the next precision-setting call is made.
A call to precision without arguments returns the current precision setting.
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5. Field Width
The ios width member function sets the field width (i.e., the number of character positions in which a value should be output or the number of characters that should be input) and returns the previous width.
If values processed are smaller than the field width, fill characters are inserted as padding.
A value wider than the designated width will not be truncated – the full number is printed.
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6. Other Manipulators User-defined
Stream Format State Flags (specifies the kind of formatting to be performed during stream I/O operations)
trailing zeros, justification, padding, stream base, scientific notation, upper/lower cases, setting/resetting format flags, etc.
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7. File Streams Provides high level support for file operations in C++
Consists of three components:
fstream - allows both input and output
ifstream - allows only input
ofstream - allows only output
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8. Files -- fstream class Inherits from fstreambase and iostream classes
fstreambase inherits from ios class
iostream – inherits from istream and ostream classes
ifstream – inherits from fstreambase and istream classes
ofstream – inherits from fstreambase and ostream classes
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9. File Stream Functions Contains the following functions:
open() - opens the stream
close() - closes the stream
attach() - attaches the stream to file descriptor
setbuf() - set the stream buffer
rdbuf() - returns the pointer to stream buffer
str() - returns a pointer to the buffer array
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10. File Streams - Syntax Syntax fstream();
fstream(const char *sFileName, int nMode, int nProt = 0664);
fstream(filedesc fdif);
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11. File Processing Modes nMode can be any of the following:
ios::in - input processing
ios::out - output processing
ios::trunc - discard the file contents
ios::nocreate - the file must exist in order to write
ios::noreplace - cannot rewrite to an existing file
ios::binay - open the file in binary mode
ios::app - append the new data to the contents of the file
ios::ate - open the file for output and move to the end
ios::in|ios::out - both input and output
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12. File Protection Modes nProt can be one of the following:
filbuf::shcompat - compatibility share mode
filebuf::sh_none - no sharing
filebuf::sh_read - read sharing
filebuf::sh_write - write sharing
filebuf::sh_read|filebuf::sh_write - both read and write sharing
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13. File Streams - Example fstream my_file;
fstream myfile(“cs265.txt”, ios::in)
fstream myfile(“cs265.txt”, ios::out)
const int nMAX_SIZE = 256; char buf[nMAX_SIZE];
filedesc fdesc = my_file.fd();
fstream fs(fdesc);
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14. File Streams - open() Opens a file as a stream Syntax
void open(const char *sfile, int nMode, int nProt = 0664);
Usage
fstream my_file; my_file.open(“cs265.txt”, ios::out);
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15. File Streams - close() Close the opened file.
The stream’s error flag is cleared unless the close fails.
Syntax
void close()
Usage
my_file.close();
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16. File I/O - Example
#include<iostream.h> #include<fstream.h>
main() { // fIn and fOut are objects of class fstream fstream fIn, fOut; int nCnt = 0; //for byte count; char cCh;
//Open the file copy.in for reading fIn.open("copy.in", ios::in);
//Open the file copy.out for writing fOut.open("copy.out", ios::out);
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17. File I/O – Example contd…
//Until the end of file is reached, read from //the file and write it to the out file and echo on the screen. while(fIn.get(cCh)) { fOut.put(cCh); cout.put(cCh); //echo on terminal ++nCnt; }
//Write the final byte count cout << "[ " << nCnt << " ]" << endl; fOut << nCnt;
//Close the files fIn.close(); fOut.close();
return 0;}
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18. File I/O - Files copy.in abcd efg hi j copy.out abcd efg hi j 14
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