10/23/02 21:20:33 IO_Examples

Transcription

1 1 Oct 22 22: extractor1.c Page 1 istream &operator>>( istream &in, Point &p ){ char junk; in >> junk >> p.x >> junk >> p.y >> junk; return in;

2 2 Oct 22 22: extractor2.c Page 1 istream &operator>>( istream &in, Point &p ){ char junk; int ok; ok = FALSE; in >> junk; if( junk == ( ){ in >> p.x >> junk; if( junk ==, ){ in >> p.y >> junk; if( junk == ) ){ ok = TRUE; if(!ok ){ in.clear( in.rdstate() ios::failbit ); return in;

3 3 Oct 22 23: filenames.c Page 1 int n; for( n = 0; n < 1000; n += 1 ){ char filename[ 8 ]; ostrstream os( filename, 8 ); os << "file" << setw( 3 ) << setfill( 0 ) << n << ends; ifstream file( filename ); Process the data in the file

4 4 Oct 22 22: integer.c Page 1 Demonstrate formatted integer output #include <iostream.h> #include <iomanip.h> int main(){ char ruler[] = " "; int a( 5 ), b( ); Default settings cout << endl << ruler << endl; cout << a << << b << endl; Set minimum width to note how width is reset. cout << endl << ruler << endl; cout << setw( 10 ) << a << << b << endl; Set minimum width to 3 for each value. cout << endl << ruler << endl; cout << setw( 3 ) << a << << setw( 3 ) << b << endl; Change the fill character to $ cout << endl << ruler << endl; cout << setfill( $ ) << setw( 10 ) << a << << setw( 10 ) << b << endl; return 0; Output:

5 $$$$$$$$$5 $$$$$12345

6 6 Oct 22 23: input1.c Page 1 Process input that comes four values per line (1st attempt). #include <strstream.h> int main(){ char buffer[ 100 ]; Get and process one line of input. while( cin.getline( buffer, sizeof( buffer ) ) ){ istrstream is( buffer ); int a, b, c, d; cout << "\ninput is \"" << buffer << "\"" << endl; Try to extract four values. If this fails, the input is either bad or short. is >> a >> b >> c >> d; if(!is ){ cout << "Not enough values, or bad input" << endl; else { We got 4 values. If we re at eof, the input is correct, otherwise there are too many values. if( is.eof() ){ cout << "OK: a = " << a << ", b = " << b << ", c = " << c << ", d = " << d << endl; else { cout << "Too many values" << endl; ========= Output: =========

7 7 Input is "1 2 3" Not enough values, or bad input Input is " " OK: a = 1, b = 2, c = 3, d = 4 Input is " " Too many values Input is " " Too many values

8 8 Oct 22 23: input2.c Page 1 Process input that comes four values per line (final version). #include <strstream.h> int main(){ char buffer[ 100 ]; Get and process one line of input. while( cin.getline( buffer, sizeof( buffer ) ) ){ istrstream is( buffer ); int a, b, c, d; cout << "\ninput is \"" << buffer << "\"" << endl; Try to extract four values. If this fails, the input is either bad or short. is >> a >> b >> c >> d; if(!is ){ cout << "Not enough values, or bad input" << endl; else { We got 4 values. Try to skip whitespace to see if there is any more input. is >> ws; if( is ){ cout << "Too many values" << endl; else { cout << "OK: a = " << a << ", b = " << b << ", c = " << c << ", d = " << d << endl; ========== Output: ==========

9 9 Input is "1 2 3" Not enough values, or bad input Input is " " OK: a = 1, b = 2, c = 3, d = 4 Input is " " Too many values Input is " " OK: a = 1, b = 2, c = 3, d = 4

10 10 Oct 24 00: str-io-demo.c Page 1 id: str-io-demo.c Author: James Heliotis October 2000 This program demonstrates a skatload of things in C++ I/O: - opening files - reading and writing data using <<,>> - reading and writing data using other functions and C strings - I/O object failure - using I/O functions on strings via stringstreams #include <cstdlib> #include <iostream> #include <sstream> string streams #include <fstream> file streams #include <iomanip> I/O manipulators like setfill & setw using namespace std; const char END_LINE( \n ); const int ERR_NUMARGS( 1 ); bad # of command line arguments const int ERR_ARGFORMAT( 2 ); bad format of command line argument const int ERR_FILEACCESS( 3 ); file cannot be accessed main Echo the contents of a file to standard output. Arguments: #1: a number that is appended to the word "file" to get the file s name. The number is first extended to three digits. int main( int argc, char *argv[] ) { if ( argc!= 2 ) { cerr << "Usage: " << argv[0] << " file#" << endl; exit( ERR_NUMARGS ); Try to "read" the argument as an integer

11 11 istringstream is( argv[1] ); int n; is >> n; if ( is.fail() ) { cerr << "Usage: " << argv[0] << "file#" << endl; exit( ERR_ARGFORMAT ); If we get here the program was called with a single ineger arg.

12 12 Oct 24 00: str-io-demo.c Page 2 Open a string as an output stream in append mode. (There are easier ways to do this, but we re demoing!) ostringstream os( ios_base::app ios_base::out ); We will initialize the string to "file" and append the number. os.str( "file" ); os << setw( 3 ) << setfill( 0 ) << n << ends; Verify that the filename was created in the stream buffer. cout << "Now opening \"" << os.str() << " << endl; Open the file named file### for input. ifstream file( os.str().c_str() ); warning: only char* argument allowed (not std::string) if ( file.is_open() ) { Create a buffer to hold the data read. const unsigned int BUF_SIZE( 100 ); char buffer[ BUF_SIZE ]; Go into a loop loading and dumping the buffer. Normally, one uses is.read() with os.write(). file.getline( buffer, BUF_SIZE ); while(!file.eof() ) { cout.write( buffer, strlen(buffer) ); cout.put( END_LINE ); file.getline( buffer, BUF_SIZE ); else { file.close(); The file could not be opened.

13 13 cerr << string("no file named ") + os.str() + " exists, or it is unreadable.\n"; exit( ERR_FILEACCESS ); return 0;

14 14 Oct 22 22: inventory.c Page 1 Code snippets demonstrating random file access. ===== From the declaration of the Inventory class: friend class InventoryFile; private: Data members char name[ NAME_SIZE ]; Part name int quantity; Quantity on hand int price; Retail price of one part (etc.) ===== From the declaration of the InventoryFile class: private: Data members fstream file; unsigned int last_record_number; ===== From the implementation of the InventoryFile class: InventoryFile constructor InventoryFile::InventoryFile( char const *filename ): file( filename, ios::in ios::out ios::nocreate ){ if(!file ){ throw InventoryFileError( ERROR_OPENING_FILE ); last_record_number =...; read_part void InventoryFile::read_part( unsigned int part_number, Inventory &record ){ assert( part_number < last_record_number ); file.seekg( part_number * sizeof( record ), ios::beg ); file.read( record.name, sizeof( record ) ); if( file.gcount()!= sizeof( record ) ){ throw( InventoryFileError( TRUNCATED_RECORD ) );

15 15 write_part void InventoryFile::write_part( unsigned int part_number, Inventory &record ){ assert( part_number < last_record_number ); file.seekp( part_number * sizeof( record ), ios::beg ); file.write( record.name, sizeof( record ) );

16 16 Oct 23 20: Float_O/Float_O.h Page 1 Demonstrate formatted floating point output #ifndef RITCS_FLOAT_O_H #define RITCS_FLOAT_O_H class Float_O { private: output of floats with various styles public: ; Float_O #endif void output_line( double d ); void out_set( double d ); static void main();

17 17 Oct 23 21: Float_O/Float_O.C Page 1 Demonstrate formatted floating point output #include <iostream> #include <iomanip> #include <cmath> #include "Float_O.h" using namespace std; void Float_O::output_line( double d ){ cout << setw( 20 ) << d; cout << setw( 20 ) << setprecision( 10 ) << d; cout << setw( 20 ) << setiosflags( ios::showpoint ) << d << endl; cout << resetiosflags( ios::showpoint ) << setprecision( 6 ); void Float_O::out_set( double d ){ cout << setw( 11 ) << "" << setw( 20 ) << "Precision=6" << setw( 20 ) << "Precision=10" << setw( 20 ) << "showpoint" << endl; cout << setw( 11 ) << "Default:"; output_line( d ); cout << setw( 11 ) << "Fixed:" << setiosflags( ios::fixed ); output_line( d ); cout << resetiosflags( ios::fixed ); cout << setw( 11 ) << "Scientific:" << setiosflags( ios::scientific ); output_line( d ); cout << resetiosflags( ios::scientific ) << endl; void Float_O::main(){ Float_O f; Default settings f.out_set( 1 ); f.out_set( sqrt( 2 ) ); f.out_set( sqrt( 2 ) * 10 );

18 18 f.out_set( pow( 2, 26 ) );

19 19 Oct 23 21: Float_O/Float_O_Run.C Page 1 Demonstrate formatted floating point output #include "Float_O.h" int main() { Float_O::main(); return 0; Output: Precision=6 Precision=10 showpoint Default: Fixed: Scientific: e e e+00 Precision=6 Precision=10 showpoint Default: Fixed: Scientific: e e e+00 Precision=6 Precision=10 showpoint Default: Fixed: Scientific: e e e+01 Precision=6 Precision=10 showpoint Default: e Fixed: Scientific: e e e+07