Input / Output and the OS

Declarations and Initializations

char c = ‘A’, s[] = “Blue moon!”;

Format Printed Remarks

%c “A ” field width 1 by default

%2c “ A” field width 2, right adjusted

%-3c “A ” field width 3, left adjusted

%s “Blue moon!” field width 10 by default

%3s “Blue moon!” more space is needed

%.6s “Blue m” precision 6

%-11.8s “Blue moo ” precision 8, left adjusted

Declarations and Initializations

int i = 123;

double x = 0.123456789;

Format Printed Remarks

%d “123” field width 3 by default

%05d “00123” padded with zeros

%7o “ 173” right adjusted, octal

%-9x “7b ” left adjusted, hexadecimal

%-9#x “0x7b ” left adjusted, hexadecimal

%10.5f “ 0.12346” field width 10, precision 5

%-12.5e “1.23457e-01” left adjusted, e-format

Input and Output functionsfprintf(), fscanf(), sprintf(), sscanf()

stdin standard input file connected to the keyboard

stdout standard output file connected to the screen

stderr standard error file connected to the screen

int fprintf( FILE *fp, const char *format, ...);

int fscanf( FILE *fp, const char *format, ...);

fprintf( stdout, ... ); printf( ....);

fscanf( stdint, ...); scanf( .... );is equivalent tois equivalent to

sprintf and sscanf

int sprintf(char *s , const char *format, ...);

int sscanf(const char *s, const char *format, ...);

sprintf and sscanf

char str1[] = “1 2 3 go”, str2[100], tmp[100];

int a = 0, b = 0, c = 0;

sscanf( str1, “%d%d%d%s”, &a, &b, &c, tmp);

sprintf( str2, “%s %s %d %d %d\n”, tmp, tmp, a, b, c);

printf( “%s”, str2 );

output:

go go 1 2 3

scan from the string into the variables

scan from the string into the variables

print into the stringprint into the string

print the string to the screenprint the string to the screen

Working with Files#include <stdio.h>

int main( void )

{

int a = 0, sum = 0;

FILE *ifp = NULL, *ofp = NULL;

ifp = fopen( “my_file”, “r” );

ofp = fopen( “outfile”, “w”);

.....

while ( fscanf( ifp, “%d”, &a ) == 1 )

sum += a;

fprintf( ofp, “The sum is %d. \n”, sum );

....

fclose( ifp );

fclose( ofp );

}

file pointersfile pointers

open the files for reading / writing

open the files for reading / writing

close the filesclose the files

Double Spacing a File#include <stdio.h>

#include <stdlib.h>

void double_space( FILE *, FILE * );

void prn_info( char * );

void prn_err_msg( char * );

int main( int argc, char **argv )

{

int rtVal = 0;

FILE *ifp, *ofp;

if ( argc == 3 )

{

make sure that we got all the input parameters

make sure that we got all the input parameters

the return valuethe return value

Double Spacing a File

ifp = fopen( argv[1], “r” );

if ( ifp != NULL )

{

ofp = fopen( argv[2], “w” );

if ( ofp != NULL )

{

double_space(ifp, ofp);

fclose(ofp);

}

else rtVal = 3;

fclose(ifp);

}

else rtVal = 2;

}

make sure the input file is openmake sure the input file is open

make sure the output file is openmake sure the output file is open

mark the error type (which file did not open ... )

mark the error type (which file did not open ... )

Double Spacing a File

else

{

rtVal = 1;

prn_info( argv[0] );

}

if ( rtVal > 1 )

prn_err_msg( argv[ 2 ] );

return rtVal;

}

the else of ( argc == 3 )the else of ( argc == 3 )

file not open error messagefile not open error message

Double Spacing a File

void prn_info( char *pgm_name )

{

printf( “\n%s%s%s\n\n%s%s\n\n”,

“Usage: ”, pgm_name, “ infile outfile”,

“The contents of infile will be double-spaced ”,

“and written to outfile.” );

}

void prn_err_msg( char *file_name )

{

printf( “\n%s%s\n\n”, “Error – could not open file ”, file_name );

}

Double Spacing a File

void double_space( FILE *ifp, FILE *ofp )

{

int c = 0;

while ( ( c = getc( ifp ) ) != EOF )

{

putc( c, ofp );

if ( c == ‘\n’ )

putc( ‘\n’ , ofp );

}

}

found a new line, duplicate itfound a new line, duplicate it

Replicating a File with Caps#include <stdio.h>

#include <stdlib.h>

#include <ctype.h>

FILE* gfopen( char* file_name, char* mode);

int main( int argc, char **argv )

{

int c = 0;

FILE *fp = NULL, *tmp_fp = NULL;

if ( argc != 2 )

{

fprintf(stderr, “\n%s%s%s\n\n%s\n\n”, “Usage: ”, argv[0], “ file_name”,

“The file will be doubled and some letters capitalized.” );

exit(1);

}

fp = gfopen( argv[1], “r+” );

tmp_fp = tmpfile();

while ( ( c = getc( fp ) ) != EOF )

putc( toupper( c ), tmp_fp );

rewind( tmp_fp );

fprintf( fp, “---\n” );

while ( ( c = getc( tmp_fp ) ) != EOF )

putc( c, fp );

return 0;

}

Replicating a File with Caps

Replicating a File with Caps

FILE* gfopen( char* file_name, char* mode )

{

FILE *fp = NULL;

if ( ( fp = fopen( file_name, mode ) ) == NULL )

{

fprintf( stderr, “Cannot open %s - bye!\n”, file_name );

exit(1);

}

return fp;

}

not always the best idea, this could leave behind allocated

memory and open files ... but you get the general idea

not always the best idea, this could leave behind allocated

memory and open files ... but you get the general idea

Results

in file apple: A is for apple and alphabet pie.

command: replicate_with_caps apple

output:

A is for apple and alphabet pie

---

A IS FOR APPLE AND ALPHABET PIE

fseek

fseek(file_ptr, offset, place);

#define SEEK_SET 0

#define SEEK_CUR 1

#define SEEK_END 2

ftell(file_ptr);

beginning of the filebeginning of the file

current position in the filecurrent position in the file

end of the fileend of the file

Write a File Backwards

#include <stdio.h>

#define MAXSTRING 100

int main( void )

{

char file_name[MAXSTRING] = { 0 };

int c = 0;

FILE *ifp = NULL;

fprintf( stderr, “\nInput a file name: ” );

scanf( “%s”, file_name );

ifp = fopen( file_name, “rb” ); binary mode for ms-dosbinary mode for ms-dos

Write a File Backwards

fseek( ifp, 0, SEEK_END );

fseek( ifp, -1, SEEK_CUR );

while ( ftell( ifp ) >= 0 )

{

c = getc( ifp );

putchar( c );

fseek( ifp, -2, 1 );

}

return 0;

}

move to the end of the filemove to the end of the file

back up one characterback up one character

move ahead one charactermove ahead one character

back up two charactersback up two characters

Change the Case of Letters in a File

#include <ctype.h>

#include <fcntl.h>

#include <unistd.h>

#define BUFSIZE 1024

int main(int argc, char **argv)

{

char mybuf[BUFSIZE] = { 0 }, *p = NULL;

int in_fd = 0, out_fd = 0, n = 0;

in_fd = open( argv[1], O_RDONLY );

out_fd = open( argv[2], O_WRONLY | O_EXCL | O_CREAT, 0600 );

use io.h in ms-dosuse io.h in ms-dos

open fileopen file

file permissionsfile permissions

Change the Case of Letters in a File

while ( ( n = read( in_fd, mybuf, BUFSIZE ) ) > 0 )

{

for ( p = mybuf; p - mybuf < n; ++p )

{

if ( islower( *p ) ) *p = toupper(*p);

else if ( isupper( *p ) ) *p = tolower(*p);

}

write( out_fd, mybuf, n );

}

close( in_fd );

close( out_fd );

return 0;

}

write and close filewrite and close file

File Permissionsr-- 100 04-w- 010 02--x 001 01rw- 110 06r-x 101 05-wx 011 03rwx 111 07

++++++

rw------- 0600rw----r-- 0604rwxr-xr-x 0755rwxrwxrwx 0777

File Open Flag Options

O_CREAT

O_EXCL

O_NOCTTY

O_TRUNC

O_APPEND

O_NONBLOCK

O_NDELAY

O_SYNC

O_NOFOLLOW

O_DIRECTORY

O_LARGEFILE

Direct Input / Output

int fread(void *a_ptr, int el_size, int n, FILE *fp);

int fwrite(void *a_ptr, int el_size, int n, FILE *fp);

used to read and write binary files, no conversions are performedused to read and write binary files, no conversions are performed

Change the Case of Letters in a File

#include <ctype.h>

#include <stdio.h>

#define BUFSIZE 1024

int main(int argc, char **argv)

{

char mybuf[BUFSIZE] = { 0 }, *p = NULL;

FILE *ifd = NULL, *ofd = NULL;

int n = 0;

ifp = fopen( argv[1], “r” );

ofp = fopen( argv[2], “w” );

open the file for readingopen the file for reading

open the file for writingopen the file for writing

Change the Case of Letters in a File

while ( ( n = fread( ifd, mybuf, BUFSIZE ) ) > 0 )

{

for ( p = mybuf; p - mybuf < n; ++p )

{

if (islower(*p)) *p = toupper(*p);

else if (isupper(*p)) *p = tolower(*p);

}

fwrite(ofd, mybuf, n);

}

fclose(ifd);

fclose(ofd);

return 0;

}

read from the fileread from the file

write to the filewrite to the file

close the filesclose the files

Write only Lowercase on Screen

#include <stdio.h>

#include <stdlib.h>

#include <ctype.h>

#define MAXSTRING 100

int main( void )

{

char command[MAXSTRING] = { 0 }, *tmp_filename = NULL;

int c = 0;

FILE *ifp = NULL;

tmp_filename = tmpnam( NULL );

sprintf( command, “dir > %s”, tmp_filename );

create a temporary file namecreate a temporary file name

Write only Lowercase on Screen

system( command );

ifp = fopen( tmp_filename, “r” );

while ( ( c = getc( ifp ) ) != EOF )

putchar( tolower( c ) );

remove( tmp_filename );

return 0;

}

execute the system commandexecute the system command

remove the temporary fileremove the temporary file

#include <ctype.h>

#include <stdio.h>

int main( void )

{

int c = 0;

FILE *ifp = NULL;

ifp = popen( “ls”, “r” );

while ( ( c = getc( ifp ) ) != EOF )

putchar( toupper( c ) );

pclose( ifp );

return 0;

}

Profiling

#include <stdio.h>

#include <stdlib.h>

#include <time.h>

#define N 50000

void quicksort(int *, int *);

int main(void)

{

int a[N] = { 0 }, i = 0;

srand( time( NULL ) );

for ( i = 0; i < N; ++i )

a[i] = rand() % 10000;

seed the random functionseed the random function

create a number between 0 and 9999create a number between 0 and 9999

Profiling

quicksort( a, a + N – 1 );

for ( i = 0; i < N - 1; ++i )

{

if ( a[i] > a[i + 1] )

{

printf( “SORTING ERROR - bye!\n” );

exit( 1 );

}

}

return 0;

}

Profiling

cc -p -o quicksort main.c quicksort.c

quicksort→mon.out

prof quicksort

% time cumsecs #call ms / callname func name

46.9 7.18 9931 0.72 _partition

12.1 9.64 1 2460.83 _main

11.7 11.43 19863 0.09 _find_pivot

… … … … …

0.0 15.33 1 0.0 _time

Timing Functions

#include <stdio.h>

#include <stdlib.h>

#include <time.h>

clock_t clock(void);

#define CLOCKS_PER_SEC 60

time_t time(time_t *p);

double difftime(time_t, time_t);

time used by the machinetime used by the machine

machine dependentmachine dependent

seconds since 1970seconds since 1970

Timing Functions#include <stdio.h>

#include <stdlib.h>

#include <time.h>

#define MAXSTRING 100

typedef struct

{

clock_t begin_clock, save_clock;

time_t begin_time, save_time;

} time_keeper;

static time_keeper tk;

void start_time(void)

{

tk.begin_clock = tk.save_clock = clock();

tk.begin_time = tk.save_time = time(NULL);

}

known only to this fileknown only to this file

Timing Functions

double prn_time(void)

{

char s1[MAXSTRING] = { 0 }, s2[MAXSTRING] = { 0 };

int field_width = 0, n1 = 0, n2 = 0;

double clocks_per_second = (double) CLOCKS_PER_SEC,

user_time = 0, real_time = 0;

user_time = ( clock() - tk.save_clock ) / CLOCKS_PER_SEC;

real_time = difftime( time( NULL ), tk.save_time );

tk.save_clock = clock();

tk.save_time = time(NULL);

Timing Functions

n1 = sprintf( s1, “%.2f”, user_time );

n2 = sprintf( s2, “%.2f”, real_time );

printf( “ s1=%s n1=%d\n”, s1, n1 );

printf( “ s2=%s n2=%d\n”, s2, n2 );

field_width = ( n1 > n2 ) ? n1 : n2;

printf( “%s%*.2f%s\n%s%*.2f%s\n\n”,

“User time: ”, field_width, user_time, “ seconds”,

“Real time: ”, field_width, real_time, “ seconds” );

return user_time;

}

print the values found, and do it neatly

print the values found, and do it neatly

Compare float and double multiplication times

#include <stdio.h>

#include "u_lib.h"

#define N 100000000

int main(void)

{

long i = 0;

float a = 0, b = 3.333, c = 5.555;

double x = 0, y = 3.333, z = 5.555;

printf( “Number of multiplies: %d\n\n”, N );

printf( “Type float:\n\n” );

one hundred millionone hundred million

arbitrary valuesarbitrary values

Compare float and double multiplication times

start_time();

for ( i = 0; i < N; ++i )

a = b * c;

prn_time();

printf( “Type double:\n\n” );

for ( i = 0; i < N; ++i )

x = y * z;

prn_time();

return 0;

}

Compare float and double multiplication times

Number of multiplies: 100000000

Type float:

User time: 33.6 seconds

Real time: 34.0 seconds

Type double:

User time: 33.5 seconds

Real time: 33.0 seconds

#include <stdio.h>

int main( int argc, char *argv[], char *env[] )

{

int i = 0;

for ( i=0; env[i] != NULL; ++i )

printf( “%s\n”, env[i] );

return 0;

}

HOME=/c/c/bluefox/center_manifold

SHELL=/bin/csh

TERM=vt102

USERS=bluefox

.....

+++++++++++++++++++++

printf("%s%s\n%s%s\n%s%s\n,

" Name: ", getenv("NAME"),

" User: ", getenv("USER"),

" Shell: ", getenv("SHELL"),

"Home directory: ", getenv("HOME");