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Input / Output and the OS

Input / Output and the OS. Declarations and Initializations. char c = ‘A’, s[] = “Blue moon!”;. Declarations and Initializations. int i = 123; double x = 0.123456789;. Input and Output functions. fprintf(), fscanf(), sprintf(), sscanf()

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Input / Output and the OS

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  1. Input / Output and the OS

  2. Declarations and Initializations • char c = ‘A’, s[] = “Blue moon!”;

  3. Declarations and Initializations • int i = 123; • double x = 0.123456789;

  4. Input and Output functions • fprintf(), 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 to

  5. sprintf and sscanf • int sprintf(char *s , const char *format, ...); • int sscanf(const char *s, const char *format, ...);

  6. 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 print into the string print the string to the screen

  7. 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 pointers open the files for reading / writing close the files

  8. 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 ) • { the return value make sure that we got all the input parameters

  9. 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 open make sure the output file is open mark the error type (which file did not open ... )

  10. Double Spacing a File the else of ( argc == 3 ) • else • { • rtVal = 1; • prn_info( argv[0] ); • } • if ( rtVal > 1 ) • prn_err_msg( argv[ 2 ] ); • return rtVal; • } file not open error message

  11. 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 ); • }

  12. 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 it

  13. 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); • }

  14. Replicating a File with Caps • 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; • }

  15. 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

  16. 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

  17. fseek • fseek(file_ptr, offset, place); • #define SEEK_SET 0 • #define SEEK_CUR 1 • #define SEEK_END 2 • ftell(file_ptr); beginning of the file current position in the file end of the file

  18. 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-dos

  19. Write a File Backwards move to the end of the file • 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; • } back up one character move ahead one character back up two characters

  20. 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-dos open file file permissions

  21. 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 file

  22. File Permissions • r-- 100 04 • -w- 010 02 • --x 001 01 • rw- 110 06 • r-x 101 05 • -wx 011 03 • rwx 111 07 • ++++++ • rw------- 0600 • rw----r-- 0604 • rwxr-xr-x 0755 • rwxrwxrwx 0777

  23. 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

  24. 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 performed

  25. 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 reading open the file for writing

  26. 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 file write to the file close the files

  27. 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 name

  28. 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 command remove the temporary file

  29. #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; • }

  30. 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 function create a number between 0 and 9999

  31. 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; • }

  32. Profiling • cc -p -o quicksort main.c quicksort.c • quicksort→mon.out • prof quicksort

  33. 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 machine machine dependent seconds since 1970

  34. 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 file

  35. 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);

  36. Timing Functions print the values found, and do it neatly • 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; • }

  37. 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 million arbitrary values

  38. 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; • }

  39. 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

  40. #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; • }

  41. 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");

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