c_水程序

  1 *
  2 ** This program reads input lines from the standard input and prints
  3 ** each input line, followed by just some portions of the lines, to
  4 ** the standard output.
  5 ** 
  6 ** The first input is a list of column numbers, which ends with a
  7 ** negative number.  The column numbers are paired and specify
  8 ** ranges of columns from the input line that are to be printed.
  9 ** For example, 0 3 10 12 -1 indicates that only columns 0 through 3
 10 ** and columns 10 through 12 will be printed.
 11 */
 12 
 13 #include <stdio.h>
 14 #include <stdlib.h>
 15 #include <string.h>
 16 #define    MAX_COLS    20    /* max # of columns to process */
 17 #define    MAX_INPUT    1000    /* max len of input & output lines */
 18 
 19 int    read_column_numbers( int columns[], int max );
 20 void    rearrange( char *output, char const *input,
 21         int n_columns, int const columns[] );
 22 
 23 int
 24 main( void )
 25 {
 26     int    n_columns;        /* # of columns to process */
 27     int    columns[MAX_COLS];    /* the columns to process */
 28     char    input[MAX_INPUT];    /* array for input line */
 29     char    output[MAX_INPUT];    /* array for output line */
 30 
 31     /*
 32     ** Read the list of column numbers
 33     */
 34     n_columns = read_column_numbers( columns, MAX_COLS );
 35 
 36     /*
 37     ** Read, process and print the remaining lines of input.
 38     */
 39     while( gets( input ) != NULL ){
 40         printf( "Original input : %s\n", input );
 41         rearrange( output, input, n_columns, columns );
 42         printf( "Rearranged line: %s\n", output );
 43     }
 44 
 45     return EXIT_SUCCESS;
 46 }
 47 
 48 *
 49 ** Read the list of column numbers, ignoring any beyond the specified
 50 ** maximum.
 51 */
 52 int
 53 read_column_numbers( int columns[], int max )
 54 {
 55     int    num = 0;
 56     int    ch;
 57 
 58     /*
 59     ** Get the numbers, stopping at eof or when a number is < 0.
 60     */
 61     while( num < max && scanf( "%d", &columns[num] ) == 1
 62         && columns[num] >= 0 )
 63         num += 1;
 64 
 65     /*
 66     ** Make sure we have an even number of inputs, as they are
 67     ** supposed to be paired.
 68     */
 69     if( num % 2 != 0 ){
 70         puts( "Last column number is not paired." );
 71         exit( EXIT_FAILURE );
 72     }
 73 
 74     /*
 75     ** Discard the rest of the line that contained the final
 76     ** number.
 77     */
 78     while( (ch = getchar()) != EOF && ch != '\n' )
 79         ;
 80 
 81     return num;
 82 }
 83 
 84 *
 85 ** Process a line of input by concatenating the characters from
 86 ** the indicated columns.  The output line is then NUL terminated.
 87 */
 88 void
 89 rearrange( char *output, char const *input,
 90     int n_columns, int const columns[] )
 91 {
 92     int    col;        /* subscript for columns array */
 93     int    output_col;    /* output column counter */
 94     int    len;        /* length of input line */
 95 
 96     len = strlen( input );
 97     output_col = 0;
 98 
 99     /*
100     ** Process each pair of column numbers.
101     */
102     for( col = 0; col < n_columns; col += 2 ){
103         int    nchars = columns[col + 1] - columns[col] + 1;
104 
105         /*
106         ** If the input line isn't this long or the output
107         ** array is full, we're done.
108         */
109         if( columns[col] >= len ||
110             output_col == MAX_INPUT - 1 )
111             break;
112 
113         /*
114         ** If there isn't room in the output array, only copy
115         ** what will fit.
116         */
117         if( output_col + nchars > MAX_INPUT - 1 )
118             nchars = MAX_INPUT - output_col - 1;
119 
120         /*
121         ** Copy the relevant data.
122         */
123         strncpy( output + output_col, input + columns[col],
124             nchars );
125         output_col += nchars;
126     }
127 
128     output[output_col] = '\0';
129 }