选择列范围并输出

62 行对还是64行对
 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include <string.h>
 4 #define MAX_COLS 20
 5 #define MAX_INPUT 1000
 6 
 7 int read_column_numbers( int columns[], int max );
 8 void rearrange( char *output, char const *input, 
 9     int n_columns, int const columns[] );
10 
11 int main( void )
12 {
13     int n_columns;
14     int columns[MAX_COLS];
15     char input[MAX_INPUT];
16     char output[MAX_INPUT];
17 
18     n_columns = read_column_numbers( columns, MAX_COLS );
19     while( gets(input) != NULL){
20         printf("Original input : %s\n", input);
21         rearrange( output, input, n_columns, columns );
22         printf("Rearranged line: %s\n", output);
23     }
24 
25     return EXIT_SUCCESS;
26 }
27 
28 int read_column_numbers( int columns[], int max)
29 {
30     int num = 0;
31     int ch;
32 
33     while( num < max && scanf( "%d", &columns[num]) == 1 && columns[num] >= 0)
34         num += 1;
35     if( num % 2 != 0){
36         puts( "Last column number is not paired." );
37         exit( EXIT_FAILURE );
38     }
39 
40     while ( (ch = getchar()) != EOF && ch != '\n' )
41         ;
42     
43     return num;
44 }
45 
46 void rearrange( char *output, char const *input, int n_columns, int const columns[] )
47 {
48     int col;
49     int output_col;
50     int len;
51 
52     len = strlen( input );
53     output_col = 0;
54 
55     for (col = 0; col < n_columns; col += 2)
56     {
57         int nchars = columns[col + 1] - columns[col] + 1;
58 
59         if (columns[col] >= len || output_col == MAX_INPUT - 1)
60             break;
61         if (output_col + nchars > MAX_INPUT - 1)
62             nchars = MAX_INPUT - output_col;
63             // Or this 
64             // nchars = MAX_INPUT - output_col - 1;
65             strncpy( output + output_col, input + columns[col], nchars );
66         output_col += nchars;
67     }
68     output[output_col] = '\0';
69 }