将输入的空格串替换为最少数量的制表符和空格。

#include <stdio.h>

#define MAXLINE 1000 /* max input line size */
#define TAB2SPACE 4 /* 4 spaces to a tab */

char line[MAXLINE]; /*current input line*/

int getline(void);  /* taken from the KnR book. */

int
main()
{
int i, t;
int spacecount, len;

while ((len = getline()) > 0)
{
spacecount = 0;
for (i = 0; i < len; i++)
{
if (line[i] == ' ')
spacecount++; /* increment counter for each space */
if (line[i] != ' ')
spacecount = 0; /* reset counter */
if (spacecount == TAB2SPACE) /* Now we have enough spaces
** to replace them with a tab
*/
{
/* Because we are removing 4 spaces and
** replacing them with 1 tab we move back
** three chars and replace the ' ' with a \t
*/
i -= 3; /* same as "i = i - 3" */
len -= 3;
line[i] = '\t';
/* Now move all the char's to the right into the
** places we have removed.
*/
for (t = i + 1; t<len; t++)
line[t] = line[t + 3];
/* Now set the counter back to zero and move the
** end of line back 3 spaces
*/
spacecount = 0;
line[len] = '\0';
}
}
printf("%s", line);
}
return 0;
}

/* getline: specialized version */
int getline(void)
{
int c, i;
extern char line[];

for (i = 0; i<MAXLINE - 1 && (c = getchar()) != EOF && c != '\n'; ++i)
line[i] = c;
if (c == '\n')
{
line[i] = c;
++i;
}
line[i] = '\0';
return i;

}