TCPL习题1-16的疑问
在TCPL P20有这样一个问题:编写一个程序,读入一组文本行,并把最长的文本行打印出来.书中已经有一程序,功能不完善.在作业1-16作者把他作为习题让读者自己解决.在习题解答中有两个程序,如下:
/* This is the first program exercise where the spec isn't entirely
* clear. The spec says, 'Revise the main routine', but the true
* length of an input line can only be determined by modifying
* getline. So that's what we'll do. getline will now return the
* actual length of the line rather than the number of characters
* read into the array passed to it.
*/
#include <stdio.h>
#define MAXLINE 1000 /* maximum input line size */
int getline(char line[], int maxline);
void copy(char to[], char from[]);
/* print longest input line */
int main(void)
{
int len; /* current line length */
int max; /* maximum length seen so far */
char line[MAXLINE]; /* current input line */
char longest[MAXLINE]; /* longest line saved here */
max = 0;
while((len = getline(line, MAXLINE)) > 0)
{
printf("%d: %s", len, line);
if(len > max)
{
max = len;
copy(longest, line);
}
}
if(max > 0)
{
printf("Longest is %d characters:\n%s", max, longest);
}
printf("\n");
return 0;
}
/* getline: read a line into s, return length */
int getline(char s[], int lim)
{
int c, i, j;
for(i = 0, j = 0; (c = getchar())!=EOF && c != '\n'; ++i)
{
if(i < lim - 1)
{
s[j++] = c;
}
}
if(c == '\n')
{
if(i <= lim - 1)
{
s[j++] = c;
}
++i;
}
s[j] = '\0';
return i;
}
/* copy: copy 'from' into 'to'; assume 'to' is big enough */
void copy(char to[], char from[])
{
int i;
i = 0;
while((to[i] = from[i]) != '\0')
{
++i;
}
}
Chris Sidi, however, was not convinced - he thought this answer was "too easy", so he checked with bwk, who agreed. Chris writes: "Looks like Mr. Kernighan meant for "main routine" in Exercise 1-16 to refer to function main(), saying your solution of modifying getline() is "too easy." :) (Though I think your solution shouldn't be removed from the Answers web site, just complimented with another one that only modifies main())"
Cue Mr "386sx", riding to the rescue on a white horse...
/* Exercise 1-16 */
#include <stdio.h>
#define MAXLINE 20
int getline(char s[], int lim);
void copy(char to[], char from[]);
int main(void)
{
char line[MAXLINE];
char longest[MAXLINE];
char temp[MAXLINE];
int len, max, prevmax, getmore;
max = prevmax = getmore = 0;
while((len = getline(line, MAXLINE)) > 0)
{
if(line[len - 1] != '\n')
{
if(getmore == 0)
copy(temp, line);
prevmax += len;
if(max < prevmax)
max = prevmax;
getmore = 1;
}
else
{
if(getmore == 1)
{
if(max < prevmax + len)
{
max = prevmax + len;
copy(longest, temp);
longest[MAXLINE - 2] = '\n';
}
getmore = 0;
}
else if(max < len)
{
max = len;
copy(longest, line);
}
prevmax = 0;
}
}
if(max > 0)
{
printf("%s", longest);
printf("len = %d\n", max);
}
return 0;
}
int getline(char s[], int lim)
{
int c, i;
for(i = 0;
i < lim - 1 && ((c = getchar()) != EOF && c != '\n');
++i)
s[i] = c;
if(c == '\n')
{
s[i] = c;
++i;
}
else if(c == EOF && i > 0)
{
/* gotta do something about no newline preceding EOF */
s[i] = '\n';
++i;
}
s[i] = '\0';
return i;
}
void copy(char to[], char from[])
{
int i;
i = 0;
while((to[i] = from[i]) != '\0')
++i;
}
对这两程序有几个问题,请教一下:
两个程序中while语句的结束条件是getline函数的返回值小于或者等于0,问题是:如果在文本的结尾那一行,没有换行,只有EOF,那么EOF在getline读最后一行时就被读过了,下一次getline做了什么呢?
另外,EOF怎么输入电脑呢?文本编辑编辑程序会自动添加吗?
问题点数：20、回复次数：2Top
1 楼cxc014（有心插柳柳不活，无心栽花花开花？）回复于 2006-03-04 17:04:08 得分 0
那么EOF在getline读最后一行时就被读过了,下一次getline做了什么呢?
===========
it calls setstate(failbit). In any case, it returns *this.(MSDN)
可以用流的fail()函数来检测.
EOF怎么输入电脑呢?文本编辑编辑程序会自动添加吗?
==========
windows console 下CTRL + Z
文本编辑编辑程序会自动添加.
Top
2 楼jixingzhong（瞌睡虫·星辰）回复于 2006-03-04 17:52:51 得分 0
EOF怎么输入电脑呢?文本编辑编辑程序会自动添加吗?
－－－－－－－－－－－－－－－－－－－－－－－
win 下 ctrl+z
unix下 ctrl+d
EOF 这个东西没有在文件中的 ....
所以也没有自动添加的说法 ....
要知道细节，
可以去看看 FILE 结构体的成员和含义，
也就是文件信息，
这里有文件的结束信息，
而不是把文件结束信息以结束符号的形式保存到文件中的 ～Top
