fgets读取怎么换行呢？

[debugdebugger]

程序接受两个命令行参数，第一个是一个字符，第二个是文件名
要求程序只打印文件中包含给定字符的那些行

#include <stdio.h>
#include <stdlib.h>
#define MAX 256
int has_ch(char ,const char *);
int main(int argc,char *argv[])
{
      FILE *fp;char arr[MAX],ch;
      if(argc!=3)
      {
            printf("no enough arguments:");
            exit(EXIT_FAILURE);
      }
      ch=argv[1][0];
      if((fp=fopen(argv[2],"r"))==NULL)
      {
            printf("can't open %s",argv[2]);
            exit(1);
      }
      while(fgets(arr,MAX,fp)!=NULL)
      {
            if(has_ch(ch,arr))
                  fputs(arr,stdout);
      }
      fclose(fp);
      return 0;
}
int has_ch(char ch,const char *arr)
{
      while(*arr)
            if(ch==*arr++)
            return 1;
      return 0;
}

我编译好后再命令行输入 test.exe a txt.txt
其中txt.txt内容为
adsf
dfdfde
asff
adfdfdf

我想问的是

   while(fgets(arr,MAX,fp)!=NULL)
      {
            if(has_ch(ch,arr))
                  fputs(arr,stdout);
      }

是怎么一行一行读取字符串的
当执行第2次 while(fgets(arr,MAX,fp)!=NULL)，fgets是怎么变为从txt.txt第2行开始读取的？还是其他情况

[pengzhixi]

因为遇到换行符 fgets就会停止读取。

[debugdebugger]

[Quote=引用 1 楼 pengzhixi 的回复:]

因为遇到换行符 fgets就会停止读取。
[/Quote]
所以一开始读完adsf及'\n'后，返回指针不是NULL，进入循环体，
接着往下一个字符读取直到最后读到EOF，返回NULL，退出循环是吗？

[守护神2501]

标准流是用换行符刷新缓冲区的。。。。

[pengzhixi]

char * fgets ( char * str, int num, FILE * stream );
Get string from stream

Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or a the End-of-File is reached, whichever comes first.
A newline character makes fgets stop reading, but it is considered a valid character and therefore it is included in the string copied to str.
A null character is automatically appended in str after the characters read to signal the end of the C string.

[debugdebugger]

[Quote=引用 4 楼 pengzhixi 的回复:]

char * fgets ( char * str, int num, FILE * stream );
Get string from stream

Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a……
[/Quote]
谢谢

再请问一下对我这个程序来讲“A newline character makes fgets stop reading”
是说stop reading后，进入循环体，执行完然后再继续往下读取直到EOF是吗？

[AnYidan]

[Quote=引用 5 楼 smilencetion 的回复:]
引用 4 楼 pengzhixi 的回复:

char * fgets ( char * str, int num, FILE * stream );
Get string from stream

Reads characters from stream and stores them as a C string into str until (num-1) characters ha……
[/Quote]
是的！

[Ever_lover]

说白了就是俩个条件，一是遇到换行符停止同时把换行符读取到buffer中，二是 读取一定的字节，读完就ok

[nanjingnew4]

我猜楼主想问的是他凭什么去读第二行数据，而不是继续读第一行数据，这个问题我也想过，现在在楼上找到答案了

[k841366951]

这个是因为文件类成员中有一个当前位置的指针，随着fgets的读取也自动向后移动，所以fgets每次读取的都是下一行。

[qwer_boo]

[Quote=引用 4 楼 pengzhixi 的回复:]

char * fgets ( char * str, int num, FILE * stream );
Get string from stream

Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a……
[/Quote]大牛就是大牛...

[「已注销」]

我也长见识了！谢谢了。