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获取文件总行数：
int get_line(int fd) { int line = 0,prev,ret; char ch; prev =
lseek(fd,0,SEEK_CUR); //save last seek lseek(fd,0,SEEK_SET); while(1) { ret =
read(fd, &ch,1); if(ret <= 0) { lseek(fd,prev,SEEK_SET); return line; } if(ch
== '\n') line++; } }
文件位置指针偏移到某行：
int move_line(int fd,int line) { char ch; int n = 1,ret; while(1) { if(n ==
line) return 0; ret = read(fd,&ch,1); if(ret <= 0) return -1; if(ch == '\n') {
n++; } } }
完整代码：
#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h>
#include <sys/stat.h> #include <sys/types.h> int get_line(int fd) { int line =
0,prev,ret; char ch; prev = lseek(fd,0,SEEK_CUR); //save last seek
lseek(fd,0,SEEK_SET); while(1) { ret = read(fd, &ch,1); if(ret <= 0) {
lseek(fd,prev,SEEK_SET); return line; } if(ch == '\n') line++; } } int
move_line(int fd,int line) { char ch; int n = 1,ret; while(1) { if(n == line)
return 0; ret = read(fd,&ch,1); if(ret <= 0) return -1; if(ch == '\n') { n++; }
} } int main(int argc, char **argv) { int fd_r,fd_w; int ret,size,del_line;
char ch; if(argc < 2) { fprintf(stderr,"Usage:%s <filename>\n",argv[0]);
exit(1); } fd_r = open(argv[1],O_RDONLY); if(fd_r < 0) { perror("open()");
exit(1); } fd_w = open(argv[1],O_RDWR,0666); if(fd_w < 0) { close(fd_r);
perror("open()"); exit(1); } printf("which line you wanna del:");
scanf("%d",&del_line); move_line(fd_w,del_line); move_line(fd_r,del_line + 1);
while(1) { ret = read(fd_r,&ch,1); if(ret <= 0) break; write(fd_w,&ch,1); }
if(ret < 0) { perror("read"); exit(1); } size = lseek(fd_w,0,SEEK_CUR);
ftruncate(fd_w,size); close(fd_r); close(fd_w); return 0; }