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  • linux系统编程：read,write与lseek的综合应用

    这个实例根据命令行参数进行相应的读学操作：

    用法：

    usage:./io file {r<length>|R<length>|w<string>|s<offset>}...

    file参数：文件名， 如果不存在会自动创建

    r<length>：  如r5,   r: 读取操作，表示在当前文件指针后面读取5个字节的内容，以文本形式输出.

    R<length>：如R5   R:读取操作，表示在当前文件指针后面读取5个字节的内容，以十六进制形式输出.

    w<string>： 如wghostwu:  w表示写入操作，表示在当前文件指针后面写入5个字节的内容

    s<offset>: 如s1000, 从文件开头把指针移动1000个字节

    源代码：

      1 /*================================================================
  2 *   Copyright (C) 2018 . All rights reserved.
  3 *   
  4 *   文件名称：io.c
  5 *   创 建 者：ghostwu(吴华)
  6 *   创建日期：2018年01月10日
  7 *   描    述：write,open,lseek结合示例
  8 *
  9 ================================================================*/
 10 
 11 #include <stdio.h>
 12 #include <stdlib.h>
 13 #include <string.h>
 14 #include <sys/types.h>
 15 #include <sys/stat.h>
 16 #include <fcntl.h>
 17 #include <limits.h>
 18 #include <sys/types.h>
 19 #include <unistd.h>
 20 
 21 //参数字符串转整数
 22 int str_to_long( char* str );
 23 
 24 int main(int argc, char *argv[])
 25 {
 26     int i = 2;
 27     int fd = -1;
 28     //保存字符串转整形的结果
 29     int res;
 30     //写入的字节数
 31     ssize_t num;
 32     //动态分配的堆内存
 33     char* buf;
 34     //读取的字节数
 35     int numread;
 36 
 37     if( argc < 3 || strcmp( argv[1], "--help" ) == 0 )  {
 38         printf( "usage:%s file {r<length>|R<length>|w<string>|s<offset>}...
", argv[0] );
 39         exit( -1 );
 40     }
 41 
 42     fd = open( argv[1], O_RDWR | O_CREAT, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH );
 43     if( fd < 0 ) {
 44         printf( "文件%s打开或者创建失败", argv[1] );
 45         exit( -1 );
 46     }
 47     
 48     for( i = 2; i < argc; i++ ){
 49         switch( argv[i][0] ){ 
 50             //移动指针, s后面跟移动的字节数
 51             case 's':
 52                 res = str_to_long( &argv[i][1] );
 53                 if( -1 == res ) {
 54                     printf( "字符串->整形转换失败
" );
 55                     exit( -1 );
 56                 }
 57                 lseek( fd, res, SEEK_CUR );    
 58                 printf( "%s--->指针移动成功
", argv[i] );
 59                 break;
 60             //写入文件, w后面跟写入的内容
 61             case 'w':
 62                 num = write( fd, &argv[i][1], strlen( &argv[i][1] ) );
 63                 if( num == -1 ) {
 64                     printf( "%s写入失败
", argv[i] );
 65                 }
 66                 printf( "%s成功写入%ld个字节
", argv[i], num );
 67                 break;
 68             case 'r': //字符输出
 69             case 'R': //十六进制输出
 70                 res = str_to_long( &argv[i][1] );
 71                 if( -1 == res ) {
 72                     printf( "字符串->整形转换失败
" );
 73                     exit( -1 );
 74                 }
 75                 buf = malloc( res );
 76                 if( buf == NULL ){
 77                     printf( "内存分配失败" );
 78                     exit( -1 );
 79                 }
 80                 numread = read( fd, buf, res );
 81                 if( -1 == numread ) {
 82                     printf( "数据读取失败
" );
 83                     exit( -1 );
 84                 }
 85                 if( 0 == numread ) {
 86                     printf( "已经到达文件尾部" );
 87                 }else {
 88                     printf( "%s: ", argv[i] );
 89                     for ( int j = 0 ; j < numread; j ++ ){
 90                         if( 'r' == argv[i][0] ) {
 91                             printf( "%c", buf[j] );
 92                         }else {
 93                             printf( "%02x ", buf[j] );
 94                         }
 95                     }
 96                 }
 97                 break;
 98             default:
 99                 printf( "参数%s必须以[rRws]中的一个开头
", argv[i] );
100         }
101     }
102 
103     return 0;
104 }
105 
106 int str_to_long( char* str ) {
107     char* endstr;
108     int res;
109     res = strtol( str, &endstr, 10 );
110     if( (res == LONG_MIN) || (res == LONG_MAX) ) {
111         return -1;
112     }
113     return res;
114 }
    View Code

    完整的演示效果：

     1 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ls
 2 cp  cp.c  cp.c.copy  io  io.c  strtol  strtol.c
 3 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ !g
 4 gcc io.c -o io
 5 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ls -l
 6 total 56
 7 -rwxrwxr-x 1 ghostwu ghostwu  9016 1月  10 17:16 cp
 8 -rw-rw-r-- 1 ghostwu ghostwu  1752 1月  10 17:15 cp.c
 9 -rw-rw-r-- 1 ghostwu ghostwu  1752 1月  10 17:16 cp.c.copy
10 -rwxrwxr-x 1 ghostwu ghostwu 13360 1月  10 22:19 io
11 -rw-rw-r-- 1 ghostwu ghostwu  2743 1月  10 22:19 io.c
12 -rwxrwxr-x 1 ghostwu ghostwu  8824 1月  10 20:47 strtol
13 -rw-rw-r-- 1 ghostwu ghostwu   616 1月  10 20:47 strtol.c
14 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ./io test.txt
15 usage:./io file {r<length>|R<length>|w<string>|s<offset>}...
16 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ls -l
17 total 56
18 -rwxrwxr-x 1 ghostwu ghostwu  9016 1月  10 17:16 cp
19 -rw-rw-r-- 1 ghostwu ghostwu  1752 1月  10 17:15 cp.c
20 -rw-rw-r-- 1 ghostwu ghostwu  1752 1月  10 17:16 cp.c.copy
21 -rwxrwxr-x 1 ghostwu ghostwu 13360 1月  10 22:19 io
22 -rw-rw-r-- 1 ghostwu ghostwu  2743 1月  10 22:19 io.c
23 -rwxrwxr-x 1 ghostwu ghostwu  8824 1月  10 20:47 strtol
24 -rw-rw-r-- 1 ghostwu ghostwu   616 1月  10 20:47 strtol.c
25 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ./io test.txt s1000 wghostwu
26 s1000--->指针移动成功
27 wghostwu成功写入7个字节
28 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ls -l
29 total 60
30 -rwxrwxr-x 1 ghostwu ghostwu  9016 1月  10 17:16 cp
31 -rw-rw-r-- 1 ghostwu ghostwu  1752 1月  10 17:15 cp.c
32 -rw-rw-r-- 1 ghostwu ghostwu  1752 1月  10 17:16 cp.c.copy
33 -rwxrwxr-x 1 ghostwu ghostwu 13360 1月  10 22:19 io
34 -rw-rw-r-- 1 ghostwu ghostwu  2743 1月  10 22:19 io.c
35 -rwxrwxr-x 1 ghostwu ghostwu  8824 1月  10 20:47 strtol
36 -rw-rw-r-- 1 ghostwu ghostwu   616 1月  10 20:47 strtol.c
37 -rw-rw-r-- 1 ghostwu ghostwu  1007 1月  10 22:20 test.txt
38 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ./io test.txt r1007
39 r1007: ghostwughostwu@ubuntu:~/c_program/tlpi/chapter4$ ./io test.txt R1007
40 R1007: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 67 68 6f 73 74 77 75 
    41 ghostwu@ubuntu:~/c_program/tlpi/chapter4$ ./io test.txt s1000 r7
42 s1000--->指针移动成功
43 r7: ghostwughostwu@ubuntu:~/c_program/tlpi/chapter4$ ./io test.txt s1000 R7
44 s1000--->指针移动成功
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  • 原文地址：https://www.cnblogs.com/ghostwu/p/8261151.html
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