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select函数

分类： LINUX

2015-12-02 15:45:14

select.c文件

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  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <stdlib.h>
  4. #include <unistd.h>
  5. #include <sys/select.h>

  7. int main(int argc, char * * argv)
  8. {
  9.         fd_set fdset;
  10.         
  11.         FD_ZERO(&fdset); /*清空集合中所有元素*/
  12.         
  13.         FD_SET(STDIN_FILENO, &fdset); /*将STDIN_FILENO加入集合中*/
  14.         
  15.         int ret;
  16.         
  17.         ret = FD_ISSET(STDIN_FILENO, &fdset); /*测试STDIN_FILENO 是否包含在集合中*/
  18.         if(ret == 1)
  19.         {
  20.                 printf("STDIN_FILENO 已经被设置了！fdset=[%d]\n", fdset);
  21.         }
  22.         else if(ret == 0)
  23.         {
  24.                 printf("STDIN_FILENO 已经未被设置！\n");
  25.         }
  26.         
  27.         FD_CLR(STDIN_FILENO, &fdset); /*将STDIN_FILENO 从集合中清除*/
  28.         ret = FD_ISSET(STDIN_FILENO, &fdset);
  29.         if(ret == 1)
  30.         {
  31.                 printf("STDIN_FILENO 已经被设置了！fdset=[%d]\n", fdset);
  32.         }
  33.         else if(ret == 0)
  34.         {
  35.                 printf("STDIN_FILENO 已经未被设置！\n");
  36.         }
  37.         
  38.         return 0;    
  39. }
select2.c文件

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  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <stdlib.h>
  4. #include <unistd.h>
  5. #include <fcntl.h>
  6. #include <sys/select.h>
  7. #include <assert.h>

  9. int isReadReady(int fd);
  10. int isWriteReady(int fd);

  12. int main(int argc, char * * argv)
  13. {
  14.         int ret = -1;
  15.         int fd = STDOUT_FILENO;
  16.         ret = isReadReady(fd);
  17.         if(ret == 1)
  18.         {
  19.                 printf("fd=[%d] 可读!\n", fd);
  20.         }
  21.         else if(ret == 0)
  22.         {
  23.                 printf("fd=[%d] 不可读!\n", fd);
  24.         }
  25.         
  26.         ret = isWriteReady(fd);
  27.         if(ret == 1)
  28.         {
  29.                 printf("fd=[%d] 可读!\n", fd);
  30.         }
  31.         else if(ret == 0)
  32.         {
  33.                 printf("fd=[%d] 不可读!\n", fd);
  34.         }
  35.         
  36.         fd = STDIN_FILENO;
  37.         ret = isReadReady(fd);
  38.         if(ret == 1)
  39.         {
  40.                 printf("fd=[%d] 可读!\n", fd);
  41.         }
  42.         else if(ret == 0)
  43.         {
  44.                 printf("fd=[%d] 不可读!\n", fd);
  45.         }
  46.         
  47.         ret = isWriteReady(fd);
  48.         if(ret == 1)
  49.         {
  50.                 printf("fd=[%d] 可读!\n", fd);
  51.         }
  52.         else if(ret == 0)
  53.         {
  54.                 printf("fd=[%d] 不可读!\n", fd);
  55.         }
  56.         
  57.         printf("**************************************\n");
  58.         int keyboard;
  59.         char ch;
  60.         fd_set readfd;
  61.         struct timeval timeout;
  62.         
  63.         //keyboard = open("/dev/tty", O_RDONLY|O_NONBLOCK); /*/dev/tty就是控制终端*/
  64.         keyboard = 0;
  65.         printf("keyboard=[%d]\n", keyboard);
  66.         //assert(keyboard > 0);
  67.         
  68.         read(keyboard, &ch, 1*sizeof(char));
  69.         printf("输入字符=[%c]\n", ch);

  71.         while(1)
  72.         {
  73.                 timeout.tv_sec = 1;
  74.                 timeout.tv_usec = 0;
  75.                 FD_ZERO(&readfd);
  76.                 FD_SET(keyboard, &readfd);
  77.                 
  78.                 /*标准输入文件中，即屏幕中，
  79.                 如果没有数据，则表示读状态还未准备好：直接去read会阻塞。
  80.                 如果有数据，则表示读状态已经准备好：直接去read，不会阻塞，
  81.                 所以select函数执行时：
  82.                 若标准输入文件中有数据，read不会阻塞，则此描述符是准备好啊，则select立马检测到，select不会阻塞，立即返回1。
  83.                 若标准输入文件中没有数据，read会阻塞，未准备好，则select会阻塞1秒，1秒内还没有数据的话，还未准备好，再返回0*/
  84.                 ret = select(keyboard+10, &readfd, NULL, NULL, &timeout);
  85.                 printf("select ret=[%d]\n", ret);
  86.                 if(ret < 0)
  87.                 {
  88.                         printf("select err!\n");
  89.                         return -1;
  90.                 }
  91.                 
  92.                 ret = FD_ISSET(keyboard, &readfd);
  93.                 printf("FD_ISSET ret=[%d]\n", ret);
  94.                 if(ret == 1) /*可读*/
  95.                 {
  96.                         printf("===========\n");
  97.                         read(keyboard, &ch, 1*sizeof(char));
  98.                         if(ch == '\n')
  99.                         {
  100.                                 continue;
  101.                         }
  102.                         printf("输入字符=[%c]\n", ch);
  103.                         
  104.                         if(ch == 'q')
  105.                         {
  106.                                 break;
  107.                         }
  108.                 }
  109.         }
  110.         
  111.         return 0;
  112. }

  114. /*功能：测试文件fd是否可读*/
  115. int isReadReady(int fd)
  116. {
  117.         int ret = -1;
  118.         fd_set readfdset;
  119.         struct timeval time;
  120.         memset(&time, 0, sizeof(struct timeval));
  121.         
  122.         FD_ZERO(&readfdset);
  123.         FD_SET(fd, &readfdset);
  124.         time.tv_sec = 0;
  125.         time.tv_usec = 0;
  126.         
  127.         ret = select(fd+1, &readfdset, NULL, NULL, &time);
  128.         printf("select ret=[%d]\n", ret);
  129.         if(ret < 0)
  130.         {
  131.                 printf("select err!\n");
  132.                 return -1;
  133.         }
  134.         ret = FD_ISSET(fd, &readfdset);
  135.         if(ret == 1)
  136.         {
  137.                 return 1;
  138.         }
  139.         else if(ret == 0)
  140.         {
  141.                 return 0;
  142.         }
  143. }

  145. /*功能：测试文件fd是否可写*/
  146. int isWriteReady(int fd)
  147. {
  148.         int ret = -1;
  149.         fd_set writefdset;
  150.         struct timeval time;
  151.         memset(&time, 0, sizeof(struct timeval));
  152.         
  153.         FD_ZERO(&writefdset);
  154.         FD_SET(fd, &writefdset);
  155.         time.tv_sec = 0;
  156.         time.tv_usec = 0;
  157.         
  158.         ret = select(fd+1, NULL, &writefdset, NULL, &time);
  159.         printf("select ret=[%d]\n", ret);
  160.         if(ret < 0)
  161.         {
  162.                 printf("select err!\n");
  163.                 return -1;
  164.         }
  165.         ret = FD_ISSET(fd, &writefdset);
  166.         if(ret == 1)
  167.         {
  168.                 return 1;
  169.         }
  170.         else if(ret == 0)
  171.         {
  172.                 return 0;
  173.         }
  174. }
select3.c文件

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  1. #include <stdio.h>
  2. #include <string.h>
  3. #include <stdlib.h>
  4. #include <unistd.h>
  5. #include <fcntl.h>
  6. #include <sys/select.h>
  7. #include <assert.h>

  9. int isReadReady(int fd);
  10. int isWriteReady(int fd);

  12. int main(int argc, char * * argv)
  13. {
  14.         int ret = -1;
  15.         int fd = STDOUT_FILENO;
  16.         ret = isReadReady(fd);
  17.         if(ret == 1)
  18.         {
  19.                 printf("fd=[%d] 可读!\n", fd);
  20.         }
  21.         else if(ret == 0)
  22.         {
  23.                 printf("fd=[%d] 不可读!\n", fd);
  24.         }
  25.         
  26.         ret = isWriteReady(fd);
  27.         if(ret == 1)
  28.         {
  29.                 printf("fd=[%d] 可读!\n", fd);
  30.         }
  31.         else if(ret == 0)
  32.         {
  33.                 printf("fd=[%d] 不可读!\n", fd);
  34.         }
  35.         
  36.         fd = STDIN_FILENO;
  37.         ret = isReadReady(fd);
  38.         if(ret == 1)
  39.         {
  40.                 printf("fd=[%d] 可读!\n", fd);
  41.         }
  42.         else if(ret == 0)
  43.         {
  44.                 printf("fd=[%d] 不可读!\n", fd);
  45.         }
  46.         
  47.         ret = isWriteReady(fd);
  48.         if(ret == 1)
  49.         {
  50.                 printf("fd=[%d] 可读!\n", fd);
  51.         }
  52.         else if(ret == 0)
  53.         {
  54.                 printf("fd=[%d] 不可读!\n", fd);
  55.         }
  56.         
  57.         printf("**************************************\n");
  58.         int keyboard;
  59.         char ch;
  60.         char str[128];
  61.         fd_set writefd;
  62.         struct timeval timeout;
  63.         
  64.         //keyboard = open("/dev/tty", O_RDONLY|O_NONBLOCK); /*/dev/tty就是控制终端*/
  65.         keyboard = STDOUT_FILENO;
  66.         printf("keyboard=[%d]\n", keyboard);
  67.         //assert(keyboard > 0);
  68.         
  69.         strcpy(str, "wangxiancai");
  70.         printf("输出字符=\n");
  71.         write(keyboard, str, strlen(str));
  72.         printf("\n");
  73.         
  74.         while(1)
  75.         {
  76.                 sleep(1);
  77.                 timeout.tv_sec = 1;
  78.                 timeout.tv_usec = 0;
  79.                 FD_ZERO(&writefd);
  80.                 FD_SET(keyboard, &writefd);
  81.                 
  82.                 /*标准输出文件：任何时候都是可写的，即任何时候都是准备好的。
  83.                 所以在select一执行，就能立马检测到有描述符准备好，select根本不会有阻塞现象。*/
  84.                 ret = select(keyboard+10, NULL, &writefd, NULL, &timeout);
  85.                 printf("select ret=[%d]\n", ret);
  86.                 if(ret < 0)
  87.                 {
  88.                         printf("select err!\n");
  89.                         return -1;
  90.                 }
  91.                 
  92.                 ret = FD_ISSET(keyboard, &writefd);
  93.                 printf("FD_ISSET ret=[%d]\n", ret);
  94.                 if(ret == 1) /*可写*/
  95.                 {
  96.                         printf("===========\n");
  97.                         printf("输出字符=\n");
  98.                         memset(str, 0, sizeof(str));
  99.                         strcpy(str, "wangxiancai");
  100.                         write(keyboard, str, strlen(str));
  101.                         printf("\n");
  102.                 }
  103.         }
  104.         
  105.         return 0;
  106. }

  108. /*功能：测试文件fd是否可读*/
  109. int isReadReady(int fd)
  110. {
  111.         int ret = -1;
  112.         fd_set readfdset;
  113.         struct timeval time;
  114.         memset(&time, 0, sizeof(struct timeval));
  115.         
  116.         FD_ZERO(&readfdset);
  117.         FD_SET(fd, &readfdset);
  118.         time.tv_sec = 0;
  119.         time.tv_usec = 0;
  120.         
  121.         ret = select(fd+1, &readfdset, NULL, NULL, &time);
  122.         printf("select ret=[%d]\n", ret);
  123.         if(ret < 0)
  124.         {
  125.                 printf("select err!\n");
  126.                 return -1;
  127.         }
  128.         ret = FD_ISSET(fd, &readfdset);
  129.         if(ret == 1)
  130.         {
  131.                 return 1;
  132.         }
  133.         else if(ret == 0)
  134.         {
  135.                 return 0;
  136.         }
  137. }

  139. /*功能：测试文件fd是否可写*/
  140. int isWriteReady(int fd)
  141. {
  142.         int ret = -1;
  143.         fd_set writefdset;
  144.         struct timeval time;
  145.         memset(&time, 0, sizeof(struct timeval));
  146.         
  147.         FD_ZERO(&writefdset);
  148.         FD_SET(fd, &writefdset);
  149.         time.tv_sec = 0;
  150.         time.tv_usec = 0;
  151.         
  152.         ret = select(fd+1, NULL, &writefdset, NULL, &time);
  153.         printf("select ret=[%d]\n", ret);
  154.         if(ret < 0)
  155.         {
  156.                 printf("select err!\n");
  157.                 return -1;
  158.         }
  159.         ret = FD_ISSET(fd, &writefdset);
  160.         if(ret == 1)
  161.         {
  162.                 return 1;
  163.         }
  164.         else if(ret == 0)
  165.         {
  166.                 return 0;
  167.         }
  168. }



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