Linux網絡編程：read和write函數的包裝

1. #include <unistd.h>
2. #include <errno.h>
4. ssize_t readn(int fd, void *buf, size_t count)
5. {
6. char *strtmp;
7. ssize_t reval, realcount = 0;
8. strtmp = (char *)buf;
10. while (count > 0)
11. {
12. reval = read(fd, strtmp, count);
13. if (reval < 0)
14. if (errno == EINTR)
15. continue;
16. else
17. return -1;
18. else if (reval > 0)
19. {
20. count -= reval;
21. strtmp += reval;
22. realcount += reval;
23. continue;
24. }
25. else
26. break;
27. }
29. return realcount;
30. }
32. ssize_t writen(int fd, const void *buf, size_t count)
33. {
34. char *strtmp;
35. ssize_t reval, realcount = count;
36. strtmp = (char *)buf;
38. while (count > 0)
39. {
40. reval = write(fd, strtmp, count);
41. if (reval < 0)
42. if (errno == EINTR)
43. continue;
44. else
45. return -1;
47. count -= reval;
48. strtmp += reval;
49. }
51. return realcount;
52. }
54. ssize_t readline(int fd, void *buf, int size)
55. {
56. char *strtmp;
57. ssize_t reval, realcount = 0;
58. strtmp = (char *)buf;
60. while (size > 1)
61. {
62. reval = read(fd, strtmp, 1);
63. if (reval < 0)
64. if (errno == EINTR)
65. continue;
66. else
67. return -1;
68. else if (reval == 0)
69. break;
70. else
71. {
72. realcount++;
73. size--;
74. if (*strtmp++ == '\n')
75. break;
76. }
77. }
78. *strtmp = '\0';
79. return realcount;
80. }

需要注意：readline函數是每次調用一次系統函數讀取一個字節，這樣導致效率很低。