Read4096

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 
 6 int read4096(char* buf) {
 7     static int count = 9999;
 8     if (count >= 4096) {
 9         count -= 4096;
10         return 4096;
11     } else {
12         int tmp = count;
13         count = 0;
14         return tmp;
15     }    
16 }
17 
18 class Reader {
19     public: 
20         Reader():remain(0), size(0) {}
21         int readN(char* buf, int n) {
22             int readCount = 0;
23             while (readCount < n) {
24                 if (remain >= n - readCount) {
25                     memcpy(buf + readCount, tmp + size - remain, n - readCount);
26                     remain -= (n - readCount);
27                     readCount = n;
28                 } else {
29                     if (remain > 0) memcpy(buf, tmp + size - remain, remain);
30                     readCount += remain;
31                     remain = size = read4096(tmp);
32                     if (size == 0) break;
33                 }
34             }
35             return readCount;
36         }
37 
38         // should be more efficient, avoid some memory copy
39         int readN2(char* buf, int n) {
40             if (remain >= n) {
41                 memcpy(buf, tmp + size - remain, n);
42                 remain -= n;
43                 return n;
44             }
45             int readCount = 0;
46             if (remain > 0) {
47                 memcpy(buf, tmp + size - remain, remain);
48                 readCount += remain;
49                 remain = 0;
50             }
51             while (readCount + 4096 <= n) {
52                 int count = read4096(buf + readCount);
53                 readCount += count;
54                 if (count < 4096) {
55                     return readCount;
56                 }
57             }
58             if (readCount < n) {
59                 size = read4096(tmp);
60                 if (size >= n - readCount) {
61                     memcpy(buf + readCount, tmp, n - readCount);
62                     remain = size - n + readCount;
63                     readCount = n;
64                 } else {
65                     memcpy(buf + readCount, tmp, size);
66                     readCount += size;
67                 }
68             }
69             return readCount;
70         }
71     private:
72         int remain;
73         int size;
74         char tmp[4096];
75 };
76 int main(int argc, char** argv) {
77     freopen("input.txt", "r", stdin);
78     Reader reader;
79 
80     char buff[4096];
81     int n = 1024;
82     while (true) {
83         int count = reader.readN2(buff, n);
84         cout << n << " " << count << endl;
85         if (count == 0) break;
86     }
87 
88     return 0;
89 }