Base64是常见的加密算法，代码实现了基于C++的对于base64的编码和解码。
其中注释掉的部分为编码部分，取消注释将解码部分注释掉即可实现编码，反之可以实现解码。
1 #include <stdio.h>
2 #include <string.h>
3 #include <assert.h>
4
5 typedef unsigned char uint8;
6 typedef unsigned long uint32;
7
8 static uint8 alphabet_map[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
9 static uint8 reverse_map[] =
10 {
11 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
12 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
13 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 62, 255, 255, 255, 63,
14 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255, 255, 255, 255, 255,
15 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
16 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255, 255, 255,
17 255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
18 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 255, 255, 255, 255, 255
19 };
20
21 uint32 base64_encode(const uint8 *text, uint32 text_len, uint8 *encode)
22 {
23 uint32 i, j;
24 for (i = 0, j = 0; i+3 <= text_len; i+=3)
25 {
26 encode[j++] = alphabet_map[text[i]>>2]; //取出第一个字符的前6位并找出对应的结果字符
27 encode[j++] = alphabet_map[((text[i]<<4)&0x30)|(text[i+1]>>4)]; //将第一个字符的后2位与第二个字符的前4位进行组合并找到对应的结果字符
28 encode[j++] = alphabet_map[((text[i+1]<<2)&0x3c)|(text[i+2]>>6)]; //将第二个字符的后4位与第三个字符的前2位组合并找出对应的结果字符
29 encode[j++] = alphabet_map[text[i+2]&0x3f]; //取出第三个字符的后6位并找出结果字符
30 }
31
32 if (i < text_len)
33 {
34 uint32 tail = text_len - i;
35 if (tail == 1)
36 {
37 encode[j++] = alphabet_map[text[i]>>2];
38 encode[j++] = alphabet_map[(text[i]<<4)&0x30];
39 encode[j++] = '=';
40 encode[j++] = '=';
41 }
42 else //tail==2
43 {
44 encode[j++] = alphabet_map[text[i]>>2];
45 encode[j++] = alphabet_map[((text[i]<<4)&0x30)|(text[i+1]>>4)];
46 encode[j++] = alphabet_map[(text[i+1]<<2)&0x3c];
47 encode[j++] = '=';
48 }
49 }
50 return j;
51 }
52
53 uint32 base64_decode(const uint8 *code, uint32 code_len, uint8 *plain)
54 {
55 assert((code_len&0x03) == 0); //如果它的条件返回错误，则终止程序执行。4的倍数。
56
57 uint32 i, j = 0;
58 uint8 quad[4];
59 for (i = 0; i < code_len; i+=4)
60 {
61 for (uint32 k = 0; k < 4; k++)
62 {
63 quad[k] = reverse_map[code[i+k]];//分组，每组四个分别依次转换为base64表内的十进制数
64 }
65
66 assert(quad[0]<64 && quad[1]<64);
67
68 plain[j++] = (quad[0]<<2)|(quad[1]>>4); //取出第一个字符对应base64表的十进制数的前6位与第二个字符对应base64表的十进制数的前2位进行组合
69
70 if (quad[2] >= 64)
71 break;
72 else if (quad[3] >= 64)
73 {
74 plain[j++] = (quad[1]<<4)|(quad[2]>>2); //取出第二个字符对应base64表的十进制数的后4位与第三个字符对应base64表的十进制数的前4位进行组合
75 break;
76 }
77 else
78 {
79 plain[j++] = (quad[1]<<4)|(quad[2]>>2);
80 plain[j++] = (quad[2]<<6)|quad[3];//取出第三个字符对应base64表的十进制数的后2位与第4个字符进行组合
81 }
82 }
83 return j;
84 }
85
86
87 /*int main(void)
88 {
89 char input[256];
90 while (true){
91 printf("Please input string: ");
92 scanf("%s", input);
93 uint8 *text = (uint8 *)input;
94 uint32 text_len = (uint32)strlen((char *)text);
95 uint8 buffer[1024], buffer2[4096];
96 uint32 size = base64_encode(text, text_len, buffer2);
97 buffer2[size] = 0;
98 printf("%s\n", buffer2);
99
100 size = base64_decode(buffer2, size, buffer);
101 buffer[size] = 0;
102 printf("%s\n", buffer);
103
104 }
105 return 0;
106 }*/
107 //编码
108 int main(void)
109 {
110 char input[256];
111 while (true){
112 printf("Please input what you want to decode: ");
113 scanf("%s", input);
114 uint8 *text = (uint8 *)input;
115 uint32 text_len = (uint32)strlen((char *)text);
116 uint8 buffer[1024],buffer2[4096];
117
118 uint32 size = base64_decode(text, text_len, buffer);
119 buffer[size] = 0;
120 printf("Decoded content: %s\n", buffer);
121 size = base64_encode(buffer, size, buffer2);
122 buffer2[size] = 0;
123 printf("Confirmation of the original content: %s\n", buffer2);
124 }
125 return 0;
126 }
127 //解码