- /*
- Base64是一种基于64个可打印字符来表示二进制数据的表示方法。三个字节有24个比特,对应于4个Base64单元,即3个字节需要用4个可打印字符来表示。
- 当最后剩余一个八位字节(一个byte)时,最后一个6位的base64字节块有四位是0值,最后附加上两个等号;
- 如果最后剩余两个八位字节(2个byte)时,最后一个6位的base字节块有两位是0值,最后附加一个等号。
- */
- #include <stdio.h>
- #include "string.h"
- #include "stdlib.h"
- const char base[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
- static char find_pos(char ch);
- char *base64_encode(const char* data, int data_len,int *len);
- char *base64_decode(const char* data, int data_len,int *len);
- /**
- *找到ch在base中的位置
- */
- static char find_pos(char ch)
- {
- //the last position (the only) in base[]
- char *ptr = (char*)strrchr(base, ch);
- return (ptr - base);
- }
- /**
- *BASE64编码
- */
- char *base64_encode(const char* data, int data_len,int *len)
- {
- int prepare = 0;
- int ret_len;
- *len=0;
- int temp = 0;
- char *ret = NULL;
- char *f = NULL;
- int tmp = 0;
- char changed[4];
- int i = 0;
- ret_len = data_len / 3;
- temp = data_len % 3;
- if (temp > 0)
- {
- ret_len += 1;
- }
- //最后一位以''结束
- ret_len = ret_len*4 + 1;
- ret = (char *)malloc(ret_len);
- if ( ret == NULL)
- {
- printf("No enough memory.n");
- exit(0);
- }
- memset(ret, 0, ret_len);
- f = ret;
- //tmp记录data中移动位置
- while (tmp < data_len)
- {
- temp = 0;
- prepare = 0;
- memset(changed, 0, 4);
- while (temp < 3)
- {
- if (tmp >= data_len)
- {
- break;
- }
- //将data前8*3位移入prepare的低24位
- prepare = ((prepare << 8) | (data[tmp] & 0xFF));
- tmp++;
- temp++;
- }
- //将有效数据移到以prepare的第24位起始位置
- prepare = (prepare<<((3-temp)*8));
- for (i = 0; i < 4 ;i++ )
- {
- //最后一位或两位
- if (temp < i)
- {
- changed[i] = 0x40;
- }
- else
- {
- //24位数据
- changed[i] = (prepare>>((3-i)*6)) & 0x3F;
- }
- *f = base[changed[i]];
- f++;
- (*len)++;
- }
- }
- *f = '';
- return ret;
- }
- /**
- *BASE64解码
- */
- char *base64_decode(const char *data, int data_len,int *len)
- {
- int ret_len = (data_len / 4) * 3+1;
- int equal_count = 0;
- char *ret = NULL;
- char *f = NULL;
- *len=0;
- int tmp = 0;
- int temp = 0;
- char need[3];
- int prepare = 0;
- int i = 0;
- if (*(data + data_len - 1) == '=')
- {
- equal_count += 1;
- }
- if (*(data + data_len - 2) == '=')
- {
- equal_count += 1;
- }
- ret = (char *)malloc(ret_len);
- if (ret == NULL)
- {
- printf("No enough memory.n");
- exit(0);
- }
- memset(ret, 0, ret_len);
- f = ret;
- while (tmp < (data_len - equal_count))
- {
- temp = 0;
- prepare = 0;
- memset(need, 0, 4);
- while (temp < 4)
- {
- if (tmp >= (data_len - equal_count))
- {
- break;
- }
- prepare = (prepare << 6) | (find_pos(data[tmp]));
- temp++;
- tmp++;
- }
- prepare = prepare << ((4-temp) * 6);
- for (i=0; i<3 ;i++ )
- {
- if (i == temp)
- {
- break;
- }
- *f = (char)((prepare>>((2-i)*8)) & 0xFF);
- f++;
- (*len)++;
- }
- }
- *f = '';
- if(data[data_len-1]=='=')
- {
- (*len)--;
- }
- /*
- while(*(--f)=='')
- {
- (*len)--;
- }
- */
- return ret;
- }
- int main(){
- char *former = "hello";
- int len1,len2;
- printf("%sn",former);
- char *after = base64_encode(former, 5,&len1);
- printf("%d %sn",len1,after);
- former = base64_decode(after, len1,&len2);
- printf("%d %sn",len2,former);
- }
来源: http://www.phpxs.com/code/1004231/