标签：最大 就是 nbsp pre 进制 需求 size a.out std
在互联网上传输二进制数据。一个字节是8位，能表示最大的数是255。但是ASCII表能表示的最大数是127,两者需要转换一下。base64就是将3个8位的数据，转为4个6位的数据。转换后的字符都是可打印字符。一般设置为"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"。当然，你可以根据自己的需求，使用别的可打印字符
下面是参考nginx实现的base64编码和解码
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void base64_encode(u_char* dst, const u_char* src)
{
char basis[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
int len = strlen((char*)src);
while (len > 2)
{
*dst++ = basis[(src[0] >> 2) & 0x3f];
*dst++ = basis[((src[0] & 3) << 4) | (src[1] >> 4)];
*dst++ = basis[((src[1] & 0x0f) << 2) | (src[2] >> 6)];
*dst++ = basis[src[2] & 0x3f];
src += 3;
len -= 3;
}
if (len == 1)
{
*dst++ = basis[src[0] >> 2];
*dst++ = basis[(src[0] & 0x3) << 4];
*dst++ = ‘=‘;
*dst++ = ‘=‘;
}
if (len == 2)
{
*dst++ = basis[src[0] >> 2];
*dst++ = basis[((src[0] & 3) << 4) | (src[1] >> 4)];
*dst++ = basis[(src[1] & 0xf) << 2];
*dst++ = ‘=‘;
}
*dst = ‘\0‘;
}
int base64_decode(u_char* dst, const u_char* src)
{
static u_char basis64[] = {
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 62, 77, 77, 77, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 77, 77, 77, 77, 77, 77,
77, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 77, 77, 77, 77, 77,
77, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77,
77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77, 77
};
int srclen = strlen((char*)src);
int len = 0;
for (; len < srclen; len++)
{
if (src[len] == ‘=‘)
{
break;
}
if (basis64[src[len]] == 77)
{
return -1;
}
}
if ((len >> 2) == 1)
{
return -1;
}
while (len > 3)
{
*dst++ = (u_char)((basis64[src[0]] << 2) | (basis64[src[1]] >> 4));
*dst++ = (u_char)((basis64[src[1]] << 4) | (basis64[src[2]] >> 2));
*dst++ = (u_char)((basis64[src[2]] << 6) | basis64[src[3]]);
src += 4;
len -= 4;
}
if (len > 1)
{
*dst++ = (u_char)((basis64[src[0]] << 2) | (basis64[src[1]] >> 4));
}
if (len > 2)
{
*dst++ = (u_char)((basis64[src[1]] << 4) | (basis64[src[2]] >> 2));
}
*dst = ‘\0‘;
}
int main(int argc, char **argv)
{
u_char szencode[100] = {0};
u_char szdecode[100] = {0};
base64_encode(szencode, (u_char*)argv[1]);
printf("%s\n", szencode);
base64_decode(szdecode, szencode);
printf("%s\n", szdecode);
return 0;
}
./a.out ‘test测试english和and中文chinese‘
dGVzdOa1i+ivlWVuZ2xpc2jlkoxhbmTkuK3mlodjaGluZXNl
test测试english和and中文chinese
标签：最大 就是 nbsp pre 进制 需求 size a.out std
原文地址：https://www.cnblogs.com/zuofaqi/p/9781251.html
