Base64编码说明
  Base64编码要求把3个8位字节(3*8=24)转化为4个6位的字节(4*6=24),之后在6位的前面补两个0,形成8位一个字节的形式。

  如果剩下的字符不足3个字节,则用0填充,输出字符使用'=',因此编码后输出的文本末尾可能会出现1或2个'='。

  为了保证所输出的编码位可读字符,Base64制定了一个编码表,以便进行统一转换。

  编码表的大小为2^6=64,这也是Base64名称的由来。


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" alt="" />

base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";//26 + 26 + 10 + 2 
  原型:extern int isalnum(int c);
 
  功能:判断字符变量c是否为字母或数字
  说明:当c为数字0-9或字母a-z及A-Z时,返回非零值,否则返回零。
  

#include <syslib.h>/* 包含 <ctype.h> */
#include <ctype.h> /* 包含 <ctype.h> */
main()/* “主”函数 */
{
int c; /* 整数 c; */
clrscr(); // 清屏() 外语全称加缩写:CLeaR SCReen
c='a';/* 变量赋值 */
printf("%c:%s\n",c,isalnum(c)?"yes":"no");/* “格式输出”(外语全称加缩写:printf) */
c='';/* 变量赋值 */
printf("%c:%s\n",c,isalnum(c)?"yes":"no");
c='@';/* 变量赋值 */
printf("%c:%s\n",c,isalnum(c)?"yes":"no");
getchar();/* 获取字符();*/
return ;/* 返回 零; 正常退出 */
}

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