base64编码解码的实现

char*  ch64=”ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/”;

unsigned char *encode(unsigned char *src,int srclen)
{
 int n,buflen,i,j;
 int pading=0;
 unsigned char *buf;
 static unsigned char *dst; 

 buf=src;
 buflen=n=srclen;
 if(n%3!=0)  /* pad with ‘=’ by using a temp buffer */
 {
  pading=1;
  buflen=n+3-n%3;
  buf=malloc(buflen+1);
  memset(buf,0,buflen+1);
  memcpy(buf,src,n);
  for(i=0;i<3-n%3;i++)
   buf[n+i]=’=';
 }
 dst=malloc(buflen*4/3+1);
 memset(dst,0,buflen*4/3+1);
 for(i=0,j=0;i<buflen;i+=3,j+=4)
 {
  dst[j]=(buf[i]&0xFC)>>2;
  dst[j+1]=((buf[i]&0×03)<<4) + ((buf[i+1]&0xF0)>>4);
  dst[j+2]=((buf[i+1]&0x0F)<<2) + ((buf[i+2]&0xC0)>>6);
  dst[j+3]=buf[i+2]&0x3F; 
 }
 for(i=0;i<buflen*4/3;i++) /* map 6 bit value to base64 ASCII character */
  dst[i]=ch64[dst[i]];
 if(pading)
  free(buf);
 return dst;
}

unsigned char *decode(unsigned char *src)
{
 int n,i,j;
 unsigned char *p;
 static unsigned char *dst; 

 n=strlen(src);
 for(i=0;i<n;i++) /* map base64 ASCII character to 6 bit value */
 {
  p=strchr(ch64,src[i]);
  if(!p)
   break;
  src[i]=p-ch64;
 }
 dst=malloc(n*3/4+1);
 memset(dst,0,n*3/4+1);
 for(i=0,j=0;i<n;i+=4,j+=3)
 {
  dst[j]=(src[i]<<2) + ((src[i+1]&0×30)>>4);
  dst[j+1]=((src[i+1]&0x0F)<<4) + ((src[i+2]&0x3C)>>2);
  dst[j+2]=((src[i+2]&0×03)<<6) + src[i+3];
 }
 return dst;
}

void main()
{
// char *src=”zhangwu张武”;
 char src[]={’1′,’2′,’3′,0,’a',’b',’*',0,’A',’B',’$'};
 unsigned char *dst1;
 unsigned char *dst2;
 unsigned int i;

 dst1=encode(src,11); /* the second parameter must accord with the first one */
 printf(“%s\n”,dst1);
 dst2=decode(dst1); 
 for(i=0;i<_msize(dst2);i++)
  printf(“%c”,dst2[i]);

 free(dst1);
 free(dst2);
}