base64编码和解码的C实现

用C实现的base64编码和解码.

#include <stdlib.h>
#include <stdio.h>
#include <getopt.h>
#include <string.h>
const char *options="hs:t:";
const struct option long_options[]={
    {"help",0,NULL,'h'},
    {"src",1,NULL,'s'},
    {"type",1,NULL,'t'},
    {NULL,0,NULL,0}
};
void help()
{
    printf("author ltw:4/12/2008 d/m/Y\n");
    printf("Usage:\n\tltwbase64 -s string -t e\n\tltwbase64 -s string -t d\n");
    exit(0);
}
static const char Base64[] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
void base64_decode(char *src,char *dst)
{
    char *q=malloc(strlen(src)+1);
    char *p=dst;
    char *temp=q;
    char *s=src;
    int len=strlen(src),i;
    memset(q,0,strlen(src)+1);
    while(*s)
    {
        if(*s>='A'&&*s<='Z') *temp=*s-'A';
        else if(*s>='a'&&*s<='z') *temp=*s-'a'+26;
        else if(*s>='0'&&*s<='9') *temp=*s-'0'+52;
        else if(*s=='+') *temp=62;
        else if(*s=='/') *temp=63;
        else if(*s=='=') *temp=-1;
        else
        {
            printf("\n%c:Not a valid base64 string\n",*s);
            exit(0);
        }
        ++s;
        ++temp;
    }
    for(i=0;i<len-4;i+=4)
    {
        *p++=(*(q+i)<<2)+(*(q+i+1)>>4);
        *p++=(*(q+i+1)<<4)+(*(q+i+2)>>2);
        *p++=(*(q+i+2)<<6)+(*(q+i+3));
    }
    if(*(q+i+3)!=-1)
    {
        *p++=(*(q+i)<<2)+(*(q+i+1)>>4);
        *p++=(*(q+i+1)<<4)+(*(q+i+2)>>2);
        *p++=(*(q+i+2)<<6)+*(q+i+3);
    }
    else if(*(q+i+2)!=-1)
    {
        *p++=(*(q+i)<<2)+(*(q+i+1)>>4);
        *p++=(*(q+i+1)<<4)+(*(q+i+2)>>2);
        *p++=(*(q+i+2)<<6);
    }
    else if(*(q+i+1)!=-1)
    {
        *p++=(*(q+i)<<2)+(*(q+i+1)>>4);
        *p++=(*(q+i+1)<<4);
    }
    else
    {
        printf("Not a valid base64 string\n");
        exit(0);
    }
    *p=0;
    free(q);
}
void base64_encode(const char *src,char *dst)
{
    int i=0;
    char *p=dst;
    int d=strlen(src)-3;
    //for(i=0;i
    for(i=0;i<=d;i+=3)
    {
        *p++=Base64[((*(src+i))>>2)&0x3f];
        *p++=Base64[(((*(src+i))&0x3)<<4)+((*(src+i+1))>>4)];
        *p++=Base64[((*(src+i+1)&0xf)<<2)+((*(src+i+2))>>6)];
        *p++=Base64[(*(src+i+2))&0x3f];
    }
    if((strlen(src)-i)==1)
    {
        *p++=Base64[((*(src+i))>>2)&0x3f];
        *p++=Base64[((*(src+i))&0x3)<<4];
        *p++='=';
        *p++='=';
    }
    if((strlen(src)-i)==2)
    {
        *p++=Base64[((*(src+i))>>2)&0x3f];
        *p++=Base64[(((*(src+i))&0x3)<<4)+((*(src+i+1))>>4)];
        *p++=Base64[((*(src+i+1)&0xf)<<2)];
        *p++='=';
    }
    *p='\0';
}
int main(int argc,char **argv)
{
    opterr=0;
    char option;
    char *src=malloc(100);
    char *dst;
    char type;
    int s=0,t=0;
    while((option=getopt_long(argc,argv,options,long_options,NULL))!=-1)
    {    
        switch(option)
        {
            case 'h':
                help();
                break;
            case 's':
                if(strlen(optarg)>99)
                    help();
                strncpy(src,optarg,strlen(optarg));
                *(src+strlen(optarg))='\0';
                s=1;
                break;
            case 't':
                type=optarg[0];
                t=1;
                break;
            case '?':
                break;
            default:
                break;
        }
        
    }
    dst=malloc(((strlen(src)+2)*4/3)+1);
    if(t&&s&&type=='e')
    {
        base64_encode(src,dst);
        printf("%s\n",dst);
    }
    else if(t&&s&&type=='d')
    {
        base64_decode(src,dst);
        printf("%s\n",dst);
    }
    else
        help();
    free(dst);
}