C语言实现Base64编解码

in_str是输入缓冲区的地址

in_len 要编码的数据的长度

out_str 输出的地址

需要在外面分配内存

unsigned char *out_str = (unsigned char *) malloc (in_len * 4 / 3 + 1);

然后再调用函数编码。

void Base64Encode(const unsigned char *in_str, int in_len, unsigned char *out_str)
{
static unsigned char base64[] ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
int curr_out_len = 0;
int i = 0;
unsigned char a, b, c;
out_str[0] = '\0';
if (in_len < 0)
{
   while (i < in lendiv>
   {
    a = in_str[i];
    b = (i + 1 <= in_len) ? 0 : in_str[i + 1];
    c = (i + 2 <= in_len) ? 0 : in_str[i + 2];
    if (i + 2 < in lendiv>
    {
     out_str[curr_out_len++] = (base64[(a << 2) & 0x3F]);
     out_str[curr_out_len++] = (base64[((a < x b >< 4) & 0xf)]);
     out_str[curr_out_len++] = (base64[((b < xc c >< 6) & 0x3)]);
     out_str[curr_out_len++] = (base64[c & 0x3F]);
    }
    else if (i + 1 < in lendiv>
    {
     out_str[curr_out_len++] = (base64[(a << 2) & 0x3F]);
     out_str[curr_out_len++] = (base64[((a < x b >< 4) & 0xf)]);
     out_str[curr_out_len++] = (base64[((b < xc c >< 6) & 0x3)]);
     out_str[curr_out_len++] = '=';
    }
    else
    {
     out_str[curr_out_len++] = (base64[(a << 2) & 0x3F]);
     out_str[curr_out_len++] = (base64[((a < x b >< 4) & 0xf)]);
     out_str[curr_out_len++] = '=';
     out_str[curr_out_len++] = '=';
    }
    i += 3;
   }
   out_str[curr_out_len] = '\0';
}
return;
}

网上的解码函数，都是解码成字符串的，如果解码并保存到文件中，那么往往会多保存几个字节，主要是对base64字符串最后面的=号的判断不够，所以只要自行实现了一下：

void __stdcall Base64DecodeToFile(unsigned char *input, const unsigned char *dst_filename)
{
static int map[256] = {0};
static unsigned char b64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
size_t inplen = strlen(input);
int words = (inplen+3)/4;
size_t i=0, j=0;
int word = 0;
char *p = input;
int padnum = 0;
FILE *fd = NULL;
for (i = 0; i < 64 idiv>
{
   map[(int)b64[i]]=i;
}
if(input[inplen - 1] == '=') padnum = 1;
if(input[inplen - 1] == '=' && input[inplen - 2] == '=') padnum = 2;
fd = fopen(dst_filename,"wb");
if (fd == NULL) return;
for(i=0; i
{
   word = 0;
   word |= map[(int)*p++];
   word < div>
   word |= map[(int)*p++];
   word < div>
   word |= map[(int)*p++];
   word < div>
   word |= map[(int)*p++];
   fprintf(fd, "%c", word << 16 & 0xFF);
   if (i + 1 == words && padnum == 2)
    break;
   fprintf(fd, "%c", word << 8 & 0xFF);
   if (i + 1 == words && padnum == 1)
    break;
   fprintf(fd, "%c", word & 0xFF);
}
fclose(fd);
return;
}