C语言实现Base64编码解码

Encode

static const char base[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
bool base64_encode(const char * p, char **outptr, int length,int* outlen)
{
	int j = 0;
	int flag=0;
	char *output;
	char *base64;
	base64 = output = (char *)malloc(length * 4 / 3 + 4);
	const char *str = p;
	unsigned char ibuf[3];
	unsigned char obuf[4];
	int insize = length;
	while (insize >0)
	{
		for (j = flag=0; j < 3; j++)
		{
			if (insize > 0) {
				flag ++;
				ibuf[j] = (unsigned char)*str;
				str++;
				insize--;
			}
			else
			{
				ibuf[j] = 0;
			}
		}
		obuf[0] = (unsigned char)((ibuf[0] & 0xfc) >> 2);
		obuf[1] = (unsigned char)((ibuf[0] & 0x03) << 4) | ((ibuf[1] & 0xf0) >> 4);
		obuf[2] = (unsigned char)((ibuf[1] & 0x0f) << 2) | ((ibuf[2] & 0xc0) >> 6);
		obuf[3] = (unsigned char)(ibuf[2] & 0x3f);
		switch (flag)
		{
		case 1:
			snprintf(output,5,"%c%c==", base[obuf[0]], base[obuf[1]]);
			break;
		case 2:
			snprintf(output, 5, "%c%c%c=", base[obuf[0]], base[obuf[1]], base[obuf[2]]);
			break;
		default:
			snprintf(output, 5, "%c%c%c%c", base[obuf[0]], base[obuf[1]], base[obuf[2]], base[obuf[3]]);
			break;
		}
		output += 4;
	}
	*output = '';
	*outptr = base64;
	*outlen= strlen(base64);
	return true;
}

Decode

unsigned char buf_to_index(const char c)
{
	char i = 0;
	while (*base!= EOF)
	{
		if (base[i] == c)
		{
			return (unsigned char)(i);
		}
		i++;
	}
}
bool base64_decode(const char * p, char **outptr, int length, int* outlen)
{
	const char* str = p;
	int insize = length;
	int j = 0;
	char* output;
	char* base64;
	int len = length / 4 * 3;
	output = base64 = (char*)malloc(len);
	unsigned char ibuf[4];
	unsigned char obuf[3];
	int flag = 0;
	while (insize>0)
	{
		for (j = 0; j < 4; j++)
		{
			if (*str=='=')
			{
				flag++;
			}
			ibuf[j] = buf_to_index(*str);
			str++;
			insize--;
		}
		obuf[0] = (ibuf[0]<<2)|((ibuf[1]&0x30)>>4);
		obuf[1] = ((ibuf[1] & 0x0F) <<4)| ((ibuf[2] & 0x3C)>> 2);
		obuf[2] = ((ibuf[2] & 0x03) <<6) | (ibuf[3]);

		snprintf(output, 4, "%c%c%c", obuf[0], obuf[1], obuf[2]);
		output += 3;
	}
	switch (flag)
	{
	case 1:
		len -= 1;
		break;
	case 2:
		len -= 2;
		break;
	default:
		break;
	}
	*output = '';
	*outptr = base64;
	*outlen = len;
	return true;
}