如何将十六进制转换为、二进制、八进制、十进制

void HexToBin(char* hex, char* bin, int n = 20)
{
char a[17][6] = {
"0000 ","0001 ","0010 ","0011 ",
"0100 ","0101 ","0110 ","0111 ",
"1000 ","1001 ","1010 ","1011 ",
"1100 ","1101 ","1110 " ,"1111 " };
int* temp = (int*)malloc(sizeof(int)*n);
memset(temp, 0, n * 4);
char* h = hex;
int i = 0, j = 0, k = 0, g = 0;
while (*h)                      //把十六进制的每一位转换为整数
{
char ch = *h;
if (ch == 'A')temp[i++] = 10;
else if (ch == 'B') temp[i++] = 11;
else if (ch == 'C') temp[i++] = 12;
else if (ch == 'D') temp[i++] = 13;
else if (ch == 'E') temp[i++] = 14;
else if (ch == 'F') temp[i++] = 15;
else temp[i++] = *h - '0';
h++;
}
do
{
while (j < 5)
bin[k++] = a[temp[g] % 16][j++];
j = 0;
} while (i>++g);
free(temp);
}

long long HexToOct(char* hex)
{
long long oct = 0;
long long dec = 0;
char* h = hex;
int p = 0, q = 0, i = 0, g = 0;
int temp[30] = { 0 };
while (*h++) ++p;  //calc hex arrary length
h = hex;
while (*h)                          //把十六进制的每一位转换为整数
{
char ch = *h;
if (ch == 'A')temp[i++] = 10;
else if (ch == 'B') temp[i++] = 11;
else if (ch == 'C') temp[i++] = 12;
else if (ch == 'D') temp[i++] = 13;
else if (ch == 'E') temp[i++] = 14;
else if (ch == 'F') temp[i++] = 15;
else temp[i++] = *h - '0';
h++;
}
i = 0;
while (p)                       //十六进制 --> 十进制
dec += powl(16, --p)*temp[i++];//因为powl的缘故，十六进制不能太大
memset(temp, 0, sizeof(temp));
i = 0;
while (dec)                     //十进制 --> 八进制
{
temp[i++] = (dec % 8);
dec = dec >> 3;
}
while (q < i)
oct += powl(10, q++)*temp[g++];
return oct;
}

long long HexToDec(char* hex)
{
long long dec = 0;
int temp[30] = { 0 };
char* h = hex;
int i = 0, p = 0;
while (*h++) ++p;
while (*hex)
{
char ch = *hex;
if (ch == 'A')temp[i++] = 10;
else if (ch == 'B') temp[i++] = 11;
else if (ch == 'C') temp[i++] = 12;
else if (ch == 'D') temp[i++] = 13;
else if (ch == 'E') temp[i++] = 14;
else if (ch == 'F') temp[i++] = 15;
else temp[i++] = *hex - '0';
hex++;
}
i = 0;
while (p)
dec += powl(16, --p)*temp[i++];
return dec;
}