16进制字符串转换为整型

#include<iostream>
using namespace std;

int char_16_to_int(char * str)
{
if (str == NULL)	
	     return 0;
int sum = 0;
while(*str != '\0')
{
	if (*str<='9' && *str>='0') sum = sum *16 + int(*str - '0');
  if (*str<='F' && *str>='A') sum = sum *16 + int(*str - 'A')+10;
  str++;
}
return sum;
}

int main()
{
	char  str[] ="123";
	int a= char_16_to_int(str);
	cout<<"a="<<a<<endl;
}