C++实现十六进制字符串转换为十进制整数的方法

/*
* 将十六进制数字组成的字符串（包含可选的前缀0x或0X）转换为与之等价的整型值
*/
#include <stdio.h>
#include <math.h>
/* 将十六进制中的字符装换为对应的整数 */
int hexchtoi(char hexch )
{
 char phexch[] = "ABCDEF";
 char qhexch[] = "abcdef";
 int i;
 for(i=0;i<6;i++){
  if((hexch == phexch[i]) || (hexch == qhexch[i]))
   break;
 }
 printf("i=%d",i);
 if(i >= 6){
  return 0; /* 非十六进制字符 */
 }
 return 10+i;
}
int htoi(char s[])
{
 int n=0; /*有n位*/
 int valu=1; /*是否有效*/
 int i=0,j;
 int answer=0;
 /* 有效性检查 */
 if((s[0] == '0') && ((s[1] == 'x') || (s[1] == 'X'))){
  i += 2;
 }
 while((s[i] != '\n')){
  if((s[i] < '0') && (s[i] > '9')){
   if(hexchtoi(s[i]) == 0){
    valu=0;
    break;
   }
  }
  n++;
  i++;
 }
 if(valu != 0){   
  for(j=0;j<n;j++){
   answer += ((int)pow(16,j) * hexchtoi(s[i-j-1]));
  } 
 }
 else
  answer = -1;
 return answer;
}
main()
{
 char *n[] = {"0x7ff0","0x2341"};
 printf("%s is %d\n",n[0],htoi(n[0]));
 printf("%s is %d\n",123);
}