C语言中关于进制转化问题

Question

请问如何用htoi函数将十六进制组成的字符串转化成十进制数（前面可能包含0X或0x)

Answer 1

int htoi(const char *s)
{
if( !s )return 0;

if( *s == '0' )
{
    s++;
    if( *s == 'x' || *s == 'X' )s++;
}

int n = 0;
while( *s )
{
    n <<= 4;
    if( *s <= '9' )
        n |= ( *s & 0xf );
    else
        n |= ( (*s & 0xf) + 9 );
    s++;
}
return n;

}