\xxx是当成 3 octal digits吗`?
顺便帮我看下下面程序,感觉这个程序有问题,如果\xxx真的是当成 3 octal digits,那么转成int后会再调用digit,等下这个int会因为> base(等于8)而出错
#include <limits>
#include <stdexcept>
#include <string>
#include <stdio.h>
#if 0
using std::domain_error;
using std::range_error;
using std::string;
#endif
namespace {
inline int digit(char c, int base) {
int value;
switch (c) {
case '0 ': value = 0; break;
case '1 ': value = 1; break;
case '2 ': value = 2; break;
case '3 ': value = 3; break;
case '4 ': value = 4; break;
case '5 ': value = 5; break;
case '6 ': value = 6; break;
case '7 ': value = 7; break;
case '8 ': value = 8; break;
case '9 ': value = 9; break;
case 'a ': case 'A ': value = 10; break;
case 'b ': case 'B ': value = 11; break;
case 'c ': case 'C ': value = 12; break;
case 'd ': case 'D ': value = 13; break;
case 'e ': case 'E ': value = 14; break;
case 'f ': case 'F ': value = 15; break;
default:
throw domain_error(string( "invalid digit "));
}
if (value> =base)
throw domain_error(string( "invalid digit "));
return value;
}
inline char next_char(char const *&p) {
if (*p!= '\\ ') // \ is special; hence '\\ '
return *p++;
else { // 3 octal digits: //@@@@\xxx是不是表示是三个八进制要一起读`
int char_value = digit(p[1], 8)*64
+digit(p[2], 8)*8
+digit(p[3], 8);
if (char_value> std::numeric_limits <char> ::max()
or char_value <std::numeric_limits <char> ::min())
throw domain_error(string( "not a char "));
p += 4; // backslash and 3 octal digits
return char_value;
}
}
void load_first_digit(char const *&s, int &value,
bool &is_negative, int &base) {
char c1 = next_char(s);
is_negative = c1== '- ';
if (c1== '- ' || c1== '+ ')
c1 = next_char(s);
if (c1== '\0 ') { // " ", "- " and "+ " are illegal
throw domain_error(string( "invalid input "));
} else if (c1!= '0 ') {
base = 10;
} else {
char const *p = s;
char c2 = next_char(p);
if (c2== 'x ' || c2== 'X ') { // "0x... "?
base = 16;
s = p;
c1 = next_char(s);
} else { // c2!= 'x ' and c2!= 'X '
base = 8; // I.e., even "0 " is treated as octal
//@@@@@@@@@@@我觉得应该加上c1=c2;
}
}
value = digit(c1, base);
}
} // End unnamed namespace (helper functions)
int atoi(char const *s) {
int value, base;
bool is_negative;
load_first_digit(s, value, is_negative, base);
while (char c = next_char(s)) {
if (value> std::numeric_limits <int> ::max()/base)
throw range_error(string( "out-of-range "));
value *= base;
int d = digit(c, base);
if (value> std::numeric_limits <int> ::max()-d)
throw range_error(string( "out-of-range "));
value += d;
}
return is_negative? -value: value;
}
int main() {
printf( "atoi(\ "123\ ") = %d\n ", atoi( "123 "));
printf( "atoi(\ "0123\ ") = %d\n ", atoi( "0123 "));
printf( "atoi(\ "0x123\ ") = %d\n ", atoi( "0x123 "));
}
[解决办法]
自己先编译运行了试一下。
