判断是不是纯数字字符串

 1     bool IsAllDigit(const std::string &sConnect)
 2     {
 3         if (sConnect.empty() )
 4         {
 5             return false;
 6         }
 7 
 8         std::string _sConnect = sConnect;
 9         if (_sConnect[0] == ‘-‘)
10         {
11             //此处-1是为了不被最后一位结束符影响，可以不-1
12             _sConnect = sConnect.substr(1,sConnect.length() - 1);
13             14         }
15         if (_sConnect.empty() )
16         {
17             return false;
18         }
19 
20         for (size_t i = 0; i < _sConnect.length(); i++)
21         {
22             if (_sConnect[i] < ‘0‘ || _sConnect[i] > ‘9‘)
23             {
24                 return false;
25             }
26         }
27 
28         return true;
29     }