C++ char*，const char*，string的相互转换
1. string转const char*
string s ="abc";
constchar* c_s = s.c_str();
2. const char*转string
直接赋值即可
constchar* c_s ="abc";
string s(c_s);
3. string转char*
string s ="abc";
char* c;
constint len = s.length();
c =newchar[len+1];
strcpy(c,s.c_str());
4. char*转string
char* c ="abc";
string s(c);
5. const char*转char*
constchar* cpc ="abc";
char* pc =newchar[100];//足够长