string转成char * 或者const char *

1. string转const char*是比较容易的，直接用函数c_str()即可

string a = "hello";

const char * b = a.c_str();

 

2. 转char * 可以先转为const char * 

string a = "hello";

char * c = new char[a.length()+1];

strncpy(c,a.c_str(),a.length()+1);