二级指针开辟内存的写法

#include 

using namespace std;

void newMem(string str, char **cp) {
   size_t size = str.size();
   *cp = new char[size + 1];
   memcpy(*cp, str.c_str(), size + 1);
}

int main()
{
   string str = "hello";
   char *out = nullptr;
   newMem(str, &out);
   cout << out << endl;
   int i = 0;
   while(out[i] != '\0') {
      printf("%c, ", out[i]);
      ++i;
   }
   delete [] out; //开辟了char数组，释放时也应该是数组释放，可以使用valgrind检测出来：valgrind --tool=memcheck ./main

   return 0;
}

void copyStringOut(const std::string& src, char** dest)
{
   try {
      *dest = new char[src.size() + 1]; // +1 for NUL
      src.copy(*dest, src.size());
      (*dest)[src.size()] = '\0';
   } catch(const std::exception&) {
      *dest = NULL;
      throw;
   }
}