c++ - string和char*到底能不能转换呢？

Question

我一直想的是利用C++string类封装的函数的便捷性和linux下的C/API结合来
实现某些方法。可是有个问题出现了，每次碰见string和char*之间的转换的时候极为的尴尬。

  #include <iostream>
  #include <stdio.h>
  #include <unistd.h>
  #include <iostream>
  #include <string>
  #include <sys/types.h>          /* See NOTES */
  #include <sys/socket.h>
  #include <arpa/inet.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  using namespace std;


int main(int argc, char const *argv[])
{
 int fd = open("./ok",O_RDWR);

// char buf[1024];
string buf = new char[1023];
read(fd,const_cast<char*>(buf.c_str()),1024);
cout << buf << endl;
// string buf2 = (string)buf;
cout << buf.find_first_of(" ",0);
cout << "*********" << endl;

return 0;
}

read的第二个参数原本是void，一般使用的时候是用char来做的，把独到的信息存储在buf里面，为了以后方便，我希望在这里直接用一个string来存储信息。
我清楚string和char*并不是兼容的，所以我通过const_cast来转换。
可是尴尬的是并没有读到什么信息。
这是为什么呢？

Answer 1

The content returned by c_str cannot be modified, even if it is cast.
http://www.cplusplus.com/reference/string/string/c_str/

Answer 2

If you use c, you should make good use of the c interface. And judging from your appearance, you can use c++ without learning it at all. Even if you want to write 面向过程风格's c++, you still have to learn it...

string buf = new char[1023];
read(fd,const_cast<char*>(buf.c_str()),1024);

You can replace the above with this,

char buf[1024];
read(fd, buf, 1024); 
// cout <<string(buff)<<endl; // 但是这样你要再转换成string就没必要了，除非你以后还要用到这个值

Also c++ it is not recommended to use forced type conversion, of course the following conversion is purely wrong

// string buf2 = (string)buf;
// 应该是这样调用构造函数
// string buf2 = string(buf);
// 或者隐式调用构造函数
// string buf2 = buf;

Answer 3

char buff[1024]={0};
strncpy(buff,str.c_str(),str.length());//string to char
str.assign(buff);//char to string
可以考虑动态分配buff空间。

Answer 4

As mentioned on the first floor, string::c_str() returns a const char* pointer, which points to the first address of a string object. Since it is a const char* type, of course the content of the address it points to cannot be Modified, so nothing can be read.