ifstream的std :: getline，使用参数字符串或char *

Question

I am using fstream to read or write into a file.

I meet a problem regarding the function ifstream::getline . When I include <string> , then I can pass string as a parameter to the function, if not, I have to pass char* as the parameter. Can someone tell me why?

According to the description of the function, as I understand it, the right parameter waited should be char* . Is the string value converted to a char* here?

Answer 1

String type isn't converted to char* . That's why .c_str() exists. But the std::string type will accept a char* as an initializer.

The two types aren't backwards compatible. std::string 's will accept char* 's but char* 's don't accept std::string 's.

Answer 2

There are two versions of std::getline() :

std::istream::getline(char*, char = '\n'); // member function of istream
std::getline(std::istream&, std::string&, char = '\n'); // free function in <string>

When including the definition of std::istream you obviously get the member function. However, you'll need to include <string> to get the definition of std::string which also comes with its version of std::getline() .