How to write std::string to file?

Question

I want to write a std::string variable I am accepting from the user to a file. I tried using the write() method and it writes to the file. But when I open the file I see boxes instead of the string.

The string is only a variable length single word. Is std::string suitable for this or should I use a character array or something.

ofstream write; std::string studentName, roll, studentPassword, filename;   public:  void studentRegister() {     cout<<"Enter roll number"<<endl;     cin>>roll;     cout<<"Enter your name"<<endl;     cin>>studentName;     cout<<"Enter password"<<endl;     cin>>studentPassword;       filename = roll + ".txt";     write.open(filename.c_str(), ios::out | ios::binary);      write.put(ch);     write.seekp(3, ios::beg);      write.write((char *)&studentPassword, sizeof(std::string));     write.close();` } 

Answer 1

You're currently writing the binary data in the string-object to your file. This binary data will probably only consist of a pointer to the actual data, and an integer representing the length of the string.

If you want to write to a text file, the best way to do this would probably be with an ofstream, an "out-file-stream". It behaves exactly like std::cout, but the output is written to a file.

The following example reads one string from stdin, and then writes this string to the file output.txt.

#include <fstream> #include <string> #include <iostream>  int main() {     std::string input;     std::cin >> input;     std::ofstream out("output.txt");     out << input;     out.close();     return 0; } 

Note that out.close() isn't strictly neccessary here: the deconstructor of ofstream can handle this for us as soon as out goes out of scope.

For more information, see the C++-reference: http://cplusplus.com/reference/fstream/ofstream/ofstream/

Now if you need to write to a file in binary form, you should do this using the actual data in the string. The easiest way to acquire this data would be using string::c_str(). So you could use:

write.write( studentPassword.c_str(), sizeof(char)*studentPassword.size() ); 

Answer 2

Assuming you're using a std::ofstream to write to file, the following snippet will write a std::string to file in human readable form:

std::ofstream file("filename"); std::string my_string = "Hello text in file\n"; file << my_string;