Istream to string conversion with \n characters in C++

Question

how can I convert istream to string, when my istream also includes newline characters and I don't want to escape whitespaces? Thank you.

Do you mean you want the string to contain the literal characters `'\'` and `'n'` instead of a newline? — Joseph Mansfield, Apr 19 '15 at 18:00
Even just asking about "converting" a stream to a string suggests a fundamental misunderstanding. A stream is a flow of data, whereas a string is a container of bytes. The two are entirely different. Did you mean you wish to extract all bytes from the stream into a string, until the stream runs dry (reaches EOF)? Or what? Be specific and precise. — Lightness Races in Orbit, Apr 19 '15 at 18:05
Unformatted input functions? `noskipws`? Initialize it with `istreambuf_iterator`s? — chris, Apr 19 '15 at 18:06

score 0 · Answer 1 · answered Apr 19 '15 at 18:06

If you mean how to copy the whole std::istream into a std::string then there are many ways.

Here is one:

int main()
{
    // here is your istream
    std::ifstream ifs("test.txt");

    // copy it to your string
    std::string s;
    for(char c; ifs.get(c); s += c) {}

    // display
    std::cout << s << '\n';
}

Christophe · Answer 2 · 2015-04-19T18:15:32.297

You can just allocate a string large enough for your whole file and read it at once:

ifstream fd(filename);          // open your stream (here a file stream)
if (!fd)
    exit(1);

fd.seekg(0, ios_base::end);     // go to end of file
size_t filesize = fd.tellg();   // dtermine size to allocate
fd.seekg(0, ios_base::beg);     // go to the begin of your file

string s;                       // create a new string
s.resize(filesize+1);           // reserve enough space to read

fd.read(&s[0], filesize);       // read all the file at one
size_t bytes_read = fd.gcount();  // it could be than less bytes are read
s.resize(bytes_read);           // adapt size

score 0 · Answer 3 · answered Apr 19 '15 at 18:17

You can use a istreambuf_iterator like

#include <iostream>
#include <string>
#include <fstream>

int main()
{
   std::ifstream ifile("test.txt"); // open 
   std::string str(std::istreambuf_iterator<char>(ifile), {}); // initialize
   std::cout << str; // display
}

Istream to string conversion with \n characters in C++

3 Answers3