CODEWITHSUNDEEP
c++stringstream
Roddy
Roddy

Reputation: 68114

How to read entire stream into a std::string?

I'm trying to read an entire stream (multiple lines) into a string.

I'm using this code, and it works, but it's offending my sense of style... Surely there's an easier way? Maybe using stringstreams?

void Obj::loadFromStream(std::istream & stream)
{ 
  std::string s;

  std::streampos p = stream.tellg();  // remember where we are

  stream.seekg(0, std::ios_base::end); // go to the end
  std::streamoff sz = stream.tellg() - p;  // work out the size
  stream.seekg(p);        // restore the position

  s.resize(sz);          // resize the string
  stream.read(&s[0], sz);  // and finally, read in the data.

Actually, a const reference to a string would do as well, and that may make things easier...

const std::string &s(... a miracle occurs here...)

Upvotes: 100

Views: 88988

Answers (7)

Vahag Chakhoyan
Vahag Chakhoyan

Reputation: 779

What about to use getline with delimiter? The next code helps me to read whole std::cin into string on ubuntu with g++-10.

#include <iostream>
#include <string>

using namespace std;

int main() {
    string s;

    getline(cin, s, {}); //the whole stream into variable s

    return 0;
}

Upvotes: 1

user7223715
user7223715

Reputation: 31

Perhaps this 1 line C++11 solution:

std::vector<char> s{std::istreambuf_iterator<char>{in},{}};

Upvotes: 0

wdavilaneto
wdavilaneto

Reputation: 816

Well, if you are looking for a simple and 'readable' way to do it. I would recomend add/use some high level framework on your project. For that I's always use Poco and Boost on all my projects. In this case, with Poco:

    string text;
    FileStream fstream(TEXT_FILE_PATH);
    StreamCopier::copyToString(fstream, text);

Upvotes: 2

Cubbi
Cubbi

Reputation: 47498

How about 

std::istreambuf_iterator<char> eos;
std::string s(std::istreambuf_iterator<char>(stream), eos);

(could be a one-liner if not for MVP)

post-2011 edit, this approach is now spelled

std::string s(std::istreambuf_iterator<char>(stream), {});

Upvotes: 146

Joey Adams
Joey Adams

Reputation: 43410

I'm late to the party, but here is a fairly efficient solution:

std::string gulp(std::istream &in)
{
    std::string ret;
    char buffer[4096];
    while (in.read(buffer, sizeof(buffer)))
        ret.append(buffer, sizeof(buffer));
    ret.append(buffer, in.gcount());
    return ret;
}

I did some benchmarking, and it turns out that the std::istreambuf_iterator technique (used by the accepted answer) is actually much slower. On gcc 4.4.5 with -O3, it's about a 4.5x difference on my machine, and the gap becomes wider with lower optimization settings.

Upvotes: 32

Matteo Italia
Matteo Italia

Reputation: 126957

You could do

std::string s;
std::ostringstream os;
os<<stream.rdbuf();
s=os.str();

but I don't know if it's more efficient.

Alternative version:

std::string s;
std::ostringstream os;
stream>>os.rdbuf();
s=os.str();

Upvotes: 23

wheaties
wheaties

Reputation: 35990

You can try using something from algorithms. I have to get ready for work but here's a very quick stab at things (there's got to be a better way):

copy( istreambuf_iterator<char>(stream), istreambuf_iterator<char>(), back_inserter(s) );

Upvotes: 11

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