Read Whole Ascii File into C++ Std::String

Read whole ASCII file into C++ std::string [duplicate]

Update: Turns out that this method, while following STL idioms well, is actually surprisingly inefficient! Don't do this with large files. (See: http://insanecoding.blogspot.com/2011/11/how-to-read-in-file-in-c.html)

You can make a streambuf iterator out of the file and initialize the string with it:

#include <string>
#include <fstream>
#include <streambuf>

std::ifstream t("file.txt");
std::string str((std::istreambuf_iterator<char>(t)),
                 std::istreambuf_iterator<char>());

Not sure where you're getting the t.open("file.txt", "r") syntax from. As far as I know that's not a method that std::ifstream has. It looks like you've confused it with C's fopen.

Edit: Also note the extra parentheses around the first argument to the string constructor. These are essential. They prevent the problem known as the "most vexing parse", which in this case won't actually give you a compile error like it usually does, but will give you interesting (read: wrong) results.

Following KeithB's point in the comments, here's a way to do it that allocates all the memory up front (rather than relying on the string class's automatic reallocation):

#include <string>
#include <fstream>
#include <streambuf>

std::ifstream t("file.txt");
std::string str;

t.seekg(0, std::ios::end);   
str.reserve(t.tellg());
t.seekg(0, std::ios::beg);

str.assign((std::istreambuf_iterator<char>(t)),
            std::istreambuf_iterator<char>());

Read file-contents into a string in C++ [duplicate]

Like this:

#include <fstream>
#include <string>

int main(int argc, char** argv)
{

  std::ifstream ifs("myfile.txt");
  std::string content( (std::istreambuf_iterator<char>(ifs) ),
                       (std::istreambuf_iterator<char>()    ) );

  return 0;
}

The statement

  std::string content( (std::istreambuf_iterator<char>(ifs) ),
                       (std::istreambuf_iterator<char>()    ) );

can be split into

std::string content;
content.assign( (std::istreambuf_iterator<char>(ifs) ),
                (std::istreambuf_iterator<char>()    ) );

which is useful if you want to just overwrite the value of an existing std::string variable.

How to read total file line by line and set value to string [duplicate]

If you need to read the whole content of a text file into a std::string, you can use the code below.

The function ReadTextFile uses std::ifstream ::rdbuf to extract the content of the file into a std::stringstream. Then it uses std::stringstream::str to convert into a std::string.

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

bool ReadTextFile(std::string const & fileName, std::string & text)
{
    std::stringstream strStream;
    std::ifstream fileStream(fileName);
    if (!fileStream.is_open())
    {
        return false;
    }
    strStream << fileStream.rdbuf();
    fileStream.close();
    text = strStream.str();
    return true;
}

int main() 
{
    std::string text;
    if (!ReadTextFile("t.txt", text))
    {
        std::cout << "failed" << std::endl;
        return 1;
    }
    std::cout << text << std::endl;
    return 0;
}

A side note: better to avoid using namespace std - see here Why is "using namespace std;" considered bad practice?.

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