Is there a way to read an input string with "ifstream" - c++

Question

Currently my programme takes a string as an input which I access using argc and argv
then I use
FILE *fp, *input = stdin;
fp = fopen("input.xml","w+b");
while(fgets(mystring,100,input) != NULL)
{
fputs(mystring,fp);
}
fclose(fp);
I did this part only to create a file input.xml which I then supply to
ifstream in("input.xml");
string s((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
to get s as a string(basic string).
Is there a way to feed my input directly to ifstream? (i.e feeding a string to ifstream).

Answer 1

Let me get this straight:
You read a string from standard input
You write it to a file
You then read it from the file
And use the file stream object to create a string
That's crazy talk!
Drop the file streams and just instantiate the string from STDIN directly:
string s(
(std::istreambuf_iterator<char>(std::cin)),
std::istreambuf_iterator<char>()
);
Remember, std::cin is a std::istream, and the IOStreams part of the standard library is designed for this sort of generic access to data.
Be aware, though, that your approach with std::istreambuf_iterator is not the most efficient, which may be a concern if you're reading a lot of data.

Answer 2

If I get it right then you want to read all the text provided through standard input into a string.
An easy way to achieve this could be the use of std::getline, which reads all the bytes up to a specific delimiter into a string. If you may assume that it is text content (which does not contain any \0-character), you could write the following:
std::string s;
std::getline(cin,s,'\0');