Writing stringstream contents into ofstream

Question

I'm currently using std::ofstream as follows:

std::ofstream outFile;
outFile.open(output_file);

Then I attempt to pass a std::stringstream object to outFile as follows:

GetHolesResults(..., std::ofstream &outFile){
  float x = 1234;
  std::stringstream ss;
  ss << x << std::endl;
  outFile << ss;
}

Now my outFile contains nothing but garbage: "0012E708" repeated all over.

In GetHolesResults I can write

outFile << "Foo" << std:endl; 

and it will output correctly in outFile.

Any suggestion on what I'm doing wrong?

Solution 1

You can do this, which doesn't need to create the string. It makes the output stream read out the contents of the stream on the right side (usable with any streams).

outFile << ss.rdbuf();

Solution 2

If you are using std::ostringstream and wondering why nothing get written with ss.rdbuf() then use .str() function.

outFile << oStream.str();

Solution 3

When passing a stringstream rdbuf to a stream newlines are not translated. The input text can contain \n so find replace won't work. The old code wrote to an fstream and switching it to a stringstream losses the endl translation.

Solution 4

I'd rather write ss.str(); instead of ss.rdbuf(); (and use a stringstream).

If you use ss.rdbuf() the format-flags of outFile will be reset rendering your code non-reusable. I.e., the caller of GetHolesResults(..., std::ofstream &outFile) might want to write something like this to display the result in a table:

outFile << std::setw(12) << GetHolesResults ...

...and wonder why the width is ignored.

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Comments

[Alex Bitek]

This should be a comment not an answer because you haven't told how to write a std::stringstream to a std::ofstream

[Javi]

I'm curious: why this solution works with std::stringstream but not with std::ostringstream? In the second case I am getting an empty file.

[abcd]

your answer led me to the following realization: to get a char array from ss, you can do ss.str().c_str(). (just posting here for the benefit of newbies who stumble on this in the future.)

[Nasir]

@Digital_Reality, thanks! nothing was getting written when i used rdbuff. What is the reason for this?

[S.R]

@JaviV because you can only write to std::oANYSTREAM and only read from std::iANYSTREAM. There will be no sense for output_stream if it would have also read operations. If you need both just use std::ANYSTREAM and you are home :)