After reading through all the documentation and examples I could read, I still can't get the following piece of code to work . I assume that when you pass  a new_file_size  and a path  to the mapped_file_params class , it will then open the file at the location desired when I call the constructor of mapped_file with the mapped_file_params object in parameter.

 But the only thing it does is to create a file with a weird name , like "%F8/134" in the project working directory, not where I told it to.

Maybe I'm wrong and one should create file before specifying it to the mapped_file? After reading the doc, I was under the assumption that it created a new file when you fill in the new_file_size param. and specifies the filename.

Anyone experienced this before? Any advice on how to resolve this?

Here's the code: 

boost::iostreams::mapped_file_params param(filename); // filename is a std::string with the correct path

param.new_file_size = sizeNeeded; // sizeNeeded is the size of the data

param.length = sizeNeeded;

boost::iostreams::mapped_file fileMap(param); // at this point the file is created

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