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Updated June 16, 2023Introduction to C++ fstreamIn C++, the concept of the fstream is used for the reading and writing on the file system. In very simple and technical words, it can do dual work, which means it has ofstream and ifstream. So if the file is not there on which we are going to write some contents, then the fstream can write the contents on the file, and at the same time, it also allows us to open the file and display the contents. We should use this if we know that we will create, read and write content on the file.Syntax:Below is a simple syntax for the fstream in C++. In the example below, we are first getting or creating a file; we can give any name to the file we are creating here. Second, we are writing some content to the file. In the same way, we can read the file content with the help of the getline function in a while loop.ofstream creatMyFile(AnyFileName);creatMyFile How fstream work in C++?We already have a package like ifstream and ofstream, but they can either read and write the file, but what do we do in case we want to perform read and write the file? So for that case, we have the fstream c++ package.We can create a file if the file does not exist.First, we can create a file instance with code like “ofstream of”; here, of will be used as the instance.Next, we can pass any file name we want to create, like “open(any filename);”.Finally, we can write the contents on the file like cout If needed, we can also read the file’s contents with the help of the getline functions to read data line by line.Examples of C++ fstreamGiven below, we have three significant examples of the fstream of C++. In the examples, we show how we create an empty file, write some contents on the file, and then again read the same file by printing all the contents.Example #1Code://Importing the package iostream#include //Importing the package fstream#include //Importing the string package for string related works#include using namespace std;int main () {string ln;//Creating a file with name test.txt ,if not existsifstream testFile ("test.txt");//Checking the file opening conditionif (testFile.is_open()){//Running a while loop and fetch all the contents line by linewhile ( getline (testFile,ln) ){//Printing the output of the file contentscout Output:Example #2Code://Importing the package iostream#include //Importing the package fstream#include //Importing the package string for string related work#include using namespace std;int main () {// This code will create a file with name test.txtofstream creatMyFile("test.txt");// Here we are writing contents to the filecreatMyFile Output:Example #3Code://Importing the package fstream#include //Importing the package iostream#include using namespace std;int main () {char subject[200];// Here we are opening the file in the write mode for operationsofstream of;//Open the file and create the file if not existsof.open("test.txt");//Writing the the data to the file which we have createdcout > subject;cin.ignore();// Here we are again writing some input data to fileof > subject;// Writing some data to itcout >

The file specification dictionary /F (name) % The file name for export /EF ... >> % Embedded file stream dictionary >> ] >> >> >>For example: [ /NamespacePush pdfmark [ /_objdef {fstream} /type /stream /OBJ pdfmark [ {fstream} /Type /EmbeddedFile >> /PUT pdfmark [ {fstream} (Simulating file content here) /PUT pdfmark [ /Name (Unicode Unique Name)% e.g., feff 0041 0073> is Unicode for "As" /FS /Type /Filespec /F (myfile.txt) /EF /F {fstream} >> >> /EMBED pdfmark [ {fstream} /CLOSE pdfmark [ /NamespacePop pdfmarkDistiller command line options to enable file embedding¶Acrobat Distiller 8.1 and later permit PostScript operators to access only font files, char map files, and files within the installation directory. In contrast, Acrobat Distiller 8.0 and earlier permit unlimited file access. This change was introduced to address security concerns.To reflect the change in file access behavior, the Distiller command line option (Windows and UNIX ) or user preference (Mac) related to file embedding were also reversed, but in the opposite direction. In Acrobat Distiller 8.1 and later, these Distiller command line options enable unlimited file access, overriding the normal mode of restricting file access. In Acrobat Distiller 8.0 and earlier, these command line options specified limited file access (restricted to fonts, char map files, and files within the installation directory), overriding the normal mode of unrestricted file access.To use the EMBED pdfMark directive to embed files other than fonts and char maps, follow these version-specific guidelines on invoking Acrobat Distiller:Acrobat Distiller 8.1 and later: Include the Distiller command line option (Windows and UNIX ) or user preference (Mac) that enables unlimited file access. You should be aware that such unlimited access can pose security problems. The following Windows command line invokes Acrobat Distiller with the option that specifies unlimited file access.acrodist -F MyFileContainingPDFMarkEMBED.psAcrobat Distiller 8.0 and earlier: Omit the file-embedding Distiller command line option (Windows and UNIX ) or user preference (Mac) that restricts unlimited file access. The following Windows command line invokes Acrobat Distiller. The omission of the -F command line option specifies unlimited file access.acrodist MyFileContainingPDFMarkEMBED.psTo summarize, in 8.0 and earlier the command line switch “restricts” unlimited file access. In 8.1 and later the command line switch “enables” unlimited file access.For information on the file-embedding Distiller command line option (Windows and UNIX ) and user preference (Mac), see the Distiller API Reference.Graphics encapsulation (BP, EP, SP)¶Distiller allows a PostScript language program to specify that a given set of graphical operations should be encapsulated and treated as a single object. The pdfmark features BP (Begin Picture) and EP (End Picture) enclose a set of graphic operations. The SP (Show Picture) pdfmark indicates where to insert an object (which may be inserted in more than one place).The syntax for the graphics encapsulation commands is as follows:[ /_objdef {objname} /BBox [xll yll xur yur] /BP pdfmark ... page marking instructions ... [ /EP pdfmark [ {objname} /SP pdfmarkThe _objdef {objname} key–value pair in the BP pdfmark names the picture objname. Any subsequent pdfmark can refer to this object.NoteGraphics names are

Subject;cout Output:Advantages of C++ fstreamGiven below are the advantages mentioned :It can perform dual work like it can create a file and simultaneously allows you to write the file’s contents.One of the most important things about it is it allows us to use the concept of internalization and localization.It gives us a complete object-oriented approach, because of which we can reuse the features many times.Because it has a feature where if the file does not exist, it will create the file for us instead of throwing an error.ConclusionThis tutorial showed the basic concept of the stream and its syntax. We also focused on the working and some of the essential advantages of using the concept of the fstream. We noticed some of important examples also.Recommended ArticlesWe hope that this EDUCBA information on “C++ fstream” was beneficial to you. You can view EDUCBA’s recommended articles for more information.C++ any()Type Casting in C++C++ BitsetC++ iostream

The top of the file while pointer_location >= 0: # Move the file pointer to the location pointed by pointer_location read_obj.seek(pointer_location) # Shift pointer location by -1 pointer_location = pointer_location -1 # read that byte / character new_byte = read_obj.read(1) # If the read byte is new line character then it means one line is read if new_byte == b'\n': # Fetch the line from buffer and yield it yield buffer.decode()[::-1] # Reinitialize the byte array to save next line buffer = bytearray() else: # If last read character is not eol then add it in buffer buffer.extend(new_byte) # As file is read completely, if there is still data in buffer, then its the first line. if len(buffer) > 0: # Yield the first line too yield buffer.decode()[::-1]def main(): print('**** Read a file in reversed order line by line ****') # Iterate over the file in reverse order using for loop for line in read_reverse_order('sample.txt'): print(line) print('**** Get a list of all lines in file in reversed order****') # Get a list of lines in file as reverse order lines_in_reverse_order = read_reverse_order_2('sample.txt') # iterate over the lines in list for line in lines_in_reverse_order: print(line)if __name__ == '__main__': main() **** Read a file in reversed order line by line ****This is the end of fileDummy Line CDummy Line BDummy Line AIt contains sample textHello this is a sample file**** Get a list of all lines in file in reversed order****This is the end of fileDummy Line CDummy Line BDummy Line AIt contains sample textHello this is a sample file Answer by Orion Truong Note: We have already created a file codesdope.txt with text already written on it.,File Handling is the storing of data in a file using a program. It enables us to create, update, read, and delete the files stored on the local file system through our program.,These are the data types used for file handling from the fstream library : ,The fstream library allows us to work with files. There are three classes included in fstream library, which are used to create, write or read the files. //C++ code#include#include#includeusing

In this ostensibly meaningless memetic montage:The “broken” challenge PDF rendered using the modified version of mutool.Searching Google for the LMGTFY string will take you to Didier Stevens’ excellent article describing the PDF stream format in detail, including how PDF objects are numbered and versioned. One important factor is that two PDF objects can have the same number but different versions.The first hint on the page identifies PDF object 1337, so that is probably important. The figures in Stevens’ article alone, juxtaposed to a hexdump of the broken PDF’s stream objects, provide a clear depiction of what was changed.Didier Stevens’ annotated diagram of a PDF stream object.5 0 obj>^Fstream⋮endstreamendobjA PDF stream object in the challenge PDF.As the hints suggest, the PDF specification only allows for six whitespace characters: \0, \t, \n, \f, \r, and space. The version of mutool in the ZIP was modified to also allow ACK (0x06) to be used as a seventh whitespace character! Sure enough, on the twelfth line of the file we see:>>^FstreamThat “^F” is an ACK character, where the PDF specification says there should be whitespace! All of the PDF object streams are similarly broken. This can be fixed with:bbe -e "s/\x06stream\n/\nstream\n/" -o challenge_fixed.pdf challenge.pdfSolving the PuzzleIs fixing the file strictly necessary to solve the challenge? No, the flag may be found in PDF object 0x1337 using a hex editor4919 0 obj>^Fstreamx^MËA^N@0^PFá}OñëÆÊÊ X;^BaNN£#áöº~ßss^ONÅ6^Qd/°^[¤(öHû }^L^V k×E»dfcM^[køôië^N ^G~}Õ\°L3^BßÅ^Z÷^CÛ!Ûendstreamendobj4919 1 obj>^Fstream…endstreamendobjand manually decoding the stream contents. Binwalk will even automatically decode the first stream because it can decode

As a readelf hint that we’ll get to later.The remainder of the Ruby script is embedded within a PDF object stream—the “9999 0 obj” line—, which can contain arbitrary data ignored by PDF. But what of the remainder of the PDF? How does that not affect the Ruby script?9999 0 obj>^Fstream=endport = 8080if ARGV.length > 0 then port = ARGV[0].to_iendhtml=DATA.read().encode('UTF-8', 'binary', :invalid => :replace, :undef => :replace).split(//)[0]+"\n"v=TCPServer.new('',port)print "Server running at listen on a different port, re-run with the desired port as a command-line argument.\n\n"⋮__END__Ruby has a feature where the lexer will halt on the __END__ keyword and effectively ignore everything thereafter. Sure enough, this curious PDF has such a symbol, followed by the end of the encapsulating PDF object stream and the remainder of the PDF.This is a Ruby/PDF polyglot, and you can turn any PDF into such a polyglot using a similar method. If your script is short enough, you don’t even need to embed it in a PDF stream object. You can just prepend all of it before the %PDF-1.5 header. Although some PDF parsers will complain if the header is not found within the first 1024 bytes of the file.You didn’t think it would be that easy, did you?So let’s be brave and try running the PDF as if it were a Ruby script. Sure enough, it runs a webserver that serves a webpage with a download link for “flag.zip.” Wow, that was easy, right? Inspect the Ruby script further and you’ll see that the download is