Read file-contents into a string in C

Question

Possible Duplicate    What is the best way to slurp a file into a std  string in c          In scripting languages like Perl  it is possible to read a file into a variable in one shot       open FILEHANDLE  file        content  lt FILEHANDLE gt     What would be the most efficient way to do this in C

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There should be no  0 in text files    include lt iostream gt   include lt fstream gt   using namespace std   int main      fstream f FILENAME  fstream  in      string s    getline  f  s    0       cout  lt  lt  s  lt  lt  endl    f close

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This depends on a lot of things  such as what is the size of the file  what is its type  text binary  etc  Some time ago I benchmarked the following function against versions using streambuf iterators - it was about twice as fast   unsigned int FileRead  std  istream  amp  is  std  vector  lt char gt   amp  buff         is read   amp buff 0   buff size          return is gcount       void FileRead  std  ifstream  amp  ifs  string  amp  s         const unsigned int BUFSIZE   64   1024     reasoable sized buffer     std  vector  lt char gt  buffer  BUFSIZE         while  unsigned int n   FileRead  ifs  buffer               s append   amp buffer 0   n

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Like this    include  lt fstream gt   include  lt string gt   int main int argc  char   argv       std  ifstream ifs  myfile txt      std  string content   std  istreambuf iterator lt char gt  ifs                             std  istreambuf iterator lt char gt               return 0      The statement    std  string content   std  istreambuf iterator lt char gt  ifs                             std  istreambuf iterator lt char gt              can be split into  std  string content  content assign   std  istreambuf iterator lt char gt  ifs                      std  istreambuf iterator lt char gt              which is useful if you want to just overwrite the value of an existing std  string variable

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Here s an iterator-based method   ifstream file  file   ios  binary   string fileStr   istreambuf iterator lt char gt  inputIt file   emptyInputIt back insert iterator lt string gt  stringInsert fileStr    copy inputIt  emptyInputIt  stringInsert

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The most efficient is to create a buffer of the correct size and then read the file into the buffer    include  lt fstream gt   include  lt vector gt   int main         std  ifstream       file  Plop        if  file                              Get the size of the file                     file seekg 0 std  ios  end           std  streampos          length   file tellg            file seekg 0 std  ios  beg                          Use a vector as the buffer             It is exception safe and will be tidied up correctly             This constructor creates a buffer of the correct length             Because char is a POD data type it is not initialized                        Then read the whole file into the buffer                      std  vector lt char gt        buffer length           file read  amp buffer 0  length

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maybe not the most efficient  but reads data in one line    include lt iostream gt   include lt vector gt   include lt iterator gt   main int argc char  argv          read standard input into vector    std  vector lt char gt v std  istream iterator lt char gt  std  cin                        std  istream iterator lt char gt        std  cout  lt  lt   read    lt  lt  v size    lt  lt   chars n

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The most efficient  but not the C   way would be      FILE  f   fopen filename   r           Determine file size    fseek f  0  SEEK END      size t size   ftell f       char  where   new char size       rewind f      fread where  sizeof char   size  f       delete   where     EDIT - 2  Just tested the std  filebuf variant also  Looks like it can be called the best C   approach  even though it s not quite a C   approach  but more a wrapper  Anyway  here is the chunk of code that works almost as fast as plain C does      std  ifstream file filename  std  ios  binary      std  streambuf  raw buffer   file rdbuf        char  block   new char size      raw buffer- gt sgetn block  size      delete   block    I ve done a quick benchmark here and the results are following  Test was done on reading a 65536K binary file with appropriate  std  ios binary and rb  modes                Running 3 tests from 1 test case   ----------  Global test environment set-up   ----------  4 tests from IO   RUN        IO C Kotti         OK   IO C Kotti  78 ms    RUN        IO CPP Nikko         OK   IO CPP Nikko  106 ms    RUN        IO CPP Beckmann         OK   IO CPP Beckmann  1891 ms    RUN        IO CPP Neil         OK   IO CPP Neil  234 ms   ----------  4 tests from IO  2309 ms total    ----------  Global test environment tear-down              4 tests from 1 test case ran   2309 ms total     PASSED    4 tests

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

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