Read whole ASCII file into C std string

Question

I need to read a whole file into memory and place it in a C   std  string   If I were to read it into a char    the answer would be very simple   std  ifstream t  int length  t open  file txt            open input file t seekg 0  std  ios  end         go to the end length   t tellg                 report location  this is the length  t seekg 0  std  ios  beg         go back to the beginning buffer   new char length         allocate memory for a buffer of appropriate dimension t read buffer  length            read the whole file into the buffer t close                          close file handle         Do stuff with buffer here       Now  I want to do the exact same thing  but using a std  string instead of a char    I want to avoid loops  i e  I don t want to   std  ifstream t  t open  file txt    std  string buffer  std  string line  while t   std  getline t  line          Append line to buffer and go on   t close     Any ideas

User · Answer

I could do it like this   void readfile const std  string  amp filepath std  string  amp buffer       std  ifstream fin filepath c str         getline fin  buffer  char -1        fin close        If this is something to be frowned upon  please let me know why

User · Answer

Update  Turns out that this method  while following STL idioms well  is actually surprisingly inefficient  Don t do this with large files   See  http   insanecoding blogspot com 2011 11 how-to-read-in-file-in-c html   You can make a streambuf iterator out of the file and initialize the string with it    include  lt string gt   include  lt fstream gt   include  lt streambuf gt   std  ifstream t  file txt    std  string str  std  istreambuf iterator lt char gt  t                     std  istreambuf iterator lt char gt        Not sure where you re getting the t open  file txt    r   syntax from  As far as I know that s not a method that std  ifstream has  It looks like you ve confused it with C s fopen   Edit  Also note the extra parentheses around the first argument to the string constructor  These are essential  They prevent the problem known as the  most vexing parse   which in this case won t actually give you a compile error like it usually does  but will give you interesting  read  wrong  results   Following KeithB s point in the comments  here s a way to do it that allocates all the memory up front  rather than relying on the string class s automatic reallocation     include  lt string gt   include  lt fstream gt   include  lt streambuf gt   std  ifstream t  file txt    std  string str   t seekg 0  std  ios  end      str reserve t tellg     t seekg 0  std  ios  beg    str assign  std  istreambuf iterator lt char gt  t                std  istreambuf iterator lt char gt

User · Answer

I figured out another way that works with most istreams  including std  cin   std  string readFile         stringstream str      ifstream stream  Hello World txt        if stream is open                  while stream peek      EOF                        str  lt  lt   char  stream get                      stream close            return str str

User · Answer

I think best way is to use string stream  simple and quick       include  lt fstream gt   include  lt iostream gt   include  lt sstream gt    std  stringstream int main         std  ifstream inFile      inFile open  inFileName      open the input file      std  stringstream strStream      strStream  lt  lt  inFile rdbuf      read the file     std  string str   strStream str      str holds the content of the file      std  cout  lt  lt  str  lt  lt    n     you can do anything with the string

User · Answer

If you happen to use glibmm you can try Glib  file get contents    include  lt iostream gt   include  lt glibmm h gt   int main         auto filename    my-file txt       try           std  string contents   Glib  file get contents filename           std  cout  lt  lt   File data  n   lt  lt  contents  lt  lt  std  endl      catch  const Glib  FileError amp  e            std  cout  lt  lt   Oops  an error occurred  n   lt  lt  e what    lt  lt  std  endl             return 0

User · Answer

You may not find this in any book or site but I found out that it works pretty well   ifstream ifs   filename txt    string s  getline  ifs  s   char  ifs eof

User · Answer

Try one of these two methods   string get file string        std  ifstream ifs  path to file        return string  std  istreambuf iterator lt char gt  ifs                       std  istreambuf iterator lt char gt          string get file string2        ifstream inFile      inFile open  path to file     open the input file      stringstream strStream      strStream  lt  lt  inFile rdbuf     read the file     return strStream str     str holds the content of the file

User · Answer

I don t think you can do this without an explicit or implicit loop  without reading into a char array  or some other container  first and ten constructing the string   If you don t need the other capabilities of a string  it could be done with vector lt char gt  the same way you are currently using a char

User · Answer

There are a couple of possibilities  One I like uses a stringstream as a go-between   std  ifstream t  file txt    std  stringstream buffer  buffer  lt  lt  t rdbuf      Now the contents of  file txt  are available in a string as buffer str     Another possibility  though I certainly don t like it as well  is much more like your original   std  ifstream t  file txt    t seekg 0  std  ios  end   size t size   t tellg    std  string buffer size        t seekg 0   t read  amp buffer 0   size      Officially  this isn t required to work under the C  98 or 03 standard  string isn t required to store data contiguously  but in fact it works with all known implementations  and C  11 and later do require contiguous storage  so it s guaranteed to work with them   As to why I don t like the latter as well  first  because it s longer and harder to read  Second  because it requires that you initialize the contents of the string with data you don t care about  then immediately write over that data  yes  the time to initialize is usually trivial compared to the reading  so it probably doesn t matter  but to me it still feels kind of wrong   Third  in a text file  position X in the file doesn t necessarily mean you ll have read X characters to reach that point -- it s not required to take into account things like line-end translations  On real systems that do such translations  e g   Windows  the translated form is shorter than what s in the file  i e     r n  in the file becomes   n  in the translated string  so all you ve done is reserved a little extra space you never use  Again  doesn t really cause a major problem but feels a little wrong anyway

[c++] Read whole ASCII file into C++ std::string

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