How to read a file into vector in C

Question

I need to read from a  data or  txt file containing a new float number on each line into a vector    I have searched far and wide and applied numerous different methods but every time I get the same result  of a Main size   of 0 and an error saying  Vector Subscript out of Range   so evidently the vector is just not reading anything into the file   Note  the file is both in the folder and also included in the VS project   Anyway  here s my code    include  lt iostream gt   include  lt fstream gt   include  lt sstream gt   include  lt vector gt   include  lt string gt   using namespace std   int main          vector lt double gt  Main      int count      string lineData      double tmp       ifstream myfile   test data   ios  in        double number         myfile  gt  gt  count      for int i   0  i  lt  count  i              myfile  gt  gt  tmp          Main push back tmp           cout  lt  lt  count             cout  lt  lt   Numbers  n       cout  lt  lt  Main size        for  int i 0  i   Main size   -1   i              cout  lt  lt  Main i   lt  lt    n              cin get         return 0      The result I get is always simply   Numbers  0

User · Answer

Just a piece of advice  Instead of writing   for  int i 0  i   Main size   -1   i         cout  lt  lt  Main i   lt  lt    n       as suggested above  write a   for  vector lt double gt   iterator it Main begin    it  Main end    it         cout  lt  lt   it  lt  lt    n       to use iterators  If you have C  11 support  you can declare i as auto i Main begin    just a handy shortcut though   This avoids the nasty one-position-out-of-bound error caused by leaving out a -1 unintentionally

User · Answer

include  lt iostream gt   include  lt fstream gt   include  lt vector gt  using namespace std   int main     fstream dataFile  string name   word   new word  vector lt string gt  test  char fileName 80   cout lt  lt  Please enter the file name      cin  gt  gt  fileName  dataFile open fileName   if dataFile fail           cout lt  lt  File can not open  n        return 0    cout lt  lt  File opened  n   cout lt  lt  Please enter the word      cin gt  gt word  cout lt  lt  Please enter the new word      cin  gt  gt  new word  while   dataFile fail    amp  amp   dataFile eof            dataFile  gt  gt  name        test push back name     dataFile close

User · Answer

1  In the loop you are assigning value rather than comparing value so   i   Main size   -1  -  i  -1  since Main size    Main i  will yield  Vector Subscript out of Range  coz i   -1   2  You get Main size   as 0 maybe becuase its not it can t find the file  Give the file path and check the output  Also it would  be good to initialize the variables

User · Answer

file name must be of the form filename yourfileExtension        std  vector lt std  string gt  source  bool getFileContent std  string  amp  fileName        if  fileName substr fileName find last of        1     yourfileExtension                     Open the File         std  ifstream in fileName c str                 Check if object is valid         if   in                        std  cerr  lt  lt   Cannot open the File      lt  lt  fileName  lt  lt  std  endl              return false                    std  string str             Read the next line from File untill it reaches the end          while  std  getline in  str                            Line contains string of length  gt  0 then save it in vector             if  str size    gt  0                  source push back str                       for  size t i   0  i  lt  source size    i                  lexer source i   i           cout  lt  lt  source i   lt  lt  endl                         Close The File         in close            return true            else               std  cerr  lt  lt    VIP doe  s not support this file type   lt  lt  std  endl          std  cerr  lt  lt   supported extensions is filename yourfileExtension   lt  lt  endl

User · Answer

Your loop is wrong   for  int i 0  i   Main size   -1   i        Try this   for  int i 0  i  lt  Main size    i        Also  a more idiomatic way of reading numbers into a vector and writing them to stdout is something along these lines    include  lt iostream gt   include  lt iterator gt   include  lt fstream gt   include  lt vector gt   include  lt algorithm gt     for std  copy  int main       std  ifstream is  numbers txt      std  istream iterator lt double gt  start is   end    std  vector lt double gt  numbers start  end     std  cout  lt  lt   Read    lt  lt  numbers size    lt  lt    numbers   lt  lt  std  endl        print the numbers to stdout   std  cout  lt  lt   numbers read in  n     std  copy numbers begin    numbers end                 std  ostream iterator lt double gt  std  cout           std  cout  lt  lt  std  endl       although you should check the status of the ifstream for read errors

User · Answer

Just to expand on juanchopanza s answer a bit     for  int i 0  i   Main size   -1   i          cout  lt  lt  Main i   lt  lt    n       does this    Create i and set it to 0  Set i to Main size   - 1  Since Main is empty  Main size   is 0  and i gets set to -1  Main -1  is an out-of-bounds access  Kaboom

[c++] How to read a file into vector in C++?

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