How best to read a File into List string

Question

I am using a list to limit the file size since the target is limited in disk and ram  This is what I am doing now but is there a more efficient way   readonly List lt string gt  LogList   new List lt string gt         var logFile   File ReadAllLines LOG PATH   foreach  var s in logFile  LogList Add s

User · Answer

You can simple read this way     List lt string gt  lines   System IO File ReadLines completePath  ToList

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A little update to Evan Mulawski answer to make it shorter  List lt string gt  allLinesText   File ReadAllLines fileName  ToList

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string inLine   reader ReadToEnd    myList   inLine Split new string       r n     StringSplitOptions None  ToList      I also use the Environment NewLine toCharArray as well  but found that didn t work on a couple files that did end in  r n   Try either one and I hope it works well for you

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string inLine   reader ReadToEnd    myList   inLine Split new string       r n     StringSplitOptions None  ToList      This answer misses the original point  which was that they were getting an OutOfMemory error    If you proceed with the above version  you are sure to hit it if your system does not have the appropriate CONTIGUOUS available ram to load the file   You simply must break it into parts  and either store as List or String   either way

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var logFile   File ReadAllLines LOG PATH   var logList   new List lt string gt  logFile     Since logFile is an array  you can pass it to the List lt T gt  constructor  This eliminates unnecessary overhead when iterating over the array  or using other IO classes   Actual constructor implementation   public List IEnumerable lt T gt  collection                        ICollection lt T gt  c   collection as ICollection lt T gt           if  c    null                int count   c Count              if  count    0                                 items    emptyArray                            else                    items   new T count                   c CopyTo  items  0                    size   count

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Edit   If you are doing this to trim the beginning of a log file  you can avoid loading the entire file by doing something like this      count the number of lines in the file int count   0  using  var sr   new StreamReader  file txt          while  sr ReadLine      null           count          skip first  LOG MAX - count  lines count   LOG MAX - count  using  var sr   new StreamReader  file txt    using  var sw   new StreamWriter  output txt             skip several lines     while  count  gt  0  amp  amp  sr ReadLine      null           count--          continue copying     string line           while   line   sr ReadLine       null          sw WriteLine line         First of all  since File ReadAllLines loads the entire file into a string array  string     copying to a list is redundant   Second  you must understand that a List is implemented using a dynamic array under the hood  This means that CLR will need to allocate and copy several arrays until it can accommodate the entire file  Since the file is already on disk  you might consider trading speed for memory and working on disk data directly  or processing it in smaller chunks    If you need to load it entirely in memory  at least try to leave in an array    string   lines   File ReadAllLines  file txt     If it really needs to be a List  load lines one by one    List lt string gt  lines   new List lt string gt      using  var sr   new StreamReader  file txt             while  sr Peek    gt   0            lines Add sr ReadLine          Note  List lt T gt  has a constructor which accepts a capacity parameter  If you know the number of lines in advance  you can prevent multiple allocations by preallocating the array in advance    List lt string gt  lines   new List lt string gt  NUMBER OF LINES    Even better  avoid storing the entire file in memory and process it  on the fly     using  var sr   new StreamReader  file txt             string line        while   line   sr ReadLine       null                        process the file line by line

User · Answer

Don t store it if possible   Just read through it if you are memory constrained   You can use a StreamReader   using  var reader   new StreamReader  file txt          var line   reader ReadLine           process line here     This can be wrapped in a method which yields strings per line read if you want to use LINQ

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this is only good in  NET 4   read your file  List lt string gt  ReadFile   File ReadAllLines   C  TEMP FILE TXT   ToList       manipulate data here foreach string line in ReadFile          do something here      write back to your file  File WriteAllLines   C  TEMP FILE2 TXT   ReadFile

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List lt string gt  lines   new List lt string gt      using  var sr   new StreamReader  file txt             while  sr Peek    gt   0            lines Add sr ReadLine          i would suggest this    of Groo s answer

User · Answer

Why not use a generator instead   private IEnumerable lt string gt  ReadLogLines string logPath        using StreamReader reader   File OpenText logPath             string line               while  line   reader ReadLine       null                yield return line                      Then you can use it like you would use the list   var logFile   ReadLogLines LOG PATH   foreach var s in logFile           Do whatever you need     Of course  if you need to have a List lt string gt   then you will need to keep the entire file contents in memory   There s really no way around that

[c#] How best to read a File into List<string>

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