How to read a line from a text file in c c

Question

After exhaustive googling and visiting many forums  I am yet to find a good comprehensive answer for this question  A lot of the forums suggest using the get line  istream amp  getline  char  s  streamsize n   function  My question is what if I don t know what the length of each line is and cannot predict what the size may be  Also what is it s equivalent in C   Is there any specific function in c  c   to read one single line each time from a text file     Explanation   with Code snippets will help me a lot

User · Answer

im not really that good at C   but i believe this code should get you complete single line till the end       include lt stdio h gt    int main                char line 1024         FILE  f fopen  filename txt   r          fscanf  f      n   line         printf   s  line

User · Answer

In C    you can use the global function std  getline  it takes a string and a stream and an optional delimiter and reads 1 line until the delimiter specified is reached  An example    include  lt string gt   include  lt iostream gt   include  lt fstream gt   int main         std  ifstream input  filename txt        std  string line       while  std  getline  input  line               std  cout lt  lt line lt  lt   n              return 0      This program reads each line from a file and echos it to the console   For C you re probably looking at using fgets  it has been a while since I used C  meaning I m a bit rusty  but I believe you can use this to emulate the functionality of the above C   program like so    include  lt stdio h gt   int main         char line 1024       FILE  fp   fopen  filename txt   r           Checks if file is empty     if  fp    NULL                                    return 1             while  fgets line 1024 fp              printf   s n  line              return 0      With the limitation that the line can not be longer than the maximum length of the buffer that you re reading in to

User · Answer

In c  you could use fopen  and getch  Usually  if you can t be exactly sure of the length of the longest line  you could allocate a large buffer  e g  8kb  and almost be guaranteed of getting all lines   If there s a chance you may have really really long lines and you have to process line by line  you could malloc a resonable buffer  and use realloc to double it s size each time you get close to filling it    include  lt stdio h gt   include  lt stdlib h gt   void handle line char  line      printf   s   line      int main int argc  char  argv          int size   1024  pos      int c      char  buffer    char   malloc size        FILE  f   fopen  myfile txt    r        if f          do      read all lines in file         pos   0          do     read one line           c   fgetc f             if c    EOF  buffer pos       char c            if pos  gt   size - 1       increase buffer length - leave room for 0             size   2              buffer    char  realloc buffer  size                        while c    EOF  amp  amp  c      n            buffer pos    0             line is now in buffer         handle line buffer           while c    EOF          fclose f                        free buffer       return 0

User · Answer

In C  fgets    and you need to know the maximum size to prevent truncation

User · Answer

getline   is what you re looking for  You use strings in C    and you don t need to know the size ahead of time   Assuming std namespace    ifstream file1  myfile txt     string stuff    while  getline file1  stuff    n            cout  lt  lt  stuff  lt  lt  endl       file1 close

[c++] How to read a line from a text file in c/c++?

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