How to read from stdin with fgets

Question

I ve written the following code to read a line from a terminal window  the problem is the code gets stuck in an infinite loop  The line sentence  is of undefined length  therefore I plan to read it in parts into the buffer  then concatenate it to another string which can be extended via realloc accordingly  Please can somebody spot my mistake or suggest a better way of achieving this    include  lt stdio h gt   include  lt string h gt    define BUFFERSIZE 10  int main  int argc  char  argv          char buffer BUFFERSIZE       printf  Enter a message   n        while fgets buffer  BUFFERSIZE   stdin     NULL                printf   s n   buffer             return 0

User · Answer

You have a wrong idea of what fgets returns. Take a look at this: http://www.cplusplus.com/reference/clibrary/cstdio/fgets/

It returns null when it finds an EOF character. Try running the program above and pressing CTRL+D (or whatever combination is your EOF character), and the loop will exit succesfully.

How do you want to detect the end of the input? Newline? Dot (you said sentence xD)?

User · Answer

here a concatenation solution    include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   define BUFFERSIZE 10  int main       char  text   calloc 1 1   buffer BUFFERSIZE     printf  Enter a message   n      while  fgets buffer  BUFFERSIZE   stdin       break with  D or  Z            text   realloc  text  strlen text  1 strlen buffer         if   text          error handling        strcat  text  buffer       note a   n  is appended here everytime        printf   s n   buffer         printf   ntext  n s  text     return 0

User · Answer

Assuming that you only want to read a single line  then use LINE MAX  which is defined in  lt limits h gt     include  lt stdio h gt   include  lt limits h gt      char line LINE MAX       if  fgets line  LINE MAX  stdin     NULL

User · Answer

Exits the loop if the line is empty Improving code     include  lt stdio h gt   include  lt string h gt      The value BUFFERSIZE can be changed to customer s taste   Changes the    size of the base array  string buffer        define BUFFERSIZE 10  int main void        char buffer BUFFERSIZE       char cChar      printf  Enter a message   n        while   fgets buffer  BUFFERSIZE  stdin        n                    For concatenation            fgets reads and adds   n  in the string   replace   n  by   0  to             remove the line break           if buffer strlen buffer  - 1       n               buffer strlen buffer  - 1      0              printf   s   buffer              Corrects the error mentioned by Alain BECKER                    Checks if the string buffer is full to check and prevent the             next character read by fgets is   n            if strlen buffer      BUFFERSIZE - 1   amp  amp   buffer strlen buffer  - 1       n                             Prevents end of the line   n  to be read in the first                 character  Loop Exit  in the next loop  Reads                the next char in stdin buffer   if   n  is read and removed  if                different is returned to stdin              cChar   fgetc stdin               if cChar      n                   ungetc cChar  stdin                  To print correctly if   n  is removed              else                 printf   n                        return 0      Exit when Enter is pressed    include  lt stdio h gt   include  lt stdbool h gt   include  lt string h gt   include  lt assert h gt    define BUFFERSIZE 16  int main void        char buffer BUFFERSIZE       printf  Enter a message   n        while true                assert fgets buffer  BUFFERSIZE  stdin     NULL              Verifies that the previous character to the last character in the            buffer array is   n   The last character is   0   if the            character is   n  leaves loop          if buffer strlen buffer  - 1       n                            fgets reads and adds   n  in the string  replace   n  by   0  to                 remove the line break               buffer strlen buffer  - 1      0               printf   s   buffer               break                    printf   s   buffer                return 0      Concatenation and dinamic allocation linked list  to a single string      Autor   Tiago Portela    Email   sapitando gmail com    Sobre   Compilado com TDM-GCC 5 10 64-bit e LCC-Win32 64-bit     Obs   Apenas tentando aprender algoritimos  sozinho  por hobby       include  lt stdio h gt   include  lt stdlib h gt   include  lt stdbool h gt   include  lt string h gt   include  lt assert h gt    define BUFFERSIZE 8  typedef struct  Node       char  lpBuffer      struct  Node  LpProxNode    Node t   LpNode t   int main void        char acBuffer BUFFERSIZE     0       LpNode t lpNode    LpNode t malloc sizeof Node t        assert lpNode  NULL       LpNode t lpHeadNode   lpNode      char  lpBuffer    char  calloc 1 sizeof char        assert lpBuffer  NULL       char cChar        printf  Enter a message   n           Exit when Enter is pressed     while true                assert fgets acBuffer  BUFFERSIZE  stdin   NULL           lpNode- gt lpBuffer    char  malloc  strlen acBuffer    1    sizeof char            assert lpNode- gt lpBuffer  NULL           strcpy lpNode- gt lpBuffer  acBuffer           if lpNode- gt lpBuffer strlen acBuffer  - 1       n                         lpNode- gt lpBuffer strlen acBuffer  - 1      0               lpNode- gt LpProxNode   NULL              break                    lpNode- gt LpProxNode    LpNode t malloc sizeof Node t            lpNode   lpNode- gt LpProxNode          assert lpNode  NULL                   Exits the loop if the line is empty Improving code       while true                assert fgets acBuffer  BUFFERSIZE  stdin   NULL           lpNode- gt lpBuffer    char  malloc  strlen acBuffer    1    sizeof char            assert lpNode- gt lpBuffer  NULL           strcpy lpNode- gt lpBuffer  acBuffer           if acBuffer strlen acBuffer  - 1       n               lpNode- gt lpBuffer strlen acBuffer  - 1      0           if strlen acBuffer      BUFFERSIZE - 1   amp  amp   acBuffer strlen acBuffer  - 1       n                          cChar   fgetc stdin               if cChar      n                   ungetc cChar  stdin                     if acBuffer 0       n                         lpNode- gt LpProxNode   NULL              break                    lpNode- gt LpProxNode    LpNode t malloc sizeof Node t            lpNode   lpNode- gt LpProxNode          assert lpNode  NULL               printf   nPseudo String   n        lpNode   lpHeadNode      while lpNode    NULL                printf   s   lpNode- gt lpBuffer           lpNode   lpNode- gt LpProxNode              printf   n nMemory blocks  n        lpNode   lpHeadNode      while lpNode    NULL                printf  Block    7s   size    lu n   lpNode- gt lpBuffer   long unsigned  strlen lpNode- gt lpBuffer    1            lpNode   lpNode- gt LpProxNode              printf   nConcatenated string  n        lpNode   lpHeadNode      while lpNode    NULL                lpBuffer    char  realloc lpBuffer   strlen lpBuffer    strlen lpNode- gt lpBuffer     1           strcat lpBuffer  lpNode- gt lpBuffer           lpNode   lpNode- gt LpProxNode            printf   s   lpBuffer       printf   n n            Deallocate memory     lpNode   lpHeadNode      while lpNode    NULL                lpHeadNode   lpNode- gt LpProxNode          free lpNode- gt lpBuffer           free lpNode           lpNode   lpHeadNode            lpBuffer    char  realloc lpBuffer  0       lpBuffer   NULL      if  lpNode    NULL   amp  amp   lpBuffer    NULL                  printf  Deallocate memory    s    char  lpNode             printf   n n         return 0

User · Answer

If you want to concatenate the input  then replace printf   s n   buffer   with strcat big buffer  buffer    Also create and initialize the big buffer at the beginning  char  big buffer   new char BIG BUFFERSIZE   big buffer 0      0    You should also prevent a buffer overrun by verifying the current buffer length plus the new buffer length does not exceed the limit  if   strlen big buffer    strlen buffer    lt  BIG BUFFERSIZE   The modified program would look like this    include  lt stdio h gt   include  lt string h gt    define BUFFERSIZE 10  define BIG BUFFERSIZE 1024  int main  int argc  char  argv          char buffer BUFFERSIZE       char  big buffer   new char BIG BUFFERSIZE       big buffer 0      0       printf  Enter a message   n        while fgets buffer  BUFFERSIZE   stdin     NULL                if   strlen big buffer    strlen buffer    lt  BIG BUFFERSIZE                        strcat big buffer  buffer                       return 0

[c] How to read from stdin with fgets()?

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